{"id":1778,"date":"2019-04-21T09:06:32","date_gmt":"2019-04-21T02:06:32","guid":{"rendered":"http:\/\/www.sqlservertutorial.net\/?page_id=1778"},"modified":"2024-03-14T16:02:21","modified_gmt":"2024-03-14T09:02:21","slug":"sql-server-unique-index","status":"publish","type":"page","link":"https:\/\/www.sqlservertutorial.net\/sql-server-indexes\/sql-server-unique-index\/","title":{"rendered":"SQL Server Unique Index"},"content":{"rendered":"\n<p><strong>Summary<\/strong>: in this tutorial, you will learn about SQL Server unique indexes and how to use them to enforce the uniqueness of values in one or more columns of a table.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id='sql-server-unique-index-overview'>SQL Server unique index overview <a href=\"#sql-server-unique-index-overview\" class=\"anchor\" id=\"sql-server-unique-index-overview\" title=\"Anchor for SQL Server unique index overview\">#<\/a><\/h2>\n\n\n\n<p>A unique index ensures the index key columns do not contain any duplicate values.<\/p>\n\n\n\n<p>A unique index may consist of one or many columns. If a unique index has one column, the values in this column will be unique. In case the unique index has multiple columns, the combination of values in these columns is unique.<\/p>\n\n\n\n<p>Any attempt to <a href=\"https:\/\/www.sqlservertutorial.net\/sql-server-basics\/sql-server-insert\/\">insert<\/a> or <a href=\"https:\/\/www.sqlservertutorial.net\/sql-server-basics\/sql-server-update\/\">update<\/a> data into the unique index key columns that cause the duplicate will result in an error.<\/p>\n\n\n\n<p>A unique index can be <a href=\"https:\/\/www.sqlservertutorial.net\/sql-server-indexes\/sql-server-clustered-indexes\/\">clustered<\/a> or <a href=\"https:\/\/www.sqlservertutorial.net\/sql-server-indexes\/sql-server-create-index\/\">non-clustered<\/a>.<\/p>\n\n\n\n<p>To create a unique index, you use the <code>CREATE UNIQUE INDEX<\/code> statement as follows:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-1\" data-shcb-language-name=\"SQL (Structured Query Language)\" data-shcb-language-slug=\"sql\"><span><code class=\"hljs language-sql\"><span class=\"hljs-keyword\">CREATE<\/span> <span class=\"hljs-keyword\">UNIQUE<\/span> <span class=\"hljs-keyword\">INDEX<\/span> index_name\n<span class=\"hljs-keyword\">ON<\/span> table_name(column_list);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-1\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">SQL (Structured Query Language)<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">sql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>In this syntax:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>First, specify the name of the unique index after the <code>CREATE UNIQUE INDEX<\/code> keywords.<\/li>\n\n\n\n<li>Second, specify the name of the table to which the index is associated and a list of columns that will be included in the index.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id='sql-server-unique-index-examples'>SQL Server unique index examples <a href=\"#sql-server-unique-index-examples\" class=\"anchor\" id=\"sql-server-unique-index-examples\" title=\"Anchor for SQL Server unique index examples\">#<\/a><\/h2>\n\n\n\n<p>Let&#8217;s take some examples of using unique indexes.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id='1-creating-a-sql-server-unique-index-for-one-column-example'>1) Creating a SQL Server unique index for one column example <a href=\"#1-creating-a-sql-server-unique-index-for-one-column-example\" class=\"anchor\" id=\"1-creating-a-sql-server-unique-index-for-one-column-example\" title=\"Anchor for 1) Creating a SQL Server unique index for one column example\">#<\/a><\/h3>\n\n\n\n<p>This query finds the customer with the email <code>'caren.stephens@msn.com'<\/code>:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-2\" data-shcb-language-name=\"SQL (Structured Query Language)\" data-shcb-language-slug=\"sql\"><span><code class=\"hljs language-sql\"><span class=\"hljs-keyword\">SELECT<\/span>\n    customer_id, \n    email \n<span class=\"hljs-keyword\">FROM<\/span>\n    