{"id":790,"date":"2024-12-10T10:17:46","date_gmt":"2024-12-10T03:17:46","guid":{"rendered":"https:\/\/www.pgtutorial.com\/?page_id=790"},"modified":"2025-01-03T15:26:11","modified_gmt":"2025-01-03T08:26:11","slug":"postgresql-identity-column","status":"publish","type":"page","link":"https:\/\/www.pgtutorial.com\/postgresql-tutorial\/postgresql-identity-column\/","title":{"rendered":"PostgreSQL Identity Column"},"content":{"rendered":"\n<p><strong>Summary<\/strong>: in this tutorial, you&#8217;ll learn how to use the PostgreSQL identity column that automatically generates unique integers using an implicit sequence.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id='getting-started-with-the-postgresql-identity-column'>Getting Started with the PostgreSQL Identity Column <a href=\"#getting-started-with-the-postgresql-identity-column\" class=\"anchor\" id=\"getting-started-with-the-postgresql-identity-column\" title=\"Anchor for Getting Started with the PostgreSQL Identity Column\">#<\/a><\/h2>\n\n\n\n<p>In PostgreSQL, the identity column is a special feature that brings convenience by automatically generating unique integers using an implicit <a href=\"https:\/\/www.pgtutorial.com\/postgresql-tutorial\/postgresql-sequence\/\">sequence<\/a>.<\/p>\n\n\n\n<p>To define an identity column, you use one of two the following constraints:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><code>GENERATED ALWAYS AS IDENTITY<\/code>: This ensures the column always uses generated integer numbers. If a column has this constraint, you cannot provide an explicit value in the insert or update statement, except if you use the <code>OVERRIDING SYSTEM VALUE<\/code> in the <code><a href=\"https:\/\/www.pgtutorial.com\/postgresql-tutorial\/postgresql-insert\/\">INSERT<\/a><\/code> statement.<\/li>\n\n\n\n<li><code>GENERATED BY DEFAULT AS IDENTITY<\/code>: This constraint, similar to the above, offers flexibility by allowing you to provide an explicit integer for insertion.<\/li>\n<\/ul>\n\n\n\n<p>It&#8217;s typical to use the identity column as the <a href=\"https:\/\/www.pgtutorial.com\/postgresql-tutorial\/postgresql-primary-key\/\">primary key column<\/a> of a table, as it automatically generates unique integers, simplifying the management of primary keys.<\/p>\n\n\n\n<p>The following statement shows how to define a column as an identity column as a primary key column:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-1\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"><span class=\"hljs-keyword\">CREATE<\/span> <span class=\"hljs-keyword\">TABLE<\/span> <span class=\"hljs-built_in\">table_name<\/span> (\n  id <span class=\"hljs-type\">INT<\/span> <span class=\"hljs-keyword\">GENERATED<\/span> <span class=\"hljs-keyword\">ALWAYS<\/span> <span class=\"hljs-keyword\">AS<\/span> <span class=\"hljs-keyword\">IDENTITY<\/span> <span class=\"hljs-keyword\">PRIMARY KEY<\/span>,\n  column1 data_type,\n  ...\n);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-1\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Besides the <code>INT<\/code> data type, you can use the <code>SMALLINT<\/code> and <code>BIGINT<\/code> data types.<\/p>\n\n\n\n<p>Since the <code>id<\/code> column uses the <code>GENERATED AS ALWAYS IDENTITY<\/code> constraint, you cannot provide an id when inserting a row into the table.<\/p>\n\n\n\n<p>The following statement will fail:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-2\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"><span class=\"hljs-keyword\">INSERT<\/span> <span class=\"hljs-keyword\">INTO<\/span>\n  <span class=\"hljs-built_in\">table_name<\/span> (id, column1)\n<span class=\"hljs-keyword\">VALUES<\/span>\n  (<span class=\"hljs-number\">1<\/span>, value1);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-2\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>But if you have a good reason to use an explicit id value, the <code>OVERRIDING SYSTEM VALUE<\/code> clause in the <code>INSERT<\/code> statement gives you the control:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-3\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"><span class=\"hljs-keyword\">INSERT<\/span> <span class=\"hljs-keyword\">INTO<\/span>\n  <span class=\"hljs-built_in\">table_name<\/span> (id, column1) \n<span class=\"hljs-keyword\">OVERRIDING<\/span> <span class=\"hljs-keyword\">SYSTEM<\/span> <span class=\"hljs-keyword\">VALUE<\/span>\n<span class=\"hljs-keyword\">VALUES<\/span>\n  (<span class=\"hljs-number\">1<\/span>, value1);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-3\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>In this syntax, the <code>OVERRIDING SYSTEM VALUE<\/code> clause allows you to insert value one into the id column explicitly.