{"id":1253,"date":"2024-12-24T19:22:40","date_gmt":"2024-12-24T12:22:40","guid":{"rendered":"https:\/\/www.pgtutorial.com\/?page_id=1253"},"modified":"2025-01-05T21:27:42","modified_gmt":"2025-01-05T14:27:42","slug":"postgresql-count-window-function","status":"publish","type":"page","link":"https:\/\/www.pgtutorial.com\/postgresql-window-functions\/postgresql-count-window-function\/","title":{"rendered":"PostgreSQL COUNT Window Function"},"content":{"rendered":"\n<p><strong>Summary<\/strong>: in this tutorial, you&#8217;ll learn how to use the PostgreSQL <code>COUNT()<\/code> window function to count the number of rows within a partition.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id='introduction-to-postgresql-count-window-function'>Introduction to PostgreSQL COUNT() Window Function <a href=\"#introduction-to-postgresql-count-window-function\" class=\"anchor\" id=\"introduction-to-postgresql-count-window-function\" title=\"Anchor for Introduction to PostgreSQL COUNT() Window Function\">#<\/a><\/h2>\n\n\n\n<p>In PostgreSQL, the <code>COUNT()<\/code> window function returns the number of rows within a partition. Here&#8217;s the syntax of the <code>COUNT()<\/code> window 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\">COUNT(<span class=\"hljs-keyword\">value<\/span>) <span class=\"hljs-keyword\">OVER<\/span> (\n\u00a0 \u00a0&#91;<span class=\"hljs-keyword\">PARTITION<\/span> <span class=\"hljs-keyword\">BY<\/span> partition_expression]\n\u00a0 \u00a0&#91;<span class=\"hljs-keyword\">ORDER<\/span> <span class=\"hljs-keyword\">BY<\/span> sort_expression]\n)<\/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:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><code>value<\/code> is a column in which you want to count the values. If you use star (<code>*<\/code>) the <code>COUNT()<\/code> function will count the rows.<\/li>\n\n\n\n<li>The <code>OVER<\/code> defines the window frame where the <code>COUNT()<\/code> function applies.<\/li>\n\n\n\n<li><code>PARTITION BY<\/code> divides the result set into partitions by the <code>partition_expression<\/code>. The <code>partition_expression<\/code> can be one or more columns. If you omit the <code>PARTITION BY<\/code> clause, the <code>COUNT()<\/code> returns total number of rows in the result set.<\/li>\n\n\n\n<li><code>ORDER BY<\/code> clause determines the order of rows within each partition.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id='postgresql-count-window-function-examples'>PostgreSQL COUNT Window Function examples <a href=\"#postgresql-count-window-function-examples\" class=\"anchor\" id=\"postgresql-count-window-function-examples\" title=\"Anchor for PostgreSQL COUNT Window Function examples\">#<\/a><\/h2>\n\n\n\n<p>Let&#8217;s take some examples of using the PostgreSQL <code>COUNT()<\/code> window function with the <code>products<\/code> table:<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"159\" height=\"254\" src=\"https:\/\/www.pgtutorial.com\/wp-content\/uploads\/2024\/12\/products.png\" alt=\"PostgreSQL COUNT Window Function\" class=\"wp-image-1051\"\/><\/figure>\n\n\n\n<h3 class=\"wp-block-heading\" id='counting-products'>Counting products <a href=\"#counting-products\" class=\"anchor\" id=\"counting-products\" title=\"Anchor for Counting products\">#<\/a><\/h3>\n\n\n\n<p>The following example uses the <code>COUNT()<\/code> window function to return the number of products along with the current product:<\/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  product_id,\n  product_name,\n  COUNT(*) <span class=\"hljs-keyword\">OVER<\/span> () <span class=\"hljs-keyword\">AS<\/span> total_products\n<span class=\"hljs-keyword\">FROM<\/span>\n  products;<\/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><a href=\"https:\/\/www.pgtutorial.com\/playground\/?q=U0VMRUNUIHByb2R1Y3RfaWQsIHByb2R1Y3RfbmFtZSwgQ09VTlQoKikgT1ZFUiAoKSBBUyB0b3RhbF9wcm9kdWN0cyBGUk9NIHByb2R1Y3RzOw%3D%3D\" target=\"_blank\" rel=\"noreferrer noopener\">Try it<\/a><\/p>\n\n\n\n<p>Output:<\/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\"> product_id |        product_name        | total_products\n<span class=\"hljs-comment\">------------+----------------------------+----------------<\/span>\n          <span class=\"hljs-number\">1<\/span> | Samsung Galaxy S24         |             <span class=\"hljs-number\">25<\/span>\n          <span class=\"hljs-number\">2<\/span> | Apple iPhone <span class=\"hljs-number\">15<\/span>            |             <span class=\"hljs-number\">25<\/span>\n          <span class=\"hljs-number\">3<\/span> | Huawei Mate <span class=\"hljs-number\">60<\/span>             |             <span class=\"hljs-number\">25<\/span>\n          <span class=\"hljs-number\">4<\/span> | Xiaomi Mi <span class=\"hljs-number\">14<\/span>               |             <span class=\"hljs-number\">25<\/span>\n          <span class=\"hljs-number\">5<\/span> | Sony Xperia <span class=\"hljs-number\">1<\/span> VI           |             <span class=\"hljs-number\">25<\/span>\n          <span class=\"hljs-number\">6<\/span> | Samsung Galaxy Z Fold <span class=\"hljs-number\">5<\/span>    |             <span