sales.customers\n<span class=\"hljs-keyword\">WHERE<\/span> \n    email = <span class=\"hljs-string\">'caren.stephens@msn.com'<\/span>;\n<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-2\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">SQL (Structured Query Language)<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">sql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<figure class=\"wp-block-image\"><img loading=\"lazy\" decoding=\"async\" width=\"378\" height=\"84\" src=\"https:\/\/www.sqlservertutorial.net\/wp-content\/uploads\/SQL-Server-UNIQUE-Index-Clustered-Index-Scan.png\" alt=\"SQL Server UNIQUE Index - Clustered Index Scan\" class=\"wp-image-1779\" srcset=\"https:\/\/www.sqlservertutorial.net\/wp-content\/uploads\/SQL-Server-UNIQUE-Index-Clustered-Index-Scan.png 378w, https:\/\/www.sqlservertutorial.net\/wp-content\/uploads\/SQL-Server-UNIQUE-Index-Clustered-Index-Scan-300x67.png 300w\" sizes=\"auto, (max-width: 378px) 100vw, 378px\" \/><\/figure>\n\n\n\n<p>The query optimizer has to scan the whole clustered index to find the row.<\/p>\n\n\n\n<p>To speed up the retrieval of the query, you can add a non-clustered index to the <code>email<\/code> column.<\/p>\n\n\n\n<p>However, with the assumption that each customer will have a unique email, you can create a unique index for the <code>email<\/code> column.<\/p>\n\n\n\n<p>Because the <code>sales.customers<\/code> table already has data, you need to check duplicate values in the <code>email<\/code> column first:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-3\" data-shcb-language-name=\"SQL (Structured Query Language)\" data-shcb-language-slug=\"sql\"><span><code class=\"hljs language-sql\"><span class=\"hljs-keyword\">SELECT<\/span> \n    email, \n    <span class=\"hljs-keyword\">COUNT<\/span>(email)\n<span class=\"hljs-keyword\">FROM<\/span> \n    sales.customers\n<span class=\"hljs-keyword\">GROUP<\/span> <span class=\"hljs-keyword\">BY<\/span> \n    email\n<span class=\"hljs-keyword\">HAVING<\/span> \n    <span class=\"hljs-keyword\">COUNT<\/span>(email) &gt; <span class=\"hljs-number\">1<\/span>;\n<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-3\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">SQL (Structured Query Language)<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">sql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>The query returns an empty result set. It means that there are no duplicate values in the <code>email<\/code> column.<\/p>\n\n\n\n<p>Therefore, you can go ahead to create a unique index for the <code>email<\/code> column of the <code>sales.customers<\/code> table:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-4\" data-shcb-language-name=\"SQL (Structured Query Language)\" data-shcb-language-slug=\"sql\"><span><code class=\"hljs language-sql\"><span class=\"hljs-keyword\">CREATE<\/span> <span class=\"hljs-keyword\">UNIQUE<\/span> <span class=\"hljs-keyword\">INDEX<\/span> ix_cust_email \n<span class=\"hljs-keyword\">ON<\/span> sales.customers(email);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-4\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">SQL (Structured Query Language)<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">sql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>From now on, the query optimizer will leverage the <code>ix_cust_email<\/code> index and use the <code>index seek<\/code> method to search for rows by email.<\/p>\n\n\n\n<figure class=\"wp-block-image\"><img loading=\"lazy\" decoding=\"async\" width=\"317\" height=\"77\" src=\"https:\/\/www.sqlservertutorial.net\/wp-content\/uploads\/SQL-Server-UNIQUE-Index-Index-Seek.png\" alt=\"SQL Server UNIQUE Index - Index Seek\" class=\"wp-image-1780\" srcset=\"https:\/\/www.sqlservertutorial.net\/wp-content\/uploads\/SQL-Server-UNIQUE-Index-Index-Seek.png 317w, https:\/\/www.sqlservertutorial.net\/wp-content\/uploads\/SQL-Server-UNIQUE-Index-Index-Seek-300x73.png 300w\" sizes=\"auto, (max-width: 317px) 100vw, 317px\" \/><\/figure>\n\n\n\n<h3 class=\"wp-block-heading\" id='2-creating-a-sql-server-unique-index-for-multiple-columns'>2) Creating