{"id":10819,"date":"2023-10-08T07:07:59","date_gmt":"2023-10-08T14:07:59","guid":{"rendered":"https:\/\/www.mysqltutorial.org\/?page_id=10819"},"modified":"2023-10-08T08:39:53","modified_gmt":"2023-10-08T15:39:53","slug":"mysql-count-distinct","status":"publish","type":"page","link":"https:\/\/www.mysqltutorial.org\/mysql-aggregate-functions\/mysql-count-distinct\/","title":{"rendered":"MySQL COUNT DISTINCT"},"content":{"rendered":"\n<p><strong>Summary<\/strong>: in this tutorial, you will learn how to use the MySQL <code>COUNT<\/code> <code>DISTINCT<\/code> function to count the number of unique values in a specific column of a table.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Introduction to MySQL COUNT DISTINCT function<\/h2>\n\n\n\n<p>The <code>COUNT<\/code> <code>DISTINCT<\/code> allows you to <a href=\"https:\/\/www.mysqltutorial.org\/mysql-aggregate-functions\/mysql-count\/\">count<\/a> the number of unique values in a specific column of a table.<\/p>\n\n\n\n<p>Here&#8217;s the basic syntax for using the <code>COUNT<\/code> <code>DISTINCT<\/code> function:<\/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\">SELECT<\/span> <span class=\"hljs-keyword\">COUNT<\/span>(<span class=\"hljs-keyword\">DISTINCT<\/span> column_name)\n<span class=\"hljs-keyword\">FROM<\/span> table_name;<\/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><code>COUNT<\/code> <code>DISTINCT<\/code>: The function for counting unique values.<\/li>\n\n\n\n<li><code>column_name<\/code>: The name of the column for which you want to count distinct values.<\/li>\n\n\n\n<li><code>table_name<\/code>: The name of the table that contains the <code>column_name<\/code>.<\/li>\n<\/ul>\n\n\n\n<p>In practice, you use the <code>COUNT DISTINCT<\/code> when you want to find out how many unique values a present in a column.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">MySQL COUNT DISTINCT examples<\/h2>\n\n\n\n<p>Let&#8217;s take some examples of using the <code>COUNT DISTINCT<\/code> function. We&#8217;ll use the <code>employees<\/code> table from the <a href=\"https:\/\/www.mysqltutorial.org\/getting-started-with-mysql\/mysql-sample-database\/\">sample database<\/a> for the demonstration:<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img decoding=\"async\" src=\"https:\/\/www.mysqltutorial.org\/wp-content\/uploads\/2023\/10\/employees.svg\" alt=\"MySQL COUNT DISTINCT - employees table\" class=\"wp-image-10759\"\/><\/figure>\n\n\n\n<p>The following query retrieves first name, last name, and job title from the <code>employees<\/code> table:<\/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> firstName, lastName, jobTitle \n<span class=\"hljs-keyword\">FROM<\/span> employees;<\/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>Output:<\/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-comment\">-----------+-----------+----------------------+<\/span>\n| firstName | lastName  | jobTitle             |\n+<span class=\"hljs-comment\">-----------+-----------+----------------------+<\/span>\n| Diane     | Murphy    | President            |\n| Mary      | Patterson | VP Sales             |\n| Jeff      | Firrelli  | VP Marketing         |\n| William   | Patterson | Sales Manager (APAC) |\n| Gerard    | Bondur    | Sale Manager (EMEA)  |\n| Anthony   | Bow       | Sales Manager (NA)   |\n| Leslie    | Jennings  | Sales Rep            |\n| Leslie    | Thompson  | Sales Rep            |\n| Julie     | Firrelli  | Sales Rep            |\n| Steve     | Patterson | Sales Rep            |\n| Foon Yue  | Tseng     | Sales Rep            |\n| George    | Vanauf    | Sales Rep            |\n| Loui      | Bondur    | Sales Rep            |\n| Gerard    | Hernandez | Sales Rep            |\n| Pamela    | Castillo  | Sales Rep            |\n| Larry     | Bott      | Sales Rep            |\n| Barry     | Jones     | Sales Rep            |\n| Andy      | Fixter    | Sales Rep            |\n| Peter     | Marsh     | Sales Rep            |\n| Tom       | King      | Sales Rep            |\n| Mami      | Nishi     | Sales Rep            |\n| Yoshimi   | Kato      | Sales Rep            |\n| Martin    | Gerard    | Sales Rep            |\n+<span class=\"hljs-comment\">-----------+-----------+----------------------+<\/span>\n23 rows in <span class=\"hljs-keyword\">set<\/span> (<span class=\"hljs-number\">0.00<\/span> sec)<\/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 output indicates that the <code>employees<\/code> table has 23 rows.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">1) Using COUNT DISTINCT to get the number of unique job titles<\/h3>\n\n\n\n<p>The following example uses the <code>COUNT<\/code> <code>DISTINCT<\/code> function to get the unique number of job titles from the <code>jobTitle<\/code> column of the <code>employees<\/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\">SELECT<\/span>\n  <span class=\"hljs-keyword\">COUNT<\/span>(<span class=\"hljs-keyword\">DISTINCT<\/span> jobTitle) \n<span class=\"hljs-keyword\">from<\/span> \n  employees;<\/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>In this query: <\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><code>COUNT( DISTINCT jobTitle)<\/code>: Counts the number of distinct values in the <code>jobTitle<\/code> column.<\/li>\n\n\n\n<li><code>FROM employees<\/code>: Specifies the table from which to retrieve the data.