{"id":543,"date":"2016-04-14T01:52:25","date_gmt":"2016-04-14T01:52:25","guid":{"rendered":"https:\/\/sqltutorial.org\/?page_id=543"},"modified":"2025-02-08T00:59:32","modified_gmt":"2025-02-08T07:59:32","slug":"sql-primary-key","status":"publish","type":"page","link":"https:\/\/www.sqltutorial.org\/sql-primary-key\/","title":{"rendered":"SQL Primary Key"},"content":{"rendered":"\n<p><strong>Summary<\/strong>: in this tutorial, you will learn how to use the SQL <code>PRIMARY KEY<\/code> constraint to add a primary key to the table.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id='introduction-to-sql-primary-key-constraint'>Introduction to SQL Primary Key Constraint <a href=\"#introduction-to-sql-primary-key-constraint\" class=\"anchor\" id=\"introduction-to-sql-primary-key-constraint\" title=\"Anchor for Introduction to SQL Primary Key Constraint\">#<\/a><\/h2>\n\n\n\n<p>A primary key is a column or a set of columns that uniquely identifies each row in the table. A primary key ensures that each row is unique.<\/p>\n\n\n\n<p>A table includes one and only one primary key. If a primary key includes one column, that column is called a <strong>primary key column<\/strong>.<\/p>\n\n\n\n<p>If a primary key column includes two or more columns, these are primary key columns. The primary key is also known as a <strong>composite key<\/strong>.<\/p>\n\n\n\n<p>Here are the main characteristics of a primary key:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Uniqueness<\/strong>: Each value in the primary key column(s) must be unique.<\/li>\n\n\n\n<li><strong>Non-NULL<\/strong>: The primary key column cannot contain <code>NULL<\/code>.<\/li>\n\n\n\n<li><strong>Immutable<\/strong>: the values in the primary key column should not change.<\/li>\n<\/ul>\n\n\n\n<p>To create a primary key, you use the <code>PRIMARY KEY<\/code> constraint:<\/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\">column1 datatype PRIMARY KEY<\/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>For example, the following statement uses the <code>CREATE TABLE<\/code> statement to create a new table called <code>projects<\/code> with the <code>project_id<\/code> column as the primary key column:<\/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\">CREATE<\/span> <span class=\"hljs-keyword\">TABLE<\/span> projects (\n  project_id <span class=\"hljs-built_in\">INT<\/span> PRIMARY <span class=\"hljs-keyword\">KEY<\/span>,\n  project_name <span class=\"hljs-built_in\">VARCHAR<\/span>(<span class=\"hljs-number\">255<\/span>) <span class=\"hljs-keyword\">NOT<\/span> <span class=\"hljs-literal\">NULL<\/span>,\n  start_date <span class=\"hljs-built_in\">DATE<\/span> <span class=\"hljs-keyword\">NOT<\/span> <span class=\"hljs-literal\">NULL<\/span>,\n  end_date <span class=\"hljs-built_in\">DATE<\/span> <span class=\"hljs-keyword\">NOT<\/span> <span class=\"hljs-literal\">NULL<\/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<p><a href=\"https:\/\/www.sqltutorial.org\/playground\/?q=Q1JFQVRFIFRBQkxFIHByb2plY3RzICggcHJvamVjdF9pZCBJTlQgUFJJTUFSWSBLRVksIHByb2plY3RfbmFtZSBWQVJDSEFSKDI1NSkgTk9UIE5VTEwsIHN0YXJ0X2RhdGUgREFURSBOT1QgTlVMTCwgZW5kX2RhdGUgREFURSBOT1QgTlVMTCApOw%3D%3D\" target=\"_blank\" rel=\"noreferrer noopener\">Try it<\/a><\/p>\n\n\n\n<p>In this example, we use the <code>PRIMARY KEY<\/code> keywords in the <code>project_id<\/code> column&#8217;s definition. Typically the <code>PRIMARY KEY<\/code> constraint also enforces the <code>NOT NULL<\/code> constraint implicitly except <a href=\"https:\/\/www.sqlitetutorial.net\/sqlite-primary-key\/\" target=\"_blank\" rel=\"noreferrer noopener\">SQLite<\/a>.<\/p>\n\n\n\n<p>In this example, we define the <code>PRIMARY KEY<\/code> as a column constraint because we declare it in the primary key column&#8217;s definition.