a SQL Server unique index for multiple columns <a href=\"#2-creating-a-sql-server-unique-index-for-multiple-columns\" class=\"anchor\" id=\"2-creating-a-sql-server-unique-index-for-multiple-columns\" title=\"Anchor for 2) Creating a SQL Server unique index for multiple columns\">#<\/a><\/h3>\n\n\n\n<p>First, <a href=\"https:\/\/www.sqlservertutorial.net\/sql-server-basics\/sql-server-create-table\/\">create a table<\/a> named <code>t1<\/code> that has two columns for the demonstration:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-5\" data-shcb-language-name=\"SQL (Structured Query Language)\" data-shcb-language-slug=\"sql\"><span><code class=\"hljs language-sql\"><span class=\"hljs-keyword\">CREATE<\/span> <span class=\"hljs-keyword\">TABLE<\/span> t1 (\n    a <span class=\"hljs-built_in\">INT<\/span>, \n    b <span class=\"hljs-built_in\">INT<\/span>\n);\n<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-5\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">SQL (Structured Query Language)<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">sql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Next, create a unique index that includes both <code>a<\/code> and <code>b<\/code> columns:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-6\" data-shcb-language-name=\"SQL (Structured Query Language)\" data-shcb-language-slug=\"sql\"><span><code class=\"hljs language-sql\"><span class=\"hljs-keyword\">CREATE<\/span> <span class=\"hljs-keyword\">UNIQUE<\/span> <span class=\"hljs-keyword\">INDEX<\/span> ix_uniq_ab \n<span class=\"hljs-keyword\">ON<\/span> t1(a, b);\n<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-6\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">SQL (Structured Query Language)<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">sql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Then, <a href=\"https:\/\/www.sqlservertutorial.net\/sql-server-basics\/sql-server-insert\/\">insert a new row<\/a> into the <code>t1<\/code> table:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-7\" data-shcb-language-name=\"SQL (Structured Query Language)\" data-shcb-language-slug=\"sql\"><span><code class=\"hljs language-sql\"><span class=\"hljs-keyword\">INSERT<\/span> <span class=\"hljs-keyword\">INTO<\/span> t1(a,b) <span class=\"hljs-keyword\">VALUES<\/span>(<span class=\"hljs-number\">1<\/span>,<span class=\"hljs-number\">1<\/span>);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-7\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">SQL (Structured Query Language)<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">sql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>After that, insert another row into the <code>t1<\/code> table. Note that the value 1 is repeated in the <code>a<\/code> column, but the combination of values in the column <code>a<\/code> and <code>b<\/code> is not duplicate:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-8\" data-shcb-language-name=\"SQL (Structured Query Language)\" data-shcb-language-slug=\"sql\"><span><code class=\"hljs language-sql\"><span class=\"hljs-keyword\">INSERT<\/span> <span class=\"hljs-keyword\">INTO<\/span> t1(a,b) <span class=\"hljs-keyword\">VALUES<\/span>(<span class=\"hljs-number\">1<\/span>,<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\">SQL (Structured Query Language)<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">sql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Finally, insert a row that already exists into the <code>t1<\/code> table:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-9\" data-shcb-language-name=\"SQL (Structured Query Language)\" data-shcb-language-slug=\"sql\"><span><code class=\"hljs language-sql\"><span class=\"hljs-keyword\">INSERT<\/span> <span class=\"hljs-keyword\">INTO<\/span> t1(a,b) <span class=\"hljs-keyword\">VALUES<\/span>(<span class=\"hljs-number\">1<\/span>,<span class=\"hljs-number\">2<\/span>);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-9\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">SQL (Structured Query Language)<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">sql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>SQL Server issues an error::<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-10\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript\">Cannot insert duplicate key row <span class=\"hljs-keyword\">in<\/span> object <span class=\"hljs-string\">'dbo.t1'<\/span> <span class=\"hljs-keyword\">with<\/span> unique index <span class=\"hljs-string\">'ix_ab'<\/span>. The duplicate key value is (<span class=\"hljs-number\">1<\/span>, <span class=\"hljs-number\">2<\/span>).