<\/p>\n\n\n\n<p>The following shows how to define an identity column that uses the <code>GENERATED BY DEFAULT AS IDENTITY<\/code> constraint:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-4\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"><span class=\"hljs-keyword\">CREATE<\/span> <span class=\"hljs-keyword\">TABLE<\/span> <span class=\"hljs-built_in\">table_name<\/span> (\n\u00a0 \u00a0\u00a0id <span class=\"hljs-type\">INT<\/span> <span class=\"hljs-keyword\">GENERATED<\/span> <span class=\"hljs-keyword\">BY<\/span> <span class=\"hljs-keyword\">DEFAULT<\/span> <span class=\"hljs-keyword\">AS<\/span> <span class=\"hljs-keyword\">IDENTITY<\/span> <span class=\"hljs-keyword\">PRIMARY KEY<\/span>,\n\u00a0 \u00a0\u00a0column1 data_type,\n\u00a0 \u00a0\u00a0...\n);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-4\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>In this table, you can let the sequence generate unique integers or explicitly provide an integer in the <code>INSERT<\/code> statement:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-5\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"><span class=\"hljs-keyword\">INSERT<\/span> <span class=\"hljs-keyword\">INTO<\/span> <span class=\"hljs-built_in\">table_name<\/span>(id, column1)\n<span class=\"hljs-keyword\">VALUES<\/span>(<span class=\"hljs-number\">1<\/span>, value1);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-5\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<h2 class=\"wp-block-heading\" id='using-the-postgresql-identity-column-as-the-primary-key-column'>Using the PostgreSQL identity column as the primary key column <a href=\"#using-the-postgresql-identity-column-as-the-primary-key-column\" class=\"anchor\" id=\"using-the-postgresql-identity-column-as-the-primary-key-column\" title=\"Anchor for Using the PostgreSQL identity column as the primary key column\">#<\/a><\/h2>\n\n\n\n<p>First, create a table <code>sales_orders<\/code> that stores sales order headers:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-6\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"><span class=\"hljs-keyword\">CREATE<\/span> <span class=\"hljs-keyword\">TABLE<\/span> sales_orders(\n    order_no <span class=\"hljs-type\">INT<\/span> <span class=\"hljs-keyword\">GENERATED<\/span> <span class=\"hljs-keyword\">ALWAYS<\/span> <span class=\"hljs-keyword\">AS<\/span> <span class=\"hljs-keyword\">IDENTITY<\/span> <span class=\"hljs-keyword\">PRIMARY KEY<\/span>,\n    customer_name <span class=\"hljs-type\">VARCHAR<\/span>(<span class=\"hljs-number\">255<\/span>) <span class=\"hljs-keyword\">NOT<\/span> <span class=\"hljs-keyword\">NULL<\/span>,\n    status <span class=\"hljs-type\">VARCHAR<\/span>(<span class=\"hljs-number\">25<\/span>) <span class=\"hljs-keyword\">NOT<\/span> <span class=\"hljs-keyword\">NULL<\/span>,\n    requested_date <span class=\"hljs-type\">DATE<\/span> <span class=\"hljs-keyword\">NOT<\/span> <span class=\"hljs-keyword\">NULL<\/span>,\n    created_date <span class=\"hljs-type\">TIMESTAMPTZ<\/span> <span class=\"hljs-keyword\">NOT<\/span> <span class=\"hljs-keyword\">NULL<\/span> <span class=\"hljs-keyword\">DEFAULT<\/span> <span class=\"hljs-built_in\">CURRENT_TIMESTAMP<\/span>\n);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-6\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>The <code>id<\/code> column of the <code>sales_orders<\/code> table is an identity column.<\/p>\n\n\n\n<p>Second, insert two rows into the <code>sales_orders<\/code> table:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-7\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"><span class=\"hljs-keyword\">INSERT<\/span> <span class=\"hljs-keyword\">INTO<\/span>\n  sales_orders (customer_name, status, requested_date)\n<span class=\"hljs-keyword\">VALUES<\/span>\n  (<span class=\"hljs-string\">'John Doe'<\/span>, <span class=\"hljs-string\">'Pending'<\/span>, <span class=\"hljs-string\">'2024-12-15'<\/span>),\n  (<span class=\"hljs-string\">'Jane Doe'<\/span>, <span class=\"hljs-string\">'Completed'<\/span>, <span class=\"hljs-string\">'2024-12-20'<\/span>) \n<span class=\"hljs-keyword\">RETURNING<\/span> order_no;<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-7\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><a href=\"https:\/\/www.pgtutorial.com\/playground\/?db=id&amp;q=SU5TRVJUIElOVE8gc2FsZXNfb3JkZXJzIChjdXN0b21lcl9uYW1lLCBzdGF0dXMsIHJlcXVlc3RlZF9kYXRlKSBWQUxVRVMgKCdKb2huIERvZScsICdQZW5kaW5nJywgJzIwMjQtMTItMTUnKSwgKCdKYW5lIERvZScsICdDb21wbGV0ZWQnLCAnMjAyNC0xMi0yMCcpIFJFVFVSTklORyAqOw%3D%3D\" target=\"_blank\" rel=\"noreferrer noopener\">Try it<\/a><\/p>\n\n\n\n<p>Output:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-8\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"> order_no\n<span class=\"hljs-comment\">----------<\/span>\n        <span class=\"hljs-number\">1<\/span>\n        <span class=\"hljs-number\">2<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-8\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Since the <code>order_no<\/code> is an identity column, PostgreSQL automatically generates unique integers.