<\/p>\n\n\n\n<p>SQL allows you to define a primary key column as a table constraint by specifying it after the column list like this:<\/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\">CREATE<\/span> <span class=\"hljs-keyword\">TABLE<\/span> <span class=\"hljs-keyword\">IF<\/span> <span class=\"hljs-keyword\">NOT<\/span> <span class=\"hljs-keyword\">EXISTS<\/span> projects (\n  project_id <span class=\"hljs-built_in\">INT<\/span>,\n  project_name <span class=\"hljs-built_in\">VARCHAR<\/span>(<span class=\"hljs-number\">255<\/span>) <span class=\"hljs-keyword\">NOT<\/span> <span class=\"hljs-literal\">NULL<\/span>,\n  start_date <span class=\"hljs-built_in\">DATE<\/span> <span class=\"hljs-keyword\">NOT<\/span> <span class=\"hljs-literal\">NULL<\/span>,\n  end_date <span class=\"hljs-built_in\">DATE<\/span> <span class=\"hljs-keyword\">NOT<\/span> <span class=\"hljs-literal\">NULL<\/span>,\n  PRIMARY <span class=\"hljs-keyword\">KEY<\/span> (project_id)\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><a href=\"https:\/\/www.sqltutorial.org\/playground\/?q=Q1JFQVRFIFRBQkxFIElGIE5PVCBFWElTVFMgcHJvamVjdHMgKCBwcm9qZWN0X2lkIElOVCwgcHJvamVjdF9uYW1lIFZBUkNIQVIoMjU1KSBOT1QgTlVMTCwgc3RhcnRfZGF0ZSBEQVRFIE5PVCBOVUxMLCBlbmRfZGF0ZSBEQVRFIE5PVCBOVUxMLCBQUklNQVJZIEtFWSAocHJvamVjdF9pZCkgKTs%3D\" target=\"_blank\" rel=\"noreferrer noopener\">Try it<\/a><\/p>\n\n\n\n<p>This syntax is more suitable for defining a primary key with two or more columns.<\/p>\n\n\n\n<p>For example, the following statement creates a table called <code>project_assignments<\/code> that stores the projects assigned to employees:<\/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\">TABLE<\/span> project_assignments (\n  project_id <span class=\"hljs-built_in\">INT<\/span>,\n  employee_id <span class=\"hljs-built_in\">INT<\/span>,\n  assigned_date <span class=\"hljs-built_in\">DATE<\/span> <span class=\"hljs-keyword\">NOT<\/span> <span class=\"hljs-literal\">NULL<\/span>,\n  PRIMARY <span class=\"hljs-keyword\">KEY<\/span> (project_id, employee_id)\n);<\/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><a href=\"https:\/\/www.sqltutorial.org\/playground\/?q=Q1JFQVRFIFRBQkxFIHByb2plY3RfYXNzaWdubWVudHMgKCBwcm9qZWN0X2lkIElOVCwgZW1wbG95ZWVfaWQgSU5ULCBhc3NpZ25lZF9kYXRlIERBVEUgTk9UIE5VTEwsIFBSSU1BUlkgS0VZIChwcm9qZWN0X2lkLCBlbXBsb3llZV9pZCkgKTs%3D\" target=\"_blank\" rel=\"noreferrer noopener\">Try it<\/a><\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id='primary-key-constraint-names'>Primary Key Constraint Names <a href=\"#primary-key-constraint-names\" class=\"anchor\" id=\"primary-key-constraint-names\" title=\"Anchor for Primary Key Constraint Names\">#<\/a><\/h2>\n\n\n\n<p>When defining a primary key constraint, you can assign it a name using the <code>CONSTRAINT<\/code> clause:<\/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\">CONSTRAINT constraint_name\nPRIMARY KEY(column1, column2, ...)<\/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>If you don&#8217;t provide a name for the <code>PRIMARY KEY<\/code> constraint, the database system will generate a default name for it.