<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-10\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<h2 class=\"wp-block-heading\" id='sql-server-unique-index-and-null'>SQL Server unique index and NULL <a href=\"#sql-server-unique-index-and-null\" class=\"anchor\" id=\"sql-server-unique-index-and-null\" title=\"Anchor for SQL Server unique index and NULL\">#<\/a><\/h2>\n\n\n\n<p><a href=\"https:\/\/www.sqlservertutorial.net\/sql-server-basics\/sql-server-null\/\">NULL<\/a> is special. It is a marker that indicates the missing information or not applicable.<\/p>\n\n\n\n<p>NULL is not even equal to itself. However, when it comes to a unique index, SQL Server treats NULL values the same. It means that if you create a unique index on a nullable column, you can have only one NULL value in this column<\/p>\n\n\n\n<p>The following statements <a href=\"https:\/\/www.sqlservertutorial.net\/sql-server-basics\/sql-server-create-table\/\">create a new table<\/a> named <code>t2<\/code> and define a unique index on the <code>a<\/code> column:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-11\" data-shcb-language-name=\"SQL (Structured Query Language)\" data-shcb-language-slug=\"sql\"><span><code class=\"hljs language-sql\"><span class=\"hljs-keyword\">CREATE<\/span> <span class=\"hljs-keyword\">TABLE<\/span> t2(\n    a <span class=\"hljs-built_in\">INT<\/span>\n);\n\n<span class=\"hljs-keyword\">CREATE<\/span> <span class=\"hljs-keyword\">UNIQUE<\/span> <span class=\"hljs-keyword\">INDEX<\/span> a_uniq_t2\n<span class=\"hljs-keyword\">ON<\/span> t2(a);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-11\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">SQL (Structured Query Language)<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">sql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>This query inserts NULL into the <code>a<\/code> column of the <code>t2<\/code> table:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-12\" data-shcb-language-name=\"SQL (Structured Query Language)\" data-shcb-language-slug=\"sql\"><span><code class=\"hljs language-sql\"><span class=\"hljs-keyword\">INSERT<\/span> <span class=\"hljs-keyword\">INTO<\/span> t2(a) <span class=\"hljs-keyword\">VALUES<\/span>(<span class=\"hljs-literal\">NULL<\/span>);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-12\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">SQL (Structured Query Language)<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">sql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>However, when executing the above query again, the SQL Server issues an error due to duplicate NULL values:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-13\" data-shcb-language-name=\"SQL (Structured Query Language)\" data-shcb-language-slug=\"sql\"><span><code class=\"hljs language-sql\">]Cannot <span class=\"hljs-keyword\">insert<\/span> <span class=\"hljs-keyword\">duplicate<\/span> <span class=\"hljs-keyword\">key<\/span> <span class=\"hljs-keyword\">row<\/span> <span class=\"hljs-keyword\">in<\/span> <span class=\"hljs-keyword\">object<\/span> <span class=\"hljs-string\">'dbo.t2'<\/span> <span class=\"hljs-keyword\">with<\/span> <span class=\"hljs-keyword\">unique<\/span> <span class=\"hljs-keyword\">index<\/span> <span class=\"hljs-string\">'a_uniq_t2'<\/span>. The <span class=\"hljs-keyword\">duplicate<\/span> <span class=\"hljs-keyword\">key<\/span> <span class=\"hljs-keyword\">value<\/span> <span class=\"hljs-keyword\">is<\/span> (&lt;<span