<\/p>\n\n\n\n<p>The <code>id<\/code> column of the <code>sales_orders<\/code> table uses the <code>GENERATED ALWAYS AS IDENTITY<\/code> constraint. Therefore, it will not accept an implicit value.<\/p>\n\n\n\n<p>Third, attempt to insert a new row into the table with an implicit id:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-9\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"><span class=\"hljs-keyword\">INSERT<\/span> <span class=\"hljs-keyword\">INTO<\/span> sales_orders (order_no , customer_name, status, requested_date)\n<span class=\"hljs-keyword\">VALUES<\/span>(<span class=\"hljs-number\">3<\/span>, <span class=\"hljs-string\">'Adam Smith'<\/span>, <span class=\"hljs-string\">'Pending'<\/span>, <span class=\"hljs-string\">'2024-12-17'<\/span>);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-9\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><a href=\"https:\/\/www.pgtutorial.com\/playground\/?db=id&amp;q=SU5TRVJUIElOVE8gc2FsZXNfb3JkZXJzIChvcmRlcl9ubyAsIGN1c3RvbWVyX25hbWUsIHN0YXR1cywgcmVxdWVzdGVkX2RhdGUpIFZBTFVFUygzLCAnQWRhbSBTbWl0aCcsICdQZW5kaW5nJywgJzIwMjQtMTItMTcnKTs%3D\" target=\"_blank\" rel=\"noreferrer noopener\">Try it<\/a><\/p>\n\n\n\n<p>Error:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-10\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"><span class=\"hljs-keyword\">Column<\/span> \"order_no\" <span class=\"hljs-keyword\">is<\/span> an <span class=\"hljs-keyword\">identity<\/span> <span class=\"hljs-keyword\">column<\/span> defined <span class=\"hljs-keyword\">as<\/span> <span class=\"hljs-keyword\">GENERATED<\/span> <span class=\"hljs-keyword\">ALWAYS<\/span>.<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-10\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>To insert a value into the <code>GENERATED ALWAYS AS IDENTITY<\/code> column, you can use the <code>OVERRIDING SYSTEM VALUE<\/code> clause in the insert statement:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-11\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"><span class=\"hljs-keyword\">INSERT<\/span> <span class=\"hljs-keyword\">INTO<\/span> sales_orders (order_no , customer_name, status, requested_date)\n<span class=\"hljs-keyword\">OVERRIDING<\/span> <span class=\"hljs-keyword\">SYSTEM<\/span> <span class=\"hljs-keyword\">VALUE<\/span>\n<span class=\"hljs-keyword\">VALUES<\/span>(<span class=\"hljs-number\">3<\/span>, <span class=\"hljs-string\">'Adam Smith'<\/span>, <span class=\"hljs-string\">'Pending'<\/span>, <span class=\"hljs-string\">'2024-12-17'<\/span>)\n<span class=\"hljs-keyword\">RETURNING<\/span> order_no;<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-11\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><a href=\"https:\/\/www.pgtutorial.com\/playground\/?db=id&amp;q=SU5TRVJUIElOVE8gc2FsZXNfb3JkZXJzIChvcmRlcl9ubyAsIGN1c3RvbWVyX25hbWUsIHN0YXR1cywgcmVxdWVzdGVkX2RhdGUpIE9WRVJSSURJTkcgU1lTVEVNIFZBTFVFIFZBTFVFUygzLCAnQWRhbSBTbWl0aCcsICdQZW5kaW5nJywgJzIwMjQtMTItMTcnKSBSRVRVUk5JTkcgKjs%3D\" target=\"_blank\" rel=\"noreferrer noopener\">Try it<\/a><\/p>\n\n\n\n<p>Output:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-12\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"> order_no\n<span class=\"hljs-comment\">----------<\/span>\n        <span class=\"hljs-number\">3<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-12\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<h2 class=\"wp-block-heading\" id='using-the-postgresql-identity-column-as-a-non-primary-key-column'>Using the PostgreSQL identity column as a non-primary key column <a href=\"#using-the-postgresql-identity-column-as-a-non-primary-key-column\" class=\"anchor\" id=\"using-the-postgresql-identity-column-as-a-non-primary-key-column\" title=\"Anchor for Using the PostgreSQL identity column as a non-primary key column\">#<\/a><\/h2>\n\n\n\n<p>First, create a new table called <code>sales_order_items<\/code> that stores the items of sales orders:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-13\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"><span class=\"hljs-keyword\">CREATE<\/span> <span class=\"hljs-keyword\">TABLE<\/span> sales_order_items (\n  order_no <span class=\"hljs-type\">INT<\/span>,\n  