{"id":1064,"date":"2018-10-22T20:22:48","date_gmt":"2018-10-22T13:22:48","guid":{"rendered":"http:\/\/www.sqlservertutorial.net\/?page_id=1064"},"modified":"2024-04-02T17:31:52","modified_gmt":"2024-04-02T10:31:52","slug":"sql-server-checksum_agg","status":"publish","type":"page","link":"https:\/\/www.sqlservertutorial.net\/sql-server-aggregate-functions\/sql-server-checksum_agg\/","title":{"rendered":"SQL Server CHECKSUM_AGG() Function"},"content":{"rendered":"\n<p><strong>Summary<\/strong>: in this tutorial, you will learn how to use the SQL Server <code>CHECKSUM_AGG()<\/code> function to detect the data changes in a column.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id='introduction-to-sql-server-checksum_agg-function'>Introduction to SQL Server CHECKSUM_AGG() function <a href=\"#introduction-to-sql-server-checksum_agg-function\" class=\"anchor\" id=\"introduction-to-sql-server-checksum_agg-function\" title=\"Anchor for Introduction to SQL Server CHECKSUM_AGG() function\">#<\/a><\/h2>\n\n\n\n<p>The <code>CHECKSUM_AGG()<\/code> function\u00a0is an <a href=\"https:\/\/www.sqlservertutorial.net\/sql-server-aggregate-functions\/\">aggregate\u00a0function<\/a> that returns the checksum of the values in a set.<\/p>\n\n\n\n<p>The following shows the syntax of the <code>CHECKSUM_AGG()<\/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\">CHECKSUM_AGG ( &#91; ALL | DISTINCT ] expression)  <\/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>ALL<\/code> instructs the function to return the checksum of all values including duplicates.<\/li>\n\n\n\n<li><code>DISTINCT<\/code> forces the function to calculate the checksum of distinct values.<\/li>\n\n\n\n<li><code>expression<\/code> is an integer expression. The function does not accept <a href=\"https:\/\/www.sqlservertutorial.net\/sql-server-basics\/sql-server-subquery\/\">subqueries<\/a> or <a href=\"https:\/\/www.sqlservertutorial.net\/sql-server-aggregate-functions\/\">aggregate functions<\/a>.<\/li>\n<\/ul>\n\n\n\n<p>The <code>CHECKSUM_AGG()<\/code> function ignores null values.<\/p>\n\n\n\n<p class=\"warning\">Because of the hashing algorithm, the\u00a0<code>CHECKSUM_AGG()<\/code>\u00a0function may return the same value with different input data. Therefore, you should use this function when your application can tolerate occasionally missing a change.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id='sql-server-checksum_agg-function-example'>SQL Server CHECKSUM_AGG() function example <a href=\"#sql-server-checksum_agg-function-example\" class=\"anchor\" id=\"sql-server-checksum_agg-function-example\" title=\"Anchor for SQL Server CHECKSUM_AGG() function example\">#<\/a><\/h2>\n\n\n\n<p>The following statement creates a new table called <code>sales.inventory<\/code> with the data retrieved from the <code>production.stocks<\/code> table\u00a0in the <a href=\"https:\/\/www.sqlservertutorial.net\/sql-server-sample-database\/\">sample database<\/a>. The new table stores products and their quantities:<\/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    product_id, \n    <span class=\"hljs-keyword\">SUM<\/span>(quantity) quantity\n<span class=\"hljs-keyword\">INTO<\/span> \n    sales.inventory\n<span class=\"hljs-keyword\">FROM<\/span>\n    production.stocks\n<span class=\"hljs-keyword\">GROUP<\/span> <span class=\"hljs-keyword\">BY<\/span> \n    product_id;<\/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>The following statement uses the <code>CHECKSUM_AGG()<\/code> function to get the aggregate checksum of the <code>quantity<\/code> column:<\/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    <span class=\"hljs-keyword\">CHECKSUM_AGG<\/span>(quantity) qty_checksum_agg\n<span class=\"hljs-keyword\">FROM<\/span>\n    sales.inventory;<\/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>Output:<\/p>\n\n\n<pre class=\"wp-block-code\"><span><code class=\"hljs\">qty_checksum_agg\n----------------\n29\n\n(1 row affected)<\/code><\/span><\/pre>\n\n\n<p>Let&#8217;s change the data in the <code>sales.inventory<\/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\">UPDATE<\/span> \n    sales.inventory\n<span class=\"hljs-keyword\">SET<\/span>\n    quantity = <span class=\"hljs-number\">10<\/span>\n<span class=\"hljs-keyword\">WHERE<\/span>\n    product_id = <span class=\"hljs-number\">1<\/span>;<\/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>And apply the <code>CHECKSUM_AGG()<\/code> function to the quantity column:<\/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\">SELECT<\/span> \n    <span class=\"hljs-keyword\">CHECKSUM_AGG<\/span>(quantity) qty_checksum_agg\n<span class=\"hljs-keyword\">FROM<\/span>\n    sales.inventory;<\/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>Output:<\/p>\n\n\n<pre class=\"wp-block-code\"><span><code class=\"hljs\">qty_checksum_agg\n----------------\n32\n\n(1 row affected)<\/code><\/span><\/pre>\n\n\n<p>The output indicates the result of the <code>CHECKSUM_AGG()<\/code> changes. It means that the data in the <code>quantity<\/code> column has been changed since the last checksum calculation.<\/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 <code>CHECKSUM_AGG()<\/code> function to detect the data changes in a column.<\/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=\"1064\"\n\t\t\t\tdata-post-url=\"https:\/\/www.sqlservertutorial.net\/sql-server-aggregate-functions\/sql-server-checksum_agg\/\"\n\t\t\t\tdata-post-title=\"SQL Server CHECKSUM_AGG() Function\"\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 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