<\/li>\n<\/ul>\n\n\n\n<p>When you execute the query, MySQL will return the following output:<\/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-comment\">--------------------------+<\/span>\n| count(distinct jobTitle) |\n+<span class=\"hljs-comment\">--------------------------+<\/span>\n|                        7 |\n+<span class=\"hljs-comment\">--------------------------+<\/span><\/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>You can use a <a href=\"https:\/\/www.mysqltutorial.org\/mysql-basics\/mysql-alias\/\">column alias<\/a> to assign a more meaningful name to the output column as follows:<\/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\">SELECT<\/span>\n  <span class=\"hljs-keyword\">COUNT<\/span>(<span class=\"hljs-keyword\">DISTINCT<\/span> jobTitle) uniqueJobTitleCount\n<span class=\"hljs-keyword\">from<\/span> \n  employees;<\/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>Output:<\/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-comment\">---------------------+<\/span>\n| uniqueJobTitleCount |\n+<span class=\"hljs-comment\">---------------------+<\/span>\n|                   7 |\n+<span class=\"hljs-comment\">---------------------+<\/span>\n1 row in <span class=\"hljs-keyword\">set<\/span> (<span class=\"hljs-number\">0.00<\/span> sec)<\/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<h3 class=\"wp-block-heading\">2) Using COUNT DISTINCT to get the number of unique first names<\/h3>\n\n\n\n<p>The following example uses the <code>COUNT<\/code> <code>DISTINCT<\/code> to get the number of unique first names of employees:<\/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\">SELECT<\/span>\n  <span class=\"hljs-keyword\">COUNT<\/span>(<span class=\"hljs-keyword\">DISTINCT<\/span> firstName) uniqueFirstNameCount\n<span class=\"hljs-keyword\">from<\/span> \n  employees;<\/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>Output:<\/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-comment\">----------------------+<\/span>\n| uniqueFirstNameCount |\n+<span class=\"hljs-comment\">----------------------+<\/span>\n|                   21 |\n+<span class=\"hljs-comment\">----------------------+<\/span>\n1 row in <span class=\"hljs-keyword\">set<\/span> (<span class=\"hljs-number\">0.00<\/span> sec)<\/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\">COUNT DISTINCT and NULL<\/h2>\n\n\n\n<p>In MySQL, the <code>COUNT DISTINCT<\/code> function does not count NULL values. It only counts unique, non-null values in the specified column. In other words, if a column has null values, the <code>COUNT DISTINCT<\/code> function will ignore NULL values from the count.<\/p>\n\n\n\n<p>Let&#8217;s take a look at the following example.<\/p>\n\n\n\n<p>First, <a href=\"https:\/\/www.mysqltutorial.org\/mysql-basics\/mysql-create-table\/\">create a new table<\/a> <code>contacts<\/code> that has two columns <code>id<\/code> and <code>name<\/code>:<\/p>\n\n\n<pre class=\"wp-block-code\"><span><code class=\"hljs\">CREATE TABLE contacts(\n   id INT AUTO_INCREMENT,\n   name VARCHAR(50),\n   PRIMARY KEY(id)\n);<\/code><\/span><\/pre>\n\n\n<p>Second, insert four rows into the <code>contacts<\/code> table:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-10\" data-shcb-language-name=\"PHP\" data-shcb-language-slug=\"php\"><span><code class=\"hljs language-php\">INSERT INTO contacts(name)\nVALUES (<span class=\"hljs-string\">\"John\"<\/span>), (<span class=\"hljs-string\">\"Jane\"<\/span>),(<span class=\"hljs-keyword\">NULL<\/span>), (<span class=\"hljs-string\">\"Jane\"<\/span>);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-10\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">PHP<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">php<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Third, select data from the <code>contacts<\/code> table:<\/p>\n\n\n<pre class=\"wp-block-code\"><span><code class=\"hljs\">SELECT * FROM contacts;<\/code><\/span><\/pre>\n\n\n<p>Output:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-11\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript\">+----+------+\n| id | name |\n+----+------+\n|  <span class=\"hljs-number\">1<\/span> | John |\n|  <span class=\"hljs-number\">2<\/span> | Jane |\n|  <span class=\"hljs-number\">3<\/span> | NULL |\n|  <span class=\"hljs-number\">4<\/span> | Jane |\n+----+------+\n<span class=\"hljs-number\">4<\/span> rows <span class=\"hljs-keyword\">in<\/span> <span class=\"hljs-keyword\">set<\/span> (0.00 sec)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-11\"><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<p>Finally, count the number of unique names in the <code>name<\/code> column of the <code>contacts<\/code> table:<\/p>\n\n\n<pre class=\"wp-block-code\"><span><code class=\"hljs\">SELECT COUNT(DISTINCT name)\nFROM contacts;<\/code><\/span><\/pre>\n\n\n<p>Output:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-12\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript\">+----------------------+\n| COUNT(DISTINCT name) |\n+----------------------+\n|                    <span class=\"hljs-number\">2<\/span> |\n+----------------------+\n<span class=\"hljs-number\">1<\/span> row <span class=\"hljs-keyword\">in<\/span> <span class=\"hljs-keyword\">set<\/span> (0.00 sec)<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-12\"><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<p>In this example, the <code>COUNT DISTINCT<\/code> function ignores the NULL value and only counts unique non-null values.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Summary<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Use MySQL <code>COUNT<\/code> <code>DISTINCT<\/code> function to count the number of unique values in a column of a table.<\/li>\n\n\n\n<li>The <code>COUNT DISTINCT<\/code> function ignores NULL values from the count.<\/li>\n<\/ul>\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=\"10819\"\n\t\t\t\tdata-post-url=\"https:\/\/www.mysqltutorial.org\/mysql-aggregate-functions\/mysql-count-distinct\/\"\n\t\t\t\tdata-post-title=\"MySQL COUNT DISTINCT\"\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 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