item_no <span class=\"hljs-type\">INT<\/span> <span class=\"hljs-keyword\">GENERATED<\/span> <span class=\"hljs-keyword\">BY<\/span> <span class=\"hljs-keyword\">DEFAULT<\/span> <span class=\"hljs-keyword\">AS<\/span> <span class=\"hljs-keyword\">IDENTITY<\/span> <span class=\"hljs-keyword\">UNIQUE<\/span>,\n  product_name <span class=\"hljs-type\">VARCHAR<\/span>(<span class=\"hljs-number\">255<\/span>) <span class=\"hljs-keyword\">NOT<\/span> <span class=\"hljs-keyword\">NULL<\/span>,\n  quantity <span class=\"hljs-type\">INT<\/span> <span class=\"hljs-keyword\">NOT<\/span> <span class=\"hljs-keyword\">NULL<\/span> <span class=\"hljs-keyword\">CHECK<\/span> (quantity &gt; <span class=\"hljs-number\">0<\/span>),\n  price <span class=\"hljs-type\">DEC<\/span>(<span class=\"hljs-number\">15<\/span>, <span class=\"hljs-number\">2<\/span>) <span class=\"hljs-keyword\">NOT<\/span> <span class=\"hljs-keyword\">NULL<\/span> <span class=\"hljs-keyword\">CHECK<\/span> (price &gt; <span class=\"hljs-number\">0<\/span>),\n  <span class=\"hljs-keyword\">PRIMARY KEY<\/span> (order_no, item_no),\n  <span class=\"hljs-keyword\">FOREIGN KEY<\/span> (order_no) <span class=\"hljs-keyword\">REFERENCES<\/span> sales_orders (order_no) <span class=\"hljs-keyword\">ON<\/span> <span class=\"hljs-keyword\">DELETE<\/span> <span class=\"hljs-keyword\">CASCADE<\/span>\n);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-13\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Second, add two items to the order #1:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-14\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"><span class=\"hljs-keyword\">INSERT<\/span> <span class=\"hljs-keyword\">INTO<\/span>\n  sales_order_items (order_no, product_name, quantity, price)\n<span class=\"hljs-keyword\">VALUES<\/span>\n  (<span class=\"hljs-number\">1<\/span>, <span class=\"hljs-string\">'iPhone 16 Pro'<\/span>, <span class=\"hljs-number\">5<\/span>, <span class=\"hljs-number\">1299.99<\/span>),\n  (<span class=\"hljs-number\">1<\/span>, <span class=\"hljs-string\">'Screen Protector'<\/span>, <span class=\"hljs-number\">5<\/span>, <span class=\"hljs-number\">9.99<\/span>) \n<span class=\"hljs-keyword\">RETURNING<\/span> order_no, item_no;<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-14\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><a href=\"https:\/\/www.pgtutorial.com\/playground\/?db=id&amp;q=SU5TRVJUIElOVE8gc2FsZXNfb3JkZXJfaXRlbXMgKG9yZGVyX25vLCBwcm9kdWN0X25hbWUsIHF1YW50aXR5LCBwcmljZSkgVkFMVUVTICgxLCAnaVBob25lIDE2IFBybycsIDUsIDEyOTkuOTkpLCAoMSwgJ1NjcmVlbiBQcm90ZWN0b3InLCA1LCA5Ljk5KSBSRVRVUk5JTkcgb3JkZXJfbm8sIGl0ZW1fbm87\" target=\"_blank\" rel=\"noreferrer noopener\">Try it<\/a><\/p>\n\n\n\n<p>Output:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-15\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"> order_no | item_no\n<span class=\"hljs-comment\">----------+---------<\/span>\n        <span class=\"hljs-number\">1<\/span> |       <span class=\"hljs-number\">1<\/span>\n        <span class=\"hljs-number\">1<\/span> |       <span class=\"hljs-number\">2<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-15\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Third, add a new item into to the sales order one but provide the <code>item_no<\/code> value explicitly:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-16\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"><span class=\"hljs-keyword\">INSERT<\/span> <span class=\"hljs-keyword\">INTO<\/span>\n  sales_order_items (order_no, item_no, product_name, quantity, price)\n<span class=\"hljs-keyword\">VALUES<\/span>\n  (<span class=\"hljs-number\">1<\/span>, <span class=\"hljs-number\">3<\/span>, <span class=\"hljs-string\">'Charger'<\/span>, <span class=\"hljs-number\">5<\/span>, <span class=\"hljs-number\">29.99<\/span>)\n<span class=\"hljs-keyword\">RETURNING<\/span> order_no, item_no;<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-16\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><a href=\"https:\/\/www.pgtutorial.com\/playground\/?db=id&amp;q=SU5TRVJUIElOVE8gc2FsZXNfb3JkZXJfaXRlbXMgKG9yZGVyX25vLCBpdGVtX25vLCBwcm9kdWN0X25hbWUsIHF1YW50aXR5LCBwcmljZSkgVkFMVUVTICgxLCAzLCAnQ2hhcmdlcicsIDUsIDI5Ljk5KSBSRVRVUk5JTkcgb3JkZXJfbm8sIGl0ZW1fbm87\" target=\"_blank\" rel=\"noreferrer noopener\">Try it<\/a><\/p>\n\n\n\n<p>Output:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-17\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"> order_no | item_no\n<span class=\"hljs-comment\">----------+---------<\/span>\n        <span class=\"hljs-number\">1<\/span> |       <span class=\"hljs-number\">3<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-17\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Since the <code>item_no<\/code> column uses the <code>GENERATED BY DEFAULT AS IDENTITY<\/code> constraint, we can explicitly insert an integer into it.