{"id":1030,"date":"2024-12-17T10:58:40","date_gmt":"2024-12-17T03:58:40","guid":{"rendered":"https:\/\/www.pgtutorial.com\/?page_id=1030"},"modified":"2025-01-05T19:56:45","modified_gmt":"2025-01-05T12:56:45","slug":"postgresql-var_pop","status":"publish","type":"page","link":"https:\/\/www.pgtutorial.com\/postgresql-aggregate-functions\/postgresql-var_pop\/","title":{"rendered":"PostgreSQL VAR_POP Aggregate Function"},"content":{"rendered":"\n<p><strong>Summary<\/strong>: in this tutorial, you&#8217;ll learn how to use the PostgreSQL <code>VAR_POP<\/code> aggregate function to calculate the population variance of a set of values.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id='getting-started-with-the-postgresql-var_pop-aggregate-function'>Getting Started with the PostgreSQL VAR_POP aggregate function <a href=\"#getting-started-with-the-postgresql-var_pop-aggregate-function\" class=\"anchor\" id=\"getting-started-with-the-postgresql-var_pop-aggregate-function\" title=\"Anchor for Getting Started with the PostgreSQL VAR_POP aggregate function\">#<\/a><\/h2>\n\n\n\n<p>A population variance measures how much values differ from the mean (or average). Population variance is an essential indicator because it reflects the spread or dispersion of the data points.<\/p>\n\n\n\n<p>The following steps illustrate how to calculate the population variance:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>First, calculate the average (or mean) of all the values.<\/li>\n\n\n\n<li>Next, find each value&#8217;s difference (or deviation) from the mean.<\/li>\n\n\n\n<li>Then, square each deviation to ensure all the values are positive.<\/li>\n\n\n\n<li>After that, sum all the squared deviations.<\/li>\n\n\n\n<li>Finally, divide the sum by the number of values to get the population variance.<\/li>\n<\/ul>\n\n\n\n<p>The following shows the formula to calculate the population variance:<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"256\" height=\"85\" src=\"https:\/\/www.pgtutorial.com\/wp-content\/uploads\/2024\/12\/postgresql-var_pop-function.png\" alt=\"postgresql var_pop function\" class=\"wp-image-1033\"\/><\/figure>\n\n\n\n<p>where:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\u03c3<sup>2<\/sup>&nbsp;is the population variance.<\/li>\n\n\n\n<li>x<sub>i<\/sub>&nbsp;is each individual value.<\/li>\n\n\n\n<li>\u03bc is the population mean.<\/li>\n\n\n\n<li>N is the number of values in the population.<\/li>\n<\/ul>\n\n\n\n<p>PostgreSQL offers the <code>VAR_POP<\/code> aggregate function to calculate the population variance.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id='syntax'>Syntax <a href=\"#syntax\" class=\"anchor\" id=\"syntax\" title=\"Anchor for Syntax\">#<\/a><\/h3>\n\n\n\n<p>Here&#8217;s the syntax of the <code>VAR_POP<\/code> aggregate function:<\/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\">SELECT<\/span>\n  VAR_POP(column1)\n<span class=\"hljs-keyword\">FROM<\/span>\n  <span class=\"hljs-built_in\">table_name<\/span>;<\/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>In this syntax, the <code>VAR_POP<\/code> function takes all values in <code>column1<\/code> and returns the population variance. <\/p>\n\n\n\n<p>The <code>VAR_POP<\/code> function ignores <code>NULL<\/code> in <code>column1<\/code>. It only takes non-NULL to calculate the population variance. <\/p>\n\n\n\n<p>If <code>column1<\/code> has no value, i.e., no rows to aggregate, the <code>VAR_POP<\/code> function returns <code>NULL<\/code>.