<\/p>\n\n\n\n<p>This default name may vary depending on databse systems. The following table shows the default names for the primary key constraints in different database systems:<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>Database System<\/th><th>Default Primary Key Constraint Name<\/th><\/tr><\/thead><tbody><tr><td>SQL Server<\/td><td><code>PK_TableName_HexadecimalSequence<\/code><\/td><\/tr><tr><td>MySQL<\/td><td><code>PRIMARY<\/code><\/td><\/tr><tr><td>PostgreSQL<\/td><td><code>TableName_pkey<\/code><\/td><\/tr><tr><td>Oracle<\/td><td><code>SYS_Cn<\/code> (where <code>n<\/code> is a number)<\/td><\/tr><tr><td>SQLite<\/td><td><code>sqlite_autoindex_TableName_n<\/code><\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p>The following example creates a table called <code>project_milestones<\/code> to store the project milestones:<\/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\">TABLE<\/span> project_milestones (\n  milestone_id <span class=\"hljs-built_in\">INT<\/span>,\n  project_id <span class=\"hljs-built_in\">INT<\/span> <span class=\"hljs-keyword\">NOT<\/span> <span class=\"hljs-literal\">NULL<\/span>,\n  milestone_name <span class=\"hljs-built_in\">VARCHAR<\/span>(<span class=\"hljs-number\">255<\/span>) <span class=\"hljs-keyword\">NOT<\/span> <span class=\"hljs-literal\">NULL<\/span>,\n  <span class=\"hljs-keyword\">CONSTRAINT<\/span> project_milestones_pk PRIMARY <span class=\"hljs-keyword\">KEY<\/span> (milestone_id)\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>In this example, we explicitly name the primary key constraint as <code>project_milestones_pk<\/code>.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id='removing-a-primary-key-from-a-table'>Removing a primary key from a table <a href=\"#removing-a-primary-key-from-a-table\" class=\"anchor\" id=\"removing-a-primary-key-from-a-table\" title=\"Anchor for Removing a primary key from a table\">#<\/a><\/h2>\n\n\n\n<p>To drop a primary key from a table, you use the <code>ALTER TABLE<\/code> statement:<\/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\">ALTER<\/span> <span class=\"hljs-keyword\">TABLE<\/span> table_name\n<span class=\"hljs-keyword\">DROP<\/span> <span class=\"hljs-keyword\">CONSTRAINT<\/span> primary_key_constraint;<\/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>In this syntax:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>First, specify the table name from which you want to remove the primary key.<\/li>\n\n\n\n<li>Second, provide the primary key constraint name.<\/li>\n<\/ul>\n\n\n\n<p>To find the primary key constraint name, you can search for it using the specific command in your database system.<\/p>\n\n\n\n<p>For example, the following statement drops the primary key from the <code>project_milestones<\/code> table:<\/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\">ALTER<\/span> <span class=\"hljs-keyword\">TABLE<\/span> project_milestones \n<span class=\"hljs-keyword\">DROP<\/span> <span class=\"hljs-keyword\">CONSTRAINT<\/span> project_milestones_pk ;<\/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><a href=\"https:\/\/www.sqltutorial.org\/playground\/?q=QUxURVIgVEFCTEUgcHJvamVjdF9taWxlc3RvbmVzIERST1AgQ09OU1RSQUlOVCBwcm9qZWN0X21pbGVzdG9uZXNfcGs7\" target=\"_blank\" rel=\"noreferrer noopener\">Try it<\/a><\/p>\n\n\n\n<p>In this statement, the <code>project_milestones_pk<\/code> is the constraint name of the primary key of the <code>project_milestones<\/code> table.<\/p>\n\n\n\n<p>Some database systems do not require a primary constraint name such as MySQL. The syntax for dropping a primary key constraint is as follows:<\/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\">ALTER<\/span> <span class=\"hljs-keyword\">TABLE<\/span> table_name\n<span class=\"hljs-keyword\">DROP<\/span> PRIMARY <span class=\"hljs-keyword\">KEY<\/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<h2 class=\"wp-block-heading\" id='adding-the-primary-key-to-an-existing-table'>Adding the primary key to an existing table <a href=\"#adding-the-primary-key-to-an-existing-table\" class=\"anchor\" id=\"adding-the-primary-key-to-an-existing-table\" title=\"Anchor for Adding the primary key to an existing table\">#<\/a><\/h2>\n\n\n\n<p>SQL allows you to create a table without a primary key. However, it is not a good practice.