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id='implicit-sequences'>Implicit Sequences <a href=\"#implicit-sequences\" class=\"anchor\" id=\"implicit-sequences\" title=\"Anchor for Implicit Sequences\">#<\/a><\/h2>\n\n\n\n<p>When you create an identity column for a table, PostgreSQL automatically generates an implicit sequence and associates it with the column.<\/p>\n\n\n\n<p>The sequence will have the following naming convention:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-18\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\">&lt;<span class=\"hljs-built_in\">table_name<\/span>&gt;_&lt;<span class=\"hljs-built_in\">column_name<\/span>&gt;_seq<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-18\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>For example, PostgreSQL creates the following sequence for the <code>order_no<\/code> column of the <code>sales_orders<\/code> table:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-19\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\">sales_orders_order_no_seq<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-19\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Similarly, it creates the following sequence for the <code>item_no<\/code> column of the <code>sales_order_items<\/code> table:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-20\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\">sales_order_items_item_no_seq<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-20\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>PostgreSQL allows you to configure the sequence when defining an identity column.<\/p>\n\n\n\n<p>For example, the following creates a table <code>sales_order_item_schedules<\/code> that stores the scheduling of delivery dates and quantities for each line item in a sales order.<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-21\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"><span class=\"hljs-keyword\">CREATE<\/span> <span class=\"hljs-keyword\">TABLE<\/span> sales_order_item_schedules (\n  item_no <span class=\"hljs-type\">INT<\/span>,\n  schedule_no <span class=\"hljs-type\">INT<\/span> <span class=\"hljs-keyword\">GENERATED<\/span> <span class=\"hljs-keyword\">BY<\/span> <span class=\"hljs-keyword\">DEFAULT<\/span> <span class=\"hljs-keyword\">AS<\/span> <span class=\"hljs-keyword\">IDENTITY<\/span> (<span class=\"hljs-keyword\">INCREMENT<\/span> <span class=\"hljs-number\">10<\/span> <span class=\"hljs-keyword\">START<\/span> <span class=\"hljs-number\">10<\/span>),\n  delivery_qty <span class=\"hljs-type\">INT<\/span> <span class=\"hljs-keyword\">NOT<\/span> <span class=\"hljs-keyword\">NULL<\/span>,\n  delivered_on <span class=\"hljs-type\">DATE<\/span> <span class=\"hljs-keyword\">NOT<\/span> <span class=\"hljs-keyword\">NULL<\/span>,\n  <span class=\"hljs-keyword\">PRIMARY KEY<\/span> (item_no, schedule_no),\n  <span class=\"hljs-keyword\">FOREIGN KEY<\/span> (item_no)  \n      <span class=\"hljs-keyword\">REFERENCES<\/span> sales_order_items (item_no) \n      <span class=\"hljs-keyword\">ON<\/span> <span class=\"hljs-keyword\">DELETE<\/span> <span class=\"hljs-keyword\">CASCADE<\/span>\n);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-21\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>The <code>schedule_no<\/code> column is an identity column. Additionally, we configure the underlying sequence so the number starts at ten and increments by ten for each sales order line item.<\/p>\n\n\n\n<p>The following statement inserts three rows into the <code>sales_order_item_schedules<\/code> table:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-22\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"><span class=\"hljs-keyword\">INSERT<\/span> <span class=\"hljs-keyword\">INTO<\/span>\n  sales_order_item_schedules (item_no, delivery_qty, delivered_on)\n<span class=\"hljs-keyword\">VALUES<\/span>\n  (<span class=\"hljs-number\">1<\/span>, <span class=\"hljs-number\">1<\/span>, <span class=\"hljs-string\">'2024-12-16'<\/span>),\n  (<span class=\"hljs-number\">1<\/span>, <span class=\"hljs-number\">2<\/span>, <span class=\"hljs-string\">'2024-12-17'<\/span>),\n  (<span class=\"hljs-number\">1<\/span>, <span class=\"hljs-number\">2<\/span>, <span class=\"hljs-string\">'2024-12-17'<\/span>) \n<span class=\"hljs-keyword\">RETURNING<\/span> item_no, schedule_no ;<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-22\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><a