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id='calculating-the-population-variance-for-groups'>Calculating the Population Variance for Groups <a href=\"#calculating-the-population-variance-for-groups\" class=\"anchor\" id=\"calculating-the-population-variance-for-groups\" title=\"Anchor for Calculating the Population Variance for Groups\">#<\/a><\/h3>\n\n\n\n<p>To calculate the population variance for groups, you can use the <code>VAR_POP<\/code> function with the <code><a href=\"https:\/\/www.pgtutorial.com\/postgresql-tutorial\/postgresql-group-by\/\">GROUP BY<\/a><\/code> clause:<\/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\">SELECT<\/span>\n  column2,\n  VAR_POP(column1)\n<span class=\"hljs-keyword\">FROM<\/span>\n  <span class=\"hljs-built_in\">table_name<\/span>\n<span class=\"hljs-keyword\">GROUP<\/span> <span class=\"hljs-keyword\">BY<\/span>\n  column2;<\/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>In this syntax:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The <code>GROUP BY<\/code> clause divides the rows in the <code>table_name<\/code> by the values in <code>column2<\/code> into groups.<\/li>\n\n\n\n<li>The <code>VAR_POP<\/code> function calculates the population variance for values in <code>column1<\/code> in each group.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id='postgresql-var_pop-aggregate-function-examples'>PostgreSQL VAR_POP Aggregate Function Examples <a href=\"#postgresql-var_pop-aggregate-function-examples\" class=\"anchor\" id=\"postgresql-var_pop-aggregate-function-examples\" title=\"Anchor for PostgreSQL VAR_POP Aggregate Function Examples\">#<\/a><\/h2>\n\n\n\n<p>Let&#8217;s explore using the <code>VAR_POP<\/code> function with practical examples based on an <code>inventory<\/code> database.<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"144\" height=\"139\" src=\"https:\/\/www.pgtutorial.com\/wp-content\/uploads\/2024\/12\/inventories.png\" alt=\"\" class=\"wp-image-1046\"\/><\/figure>\n\n\n\n<h3 class=\"wp-block-heading\" id='calculating-the-population-variance-of-inventory'>Calculating the Population Variance of Inventory <a href=\"#calculating-the-population-variance-of-inventory\" class=\"anchor\" id=\"calculating-the-population-variance-of-inventory\" title=\"Anchor for Calculating the Population Variance of Inventory\">#<\/a><\/h3>\n\n\n\n<p>The following statement uses the <code>VAR_POP<\/code> function to calculate the population variance of product quantity in the inventory:<\/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\">SELECT<\/span>\n  VAR_POP(quantity) <span class=\"hljs-keyword\">AS<\/span> population_variance\n<span class=\"hljs-keyword\">FROM<\/span>\n  inventories;<\/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><a href=\"https:\/\/www.pgtutorial.com\/playground\/?q=U0VMRUNUIFZBUl9QT1AocXVhbnRpdHkpIEFTIHBvcHVsYXRpb25fdmFyaWFuY2UgRlJPTSBpbnZlbnRvcmllczs%3D\" target=\"_blank\" rel=\"noreferrer noopener\">Try it<br><\/a><\/p>\n\n\n\n<p>Output: <\/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\">  population_variance\n<span class=\"hljs-comment\">-----------------------<\/span>\n <span class=\"hljs-number\">4608.6400000000000000<\/span><\/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>The output sample variance indicates how much the inventory quantities differ from the mean.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id='calculating-the-population-variance-of-inventory-by-warehouse'>Calculating the Population Variance of Inventory by Warehouse <a href=\"#calculating-the-population-variance-of-inventory-by-warehouse\" class=\"anchor\" id=\"calculating-the-population-variance-of-inventory-by-warehouse\" title=\"Anchor for Calculating the Population Variance of Inventory by Warehouse\">#<\/a><\/h3>\n\n\n\n<p>The following statement uses the <code>VAR_POP<\/code> function with the <code>GROUP BY<\/code> clause to calculate the population variance of inventory by warehouse:<\/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\">SELECT<\/span>\n  warehouse_id,\n  ROUND(VAR_POP(quantity), <span class=\"hljs-number\">0<\/span>) <span class=\"hljs-keyword\">AS<\/span> population_variance\n<span class=\"hljs-keyword\">FROM<\/span>\n  