<\/p>\n\n\n\n<p>To add a primary key to an existing table, you use the <code>ALTER TABLE<\/code> statement:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-10\" data-shcb-language-name=\"SQL (Structured Query Language)\" data-shcb-language-slug=\"sql\"><span><code class=\"hljs language-sql\"><span class=\"hljs-keyword\">ALTER<\/span> <span class=\"hljs-keyword\">TABLE<\/span> table_name\n<span class=\"hljs-keyword\">ADD<\/span> <span class=\"hljs-keyword\">CONSTRAINT<\/span> constraint_name \nPRIMARY <span class=\"hljs-keyword\">KEY<\/span> (column1, column2, ...);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-10\"><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 table you want to ad a primary key.<\/li>\n\n\n\n<li>Second, optionally provide a constraint name.<\/li>\n\n\n\n<li>Third, list one or more primary key columns in the <code>PRIMARY KEY<\/code> clause.<\/li>\n<\/ul>\n\n\n\n<p>For example, the following statement adds a primary key constraint to the <code>project_milestones<\/code> table:<\/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\">ALTER<\/span> <span class=\"hljs-keyword\">TABLE<\/span> project_milestones\n<span class=\"hljs-keyword\">ADD<\/span> PRIMARY <span class=\"hljs-keyword\">KEY<\/span> (milestone_id);<\/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><a href=\"https:\/\/www.sqltutorial.org\/playground\/?q=QUxURVIgVEFCTEUgcHJvamVjdF9taWxlc3RvbmVzIEFERCBQUklNQVJZIEtFWSAobWlsZXN0b25lX2lkKTs%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>A primary key is one column or a set of columns uniquely identifying each row in a table.<\/li>\n\n\n\n<li>Use the <code>PRIMARY KEY<\/code> constraint to define a primary key for a table.<\/li>\n\n\n\n<li>Use the <code>ALTER TABLE .... ADD PRIMARY KEY<\/code>statement to add a primary key to an existing table.<\/li>\n\n\n\n<li>Use the <code>ALTER TABLE ... DROP CONSTRAINT<\/code> statement to remove a primary key from a table.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id='databases'>Databases <a href=\"#databases\" class=\"anchor\" id=\"databases\" title=\"Anchor for Databases\">#<\/a><\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li><a href=\"https:\/\/www.pgtutorial.com\/postgresql-tutorial\/postgresql-primary-key\/\" target=\"_blank\" rel=\"noreferrer noopener\">PostgreSQL Primary Key <\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/www.mysqltutorial.org\/mysql-basics\/mysql-primary-key\/\" target=\"_blank\" rel=\"noreferrer noopener\">MySQL Primary Key<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/www.mariadbtutorial.com\/mariadb-basics\/mariadb-primary-key\/\" target=\"_blank\" rel=\"noreferrer noopener\">MariaDB Primary Key<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/www.oracletutorial.com\/oracle-basics\/oracle-primary-key\/\" target=\"_blank\" rel=\"noreferrer noopener\">Oracle Primary Key<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/www.db2tutorial.com\/db2-basics\/db2-primary-key\/\" target=\"_blank\" rel=\"noreferrer noopener\">Db2 Primary Key<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/www.sqlitetutorial.net\/sqlite-primary-key\/\" target=\"_blank\" rel=\"noreferrer noopener\">SQLite Primary Key<\/a><\/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=primary-key\"\n  height=\"700\"\n  width=\"600\"\n  class=\"iframe\"\n><\/iframe>\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=\"543\"\n\t\t\t\tdata-post-url=\"https:\/\/www.sqltutorial.org\/sql-primary-key\/\"\n\t\t\t\tdata-post-title=\"SQL Primary Key\"\n\t\t\t\tdata-response=\"1\"\n\t\t\t\tclass=\"wth-btn-rounded 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