href=\"https:\/\/www.pgtutorial.com\/playground\/?db=id&amp;q=SU5TRVJUIElOVE8gc2FsZXNfb3JkZXJfaXRlbV9zY2hlZHVsZXMgKGl0ZW1fbm8sIGRlbGl2ZXJ5X3F0eSwgZGVsaXZlcmVkX29uKSBWQUxVRVMgKDEsIDEsICcyMDI0LTEyLTE2JyksICgxLCAyLCAnMjAyNC0xMi0xNycpLCAoMSwgMiwgJzIwMjQtMTItMTcnKSBSRVRVUk5JTkcgaXRlbV9ubywgc2NoZWR1bGVfbm8gOw%3D%3D\" target=\"_blank\" rel=\"noreferrer noopener\">Try it<\/a><\/p>\n\n\n\n<p>Output:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-23\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"> item_no | schedule_no\n<span class=\"hljs-comment\">---------+-------------<\/span>\n       <span class=\"hljs-number\">1<\/span> |          <span class=\"hljs-number\">10<\/span>\n       <span class=\"hljs-number\">1<\/span> |          <span class=\"hljs-number\">20<\/span>\n       <span class=\"hljs-number\">1<\/span> |          <span class=\"hljs-number\">30<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-23\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>The output indicates that the values in the <code>schedule_no<\/code> column start at ten and increment by for each row.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id='configuring-an-existing-column-as-an-identity-column'>Configuring an existing column as an identity column <a href=\"#configuring-an-existing-column-as-an-identity-column\" class=\"anchor\" id=\"configuring-an-existing-column-as-an-identity-column\" title=\"Anchor for Configuring an existing column as an identity column\">#<\/a><\/h2>\n\n\n\n<p>To change a column to an identity column, you can use the <code>ALTER TABLE<\/code> statement:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-24\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"><span class=\"hljs-keyword\">ALTER<\/span> <span class=\"hljs-keyword\">TABLE<\/span> <span class=\"hljs-built_in\">table_name<\/span>\n<span class=\"hljs-keyword\">ALTER<\/span> <span class=\"hljs-keyword\">COLUMN<\/span> <span class=\"hljs-built_in\">column_name<\/span>\n<span class=\"hljs-keyword\">ADD<\/span> <span class=\"hljs-keyword\">GENERATED<\/span> { <span class=\"hljs-keyword\">ALWAYS<\/span> | <span class=\"hljs-keyword\">BY<\/span> <span class=\"hljs-keyword\">DEFAULT<\/span> } \n<span class=\"hljs-keyword\">AS<\/span> <span class=\"hljs-keyword\">IDENTITY<\/span> \n&#91;sequence_option];<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-24\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>The <code>column_name<\/code> must have a <code><a href=\"https:\/\/www.pgtutorial.com\/postgresql-tutorial\/postgresql-not-null\/\">NOT NULL<\/a><\/code>constraint or you&#8217;ll encounter an error.<\/p>\n\n\n\n<p>Let&#8217;s take an example:<\/p>\n\n\n\n<p>First, create a table <code>taxes<\/code> to store sales taxes:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-25\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"><span class=\"hljs-keyword\">CREATE<\/span> <span class=\"hljs-keyword\">TABLE<\/span> taxes (\n   id <span class=\"hljs-type\">INT<\/span> <span class=\"hljs-keyword\">PRIMARY KEY<\/span>, \n   rate <span class=\"hljs-type\">DECIMAL<\/span>(<span class=\"hljs-number\">5<\/span>, <span class=\"hljs-number\">2<\/span>) <span class=\"hljs-keyword\">NOT<\/span> <span class=\"hljs-keyword\">NULL<\/span>\n);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-25\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><a href=\"https:\/\/www.pgtutorial.com\/playground\/?db=id&amp;q=Q1JFQVRFIFRBQkxFIHRheGVzICggaWQgSU5UIFBSSU1BUlkgS0VZLCByYXRlIERFQ0lNQUwoNSwgMikgTk9UIE5VTEwgKTs%3D\" target=\"_blank\" rel=\"noreferrer noopener\">Try it<\/a><\/p>\n\n\n\n<p>Second, set the <code>id<\/code> column as an identity column:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-26\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"><span class=\"hljs-keyword\">ALTER<\/span> <span class=\"hljs-keyword\">TABLE<\/span> taxes\n<span class=\"hljs-keyword\">ALTER<\/span> <span class=\"hljs-keyword\">COLUMN<\/span> id \n<span class=\"hljs-keyword\">ADD<\/span> <span class=\"hljs-keyword\">GENERATED<\/span> <span class=\"hljs-keyword\">ALWAYS<\/span> <span class=\"hljs-keyword\">AS<\/span> <span class=\"hljs-keyword\">IDENTITY<\/span>;<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-26\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><a href=\"https:\/\/www.pgtutorial.com\/playground\/?db=id&amp;q=QUxURVIgVEFCTEUgdGF4ZXMgQUxURVIgQ09MVU1OIGlkIEFERCBHRU5FUkFURUQgQUxXQVlTIEFTIElERU5USVRZOw%3D%3D\" target=\"_blank\" rel=\"noreferrer noopener\">Try it<\/a><\/p>\n\n\n\n<p>Third, insert some rows into the <code>taxes<\/code> table:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-27\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"><span