inventories\n<span class=\"hljs-keyword\">GROUP<\/span> <span class=\"hljs-keyword\">BY<\/span>\n  warehouse_id;<\/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<p><a href=\"https:\/\/www.pgtutorial.com\/playground\/?q=U0VMRUNUIHdhcmVob3VzZV9pZCwgUk9VTkQoVkFSX1BPUChxdWFudGl0eSksIDApIEFTIHBvcHVsYXRpb25fdmFyaWFuY2UgRlJPTSBpbnZlbnRvcmllcyBHUk9VUCBCWSB3YXJlaG91c2VfaWQ7\" target=\"_blank\" rel=\"noreferrer noopener\">Try it<\/a><br>Output: <\/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\"> warehouse_id | population_variance\n<span class=\"hljs-comment\">--------------+---------------------<\/span>\n            <span class=\"hljs-number\">3<\/span> |                <span class=\"hljs-number\">3994<\/span>\n            <span class=\"hljs-number\">2<\/span> |                <span class=\"hljs-number\">3686<\/span>\n            <span class=\"hljs-number\">1<\/span> |                <span class=\"hljs-number\">5889<\/span><\/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>In this example:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>First, the <code>GROUP BY<\/code> clause divides the rows by the <code>warehouse_id<\/code> into groups.<\/li>\n\n\n\n<li>The <code>VAR_POP<\/code> function calculates the population variance for inventory in each group.<\/li>\n<\/ul>\n\n\n\n<p>If you want to retrieve the category name, you can <a href=\"https:\/\/www.pgtutorial.com\/postgresql-tutorial\/postgresql-inner-join\/\">join<\/a> the <code>inventories<\/code> table with the <code>warehouses<\/code> table:<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"344\" height=\"139\" src=\"https:\/\/www.pgtutorial.com\/wp-content\/uploads\/2024\/12\/inventories-warehouses.png\" alt=\"\" class=\"wp-image-1045\" srcset=\"https:\/\/www.pgtutorial.com\/wp-content\/uploads\/2024\/12\/inventories-warehouses.png 344w, https:\/\/www.pgtutorial.com\/wp-content\/uploads\/2024\/12\/inventories-warehouses-300x121.png 300w\" sizes=\"auto, (max-width: 344px) 100vw, 344px\" \/><\/figure>\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\">SELECT<\/span>\n  warehouse_name,\n  ROUND(VAR_POP(quantity), <span class=\"hljs-number\">0<\/span>) <span class=\"hljs-keyword\">AS<\/span> population_variance\n<span class=\"hljs-keyword\">FROM<\/span>\n  inventories\n  <span class=\"hljs-keyword\">JOIN<\/span> warehouses <span class=\"hljs-keyword\">USING<\/span> (warehouse_id)\n<span class=\"hljs-keyword\">GROUP<\/span> <span class=\"hljs-keyword\">BY<\/span>\n  warehouse_name;<\/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\/?q=U0VMRUNUIHdhcmVob3VzZV9uYW1lLCBST1VORChWQVJfUE9QKHF1YW50aXR5KSwgMCkgQVMgcG9wdWxhdGlvbl92YXJpYW5jZSBGUk9NIGludmVudG9yaWVzIEpPSU4gd2FyZWhvdXNlcyBVU0lORyAod2FyZWhvdXNlX2lkKSBHUk9VUCBCWSB3YXJlaG91c2VfbmFtZTs%3D\" target=\"_blank\" rel=\"noreferrer noopener\">Try it<\/a><br>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\">     warehouse_name      | population_variance\n<span class=\"hljs-comment\">-------------------------+---------------------<\/span>\n San Francisco Warehouse |                <span class=\"hljs-number\">3686<\/span>\n Los Angeles Warehouse   |                <span class=\"hljs-number\">3994<\/span>\n San Jose Warehouse      |                <span class=\"hljs-number\">5889<\/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>The output shows the variability of inventory within each warehouse. The warehouse with a higher population variance might have a broader range of inventory quantity.<\/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>VAR_POP<\/code> aggregate function to calculate the sample variance of a set of values.<\/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=var_pop\"\n  height=\"700\"\n  width=\"600\"\n  class=\"iframe\"\n><\/iframe>\n\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 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