class=\"hljs-literal\">NULL<\/span>&gt;). (<span class=\"hljs-number\">2601<\/span>)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-13\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">SQL (Structured Query Language)<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">sql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<h2 class=\"wp-block-heading\" id='unique-index-vs-unique-constraint'>Unique index vs. UNIQUE constraint <a href=\"#unique-index-vs-unique-constraint\" class=\"anchor\" id=\"unique-index-vs-unique-constraint\" title=\"Anchor for Unique index vs. &lt;code&gt;UNIQUE&lt;\/code&gt; constraint\">#<\/a><\/h2>\n\n\n\n<p>Both unique index and <a href=\"https:\/\/www.sqlservertutorial.net\/sql-server-basics\/sql-server-unique-constraint\/\"><code>UNIQUE<\/code> constraint<\/a> enforces the uniqueness of values in one or many columns. SQL Server validates duplicates in the same manner for both unique index and unique constraint.<\/p>\n\n\n\n<p>When you create a unique constraint, behind the scene, SQL Server creates a unique index associated with this constraint.<\/p>\n\n\n\n<p>However, creating a unique constraint on columns makes the objective of the unique index clear.<\/p>\n\n\n\n<p>In this tutorial, you have learned about the SQL Server unique index and how to create a unique index for one or many columns of a table.<\/p>\n<div class=\"helpful-block-content\" data-title=\"\">\n\t<header>\n\t\t<div class=\"wth-question\">Was this tutorial helpful?<\/div>\n\t\t<div class=\"wth-thumbs\">\n\t\t\t<button\n\t\t\t\tdata-post=\"1778\"\n\t\t\t\tdata-post-url=\"https:\/\/www.sqlservertutorial.net\/sql-server-indexes\/sql-server-unique-index\/\"\n\t\t\t\tdata-post-title=\"SQL Server Unique Index\"\n\t\t\t\tdata-response=\"1\"\n\t\t\t\tclass=\"wth-btn-rounded wth-yes-btn\"\n\t\t\t>\n\t\t\t\t<svg\n\t\t\t\t\txmlns=\"http:\/\/www.w3.org\/2000\/svg\"\n\t\t\t\t\tviewBox=\"0 0 24 24\"\n\t\t\t\t\tfill=\"none\"\n\t\t\t\t\tstroke=\"currentColor\"\n\t\t\t\t\tstroke-width=\"2\"\n\t\t\t\t\tstroke-linecap=\"round\"\n\t\t\t\t\tstroke-linejoin=\"round\"\n\t\t\t\t\tclass=\"feather feather-thumbs-up block w-full h-full\"\n\t\t\t\t>\n\t\t\t\t\t<path\n\t\t\t\t\t\td=\"M14 9V5a3 3 0 0 0-3-3l-4 9v11h11.28a2 2 0 0 0 2-1.7l1.38-9a2 2 0 0 0-2-2.3zM7 22H4a2 2 0 0 1-2-2v-7a2 2 0 0 1 2-2h3\"\n\t\t\t\t\t><\/path>\n\t\t\t\t<\/svg>\n\t\t\t\t<span class=\"sr-only\"> Yes <\/span>\n\t\t\t<\/button>\n\n\t\t\t<button\n\t\t\t\tdata-response=\"0\"\n\t\t\t\tdata-post=\"1778\"\n\t\t\t\tdata-post-url=\"https:\/\/www.sqlservertutorial.net\/sql-server-indexes\/sql-server-unique-index\/\"\n\t\t\t\tdata-post-title=\"SQL Server Unique Index\"\n\t\t\t\tclass=\"wth-btn-rounded wth-no-btn\"\n\t\t\t>\n\t\t\t\t<svg\n\t\t\t\t\txmlns=\"http:\/\/www.w3.org\/2000\/svg\"\n\t\t\t\t\tviewBox=\"0 0 24 24\"\n\t\t\t\t\tfill=\"none\"\n\t\t\t\t\tstroke=\"currentColor\"\n\t\t\t\t\tstroke-width=\"2\"\n\t\t\t\t\tstroke-linecap=\"round\"\n\t\t\t\t\tstroke-linejoin=\"round\"\n\t\t\t\t>\n\t\t\t\t\t<path\n\t\t\t\t\t\td=\"M10 15v4a3 3 0 0 0 3 3l4-9V2H5.72a2 2 0 0 0-2 1.7l-1.38 9a2 2 0 0 0 2 2.3zm7-13h2.67A2.31 2.31 0 0 1 22 4v7a2.31 2.31 0 0 1-2.33 2H17\"\n\t\t\t\t\t><\/path>\n\t\t\t\t<\/svg>\n\t\t\t\t<span class=\"sr-only\"> No <\/span>\n\t\t\t<\/button>\n\t\t<\/div>\n\t<\/header>\n\n\t<div class=\"wth-form hidden\">\n\t\t<div class=\"wth-form-wrapper\">\n\t\t\t<div class=\"wth-title\"><\/div>\n\t\t\t\n\t\t\t<textarea class=\"wth-message\"><\/textarea>\n\n\t\t\t<button class=\"btn btn-primary wth-btn-submit\">Send<\/button>\n\t\t\t<button class=\"btn wth-btn-cancel\">Cancel<\/button>\n\t\t\n\t\t<\/div>\n\t<\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>In this tutorial, you will learn about SQL Server unique indexes and how to use them to enforce the uniqueness of values in one or more columns of a table.<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":1746,"menu_order":3,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-1778","page","type-page","status-publish","hentry"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.5 - 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