class=\"hljs-keyword\">INSERT<\/span> <span class=\"hljs-keyword\">INTO<\/span>\n  taxes (rate)\n<span class=\"hljs-keyword\">values<\/span>\n  (<span class=\"hljs-number\">0.05<\/span>),\n  (<span class=\"hljs-number\">0.08<\/span>) \n<span class=\"hljs-keyword\">RETURNING<\/span> *;<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-27\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><a href=\"https:\/\/www.pgtutorial.com\/playground\/?db=id&amp;q=SU5TRVJUIElOVE8gdGF4ZXMgKHJhdGUpIHZhbHVlcyAoMC4wNSksICgwLjA4KSBSRVRVUk5JTkcgKjs%3D\" target=\"_blank\" rel=\"noreferrer noopener\">Try it<\/a><\/p>\n\n\n\n<p>Output:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-28\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"> id | rate\n<span class=\"hljs-comment\">----+------<\/span>\n  <span class=\"hljs-number\">1<\/span> | <span class=\"hljs-number\">0.05<\/span>\n  <span class=\"hljs-number\">2<\/span> | <span class=\"hljs-number\">0.08<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-28\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<h2 class=\"wp-block-heading\" id='setting-identity-column-characteristics'>Setting identity column characteristics <a href=\"#setting-identity-column-characteristics\" class=\"anchor\" id=\"setting-identity-column-characteristics\" title=\"Anchor for Setting identity column characteristics\">#<\/a><\/h2>\n\n\n\n<p>PostgreSQL allows you to configure the characteristics of an identity column:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Switching between the <code>GENERATED ALWAYS<\/code> and <code>GENERATED BY DEFAULT<\/code>.<\/li>\n\n\n\n<li>Change the parameters for the implicit sequence.<\/li>\n<\/ul>\n\n\n\n<p>Here&#8217;s the syntax:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-29\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"><span class=\"hljs-keyword\">ALTER<\/span> <span class=\"hljs-keyword\">TABLE<\/span> <span class=\"hljs-built_in\">table_name<\/span>\n<span class=\"hljs-keyword\">ALTER<\/span> <span class=\"hljs-keyword\">COLUMN<\/span> <span class=\"hljs-built_in\">column_name<\/span>\n<span class=\"hljs-keyword\">SET<\/span> <span class=\"hljs-keyword\">GENERATED<\/span> { <span class=\"hljs-keyword\">ALWAYS<\/span> | <span class=\"hljs-keyword\">BY<\/span> <span class=\"hljs-keyword\">DEFAULT<\/span>}\n&#91;<span class=\"hljs-keyword\">SET<\/span> sequence_option]<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-29\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>For example:<\/p>\n\n\n\n<p>First, change the id column of the taxes table from <code>GENERATED ALWAYS<\/code> to <code>GENERATED BY DEFAULT<\/code>:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-30\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"><span class=\"hljs-keyword\">ALTER<\/span> <span class=\"hljs-keyword\">TABLE<\/span> taxes\n<span class=\"hljs-keyword\">ALTER<\/span> <span class=\"hljs-keyword\">COLUMN<\/span> id\n<span class=\"hljs-keyword\">SET<\/span> <span class=\"hljs-keyword\">GENERATED<\/span> <span class=\"hljs-keyword\">BY<\/span> <span class=\"hljs-keyword\">DEFAULT<\/span>;<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-30\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><a href=\"https:\/\/www.pgtutorial.com\/playground\/?db=id&amp;q=QUxURVIgVEFCTEUgdGF4ZXMgQUxURVIgQ09MVU1OIGlkIFNFVCBHRU5FUkFURUQgQlkgREVGQVVMVDs%3D\" target=\"_blank\" rel=\"noreferrer noopener\">Try it<\/a><\/p>\n\n\n\n<p>Second, insert an explicit integer value into the id column of the taxes table:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-31\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"><span class=\"hljs-keyword\">INSERT<\/span> <span class=\"hljs-keyword\">INTO<\/span> taxes(id, rate)\n<span class=\"hljs-keyword\">VALUES<\/span>(<span class=\"hljs-number\">3<\/span>, <span class=\"hljs-number\">0.1<\/span>)\n<span class=\"hljs-keyword\">RETURNING<\/span> *;<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-31\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><a href=\"https:\/\/www.pgtutorial.com\/playground\/?db=id&amp;q=SU5TRVJUIElOVE8gdGF4ZXMoaWQsIHJhdGUpIFZBTFVFUygzLCAwLjEpIFJFVFVSTklORyAqOw%3D%3D\" target=\"_blank\" rel=\"noreferrer noopener\">Try it<\/a><\/p>\n\n\n\n<p>Output:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-32\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"> id | rate\n<span class=\"hljs-comment\">----+------<\/span>\n  <span class=\"hljs-number\">3<\/span> | <span class=\"hljs-number\">0.10<\/span><\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-32\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Third, set the increment value by 5, instead of using 1 by default:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-33\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"><span class=\"hljs-keyword\">ALTER<\/span> <span class=\"hljs-keyword\">TABLE<\/span> taxes\n<span class=\"hljs-keyword\">ALTER<\/span> <span class=\"hljs-keyword\">COLUMN<\/span> id\n<span class=\"hljs-keyword\">SET<\/span> <span class=\"hljs-keyword\">INCREMENT<\/span> <span class=\"hljs-keyword\">BY<\/span> <span class=\"hljs-number\">5<\/span>;<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-33\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Finally, insert a new row into the <code>taxes<\/code> table:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-34\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"><span class=\"hljs-keyword\">INSERT<\/span> <span class=\"hljs-keyword\">INTO<\/span> taxes(rate)\n<span class=\"hljs-keyword\">VALUES<\/span>(<span class=\"hljs-number\">0.12<\/span>)\n<span class=\"hljs-keyword\">RETURNING<\/span> *;<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-34\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>The id value is seven instead, not 8 (3 + 5), because the sequence did not generate the number 3. It returns the next sequence value, 7 ( 2 + 5 ).<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id='removing-generated-always-or-by-default-as-identity-constraints'>Removing GENERATED ALWAYS (or BY DEFAULT) AS IDENTITY constraints <a href=\"#removing-generated-always-or-by-default-as-identity-constraints\" class=\"anchor\" id=\"removing-generated-always-or-by-default-as-identity-constraints\" title=\"Anchor for Removing GENERATED ALWAYS (or BY DEFAULT) AS IDENTITY constraints\">#<\/a><\/h2>\n\n\n\n<p>To drop a <code>GENERATED ALWAYS<\/code> (or <code>BY DEFAULT<\/code>) <code>AS IDENTITY<\/code> constraint from a column, you use the <code>ALTER TABLE DROP IDENTITY<\/code> statement:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-35\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"><span class=\"hljs-keyword\">ALTER<\/span> <span class=\"hljs-keyword\">TABLE<\/span> <span class=\"hljs-built_in\">table_name<\/span>\n<span class=\"hljs-keyword\">ALTER<\/span> <span class=\"hljs-keyword\">COLUMN<\/span> <span class=\"hljs-built_in\">column_name<\/span>\n<span class=\"hljs-keyword\">DROP<\/span> <span class=\"hljs-keyword\">IDENTITY<\/span> &#91; <span class=\"hljs-keyword\">IF<\/span> <span class=\"hljs-keyword\">EXISTS<\/span> ];<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-35\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>The <code>IF EXISTS<\/code> clause conditionally drops the identity constraint only if it exists.<\/p>\n\n\n\n<p>For example, the following statement removes the <code>GENERATED ALWAYS<\/code> (or <code>BY DEFAULT<\/code>) <code>AS IDENTITY<\/code> constraint from the <code>id<\/code> column of the <code>taxes<\/code> table:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-36\" data-shcb-language-name=\"PostgreSQL SQL dialect and PL\/pgSQL\" data-shcb-language-slug=\"pgsql\"><span><code class=\"hljs language-pgsql\"><span class=\"hljs-keyword\">ALTER<\/span> <span class=\"hljs-keyword\">TABLE<\/span> taxes\n<span class=\"hljs-keyword\">ALTER<\/span> <span class=\"hljs-keyword\">COLUMN<\/span> id\n<span class=\"hljs-keyword\">DROP<\/span> <span class=\"hljs-keyword\">IDENTITY<\/span> <span class=\"hljs-keyword\">IF<\/span> <span class=\"hljs-keyword\">EXISTS<\/span>;<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-36\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PostgreSQL SQL dialect and PL\/pgSQL<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">pgsql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p><a href=\"https:\/\/www.pgtutorial.com\/playground\/?db=id&amp;q=QUxURVIgVEFCTEUgdGF4ZXMgQUxURVIgQ09MVU1OIGlkIERST1AgSURFTlRJVFkgSUYgRVhJU1RTOw%3D%3D\" target=\"_blank\" rel=\"noreferrer noopener\">Try it<\/a><\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id='summary'>Summary <a href=\"#summary\" class=\"anchor\" id=\"summary\" title=\"Anchor for Summary\">#<\/a><\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Use the identity column to generate unique integers using an implicit sequence.<\/li>\n\n\n\n<li>Set up an identity column using the <code>GENERATED AWAYS AS IDENTITY<\/code> or <code>GENERATED BY DEFAULT AS DEFAULT<\/code> constraint.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id='quiz'>Quiz <a href=\"#quiz\" class=\"anchor\" id=\"quiz\" title=\"Anchor for Quiz\">#<\/a><\/h2>\n\n\n\n<iframe loading=\"lazy\"\n  name=\"quiz\"\n  src=\"\/quiz\/?quiz=identity-column\"\n  height=\"700\"\n  width=\"600\"\n  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