class=\"hljs-number\">25<\/span>\n          <span class=\"hljs-number\">7<\/span> | Apple iPhone <span class=\"hljs-number\">15<\/span> Pro Max    |             <span class=\"hljs-number\">25<\/span>\n          <span class=\"hljs-number\">8<\/span> | Samsung Galaxy Tab S9      |             <span class=\"hljs-number\">25<\/span>\n          <span class=\"hljs-number\">9<\/span> | Apple iPad Pro <span class=\"hljs-number\">12.9<\/span>        |             <span class=\"hljs-number\">25<\/span>\n         <span class=\"hljs-number\">10<\/span> | Apple AirPods Pro <span class=\"hljs-number\">3<\/span>        |             <span class=\"hljs-number\">25<\/span>\n         <span class=\"hljs-number\">11<\/span> | Samsung Galaxy Buds Pro <span class=\"hljs-number\">2<\/span>  |             <span class=\"hljs-number\">25<\/span>\n         <span class=\"hljs-number\">12<\/span> | Apple Watch Series <span class=\"hljs-number\">9<\/span>       |             <span class=\"hljs-number\">25<\/span>\n         <span class=\"hljs-number\">13<\/span> | Samsung Galaxy Watch <span class=\"hljs-number\">6<\/span>     |             <span class=\"hljs-number\">25<\/span>\n         <span class=\"hljs-number\">14<\/span> | LG OLED TV C3              |             <span class=\"hljs-number\">25<\/span>\n         <span class=\"hljs-number\">15<\/span> | Sony Bravia XR A95K        |             <span class=\"hljs-number\">25<\/span>\n         <span class=\"hljs-number\">16<\/span> | Samsung QN900C Neo QLED    |             <span class=\"hljs-number\">25<\/span>\n         <span class=\"hljs-number\">17<\/span> | LG G3 OLED                 |             <span class=\"hljs-number\">25<\/span>\n         <span class=\"hljs-number\">18<\/span> | Sony HT-A7000 Soundbar     |             <span class=\"hljs-number\">25<\/span>\n         <span class=\"hljs-number\">19<\/span> | Bose SoundLink Max         |             <span class=\"hljs-number\">25<\/span>\n         <span class=\"hljs-number\">20<\/span> | Dell XPS <span class=\"hljs-number\">15<\/span>                |             <span class=\"hljs-number\">25<\/span>\n         <span class=\"hljs-number\">21<\/span> | HP Spectre x360            |             <span class=\"hljs-number\">25<\/span>\n         <span class=\"hljs-number\">22<\/span> | Microsoft Surface Laptop <span class=\"hljs-number\">5<\/span> |             <span class=\"hljs-number\">25<\/span>\n         <span class=\"hljs-number\">23<\/span> | Lenovo ThinkPad X1 Carbon  |             <span class=\"hljs-number\">25<\/span>\n         <span class=\"hljs-number\">24<\/span> | Apple iMac <span class=\"hljs-number\">24<\/span>\"             |             25\n         25 | Dell Inspiron 27           |             25<\/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>In this query, <code>COUNT(*) OVER ()<\/code> returns the number of rows in the <code>products<\/code> table. The result set includes each product along with the total number of products.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id='counting-products-for-each-brand'>Counting products for each brand <a href=\"#counting-products-for-each-brand\" class=\"anchor\" id=\"counting-products-for-each-brand\" title=\"Anchor for Counting products for each brand\">#<\/a><\/h2>\n\n\n\n<p>The following <a href=\"https:\/\/www.pgtutorial.com\/postgresql-tutorial\/postgresql-select\/\">query<\/a> uses the <code>COUNT()<\/code> window function with <code>PARTITION BY<\/code> clause to return the number of products for each brand:<\/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\"><span class=\"hljs-keyword\">SELECT<\/span>\n  brand_id,\n  product_id,\n  product_name,\n  COUNT(*) <span class=\"hljs-keyword\">OVER<\/span> (<span class=\"hljs-keyword\">PARTITION<\/span> <span class=\"hljs-keyword\">BY<\/span> brand_id) <span class=\"hljs-keyword\">AS<\/span> products_per_brand\n<span class=\"hljs-keyword\">FROM<\/span>\n  products;<\/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><a href=\"https:\/\/www.pgtutorial.com\/playground\/?q=U0VMRUNUIGJyYW5kX2lkLCBwcm9kdWN0X2lkLCBwcm9kdWN0X25hbWUsIENPVU5UKCopIE9WRVIgKFBBUlRJVElPTiBCWSBicmFuZF9pZCkgQVMgcHJvZHVjdHNfcGVyX2JyYW5kIEZST00gcHJvZHVjdHM7\" target=\"_blank\" rel=\"noreferrer noopener\">Try it<\/a><\/p>\n\n\n\n<p>Output:<\/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\"> brand_id | product_id |        product_name        | products_per_brand\n<span class=\"hljs-comment\">----------+------------+----------------------------+--------------------<\/span>\n        <span class=\"hljs-number\">1<\/span> |          <span class=\"hljs-number\">1<\/span> | Samsung Galaxy S24         |                  <span class=\"hljs-number\">6<\/span>\n        <span class=\"hljs-number\">1<\/span> |          <span class=\"hljs-number\">6<\/span> | Samsung Galaxy Z Fold <span class=\"hljs-number\">5<\/span>    |                  <span class=\"hljs-number\">6<\/span>\n        <span class=\"hljs-number\">1<\/span> |          <span class=\"hljs-number\">8<\/span> | Samsung Galaxy Tab S9      |                  <span class=\"hljs-number\">6<\/span>\n        <span class=\"hljs-number\">1<\/span> |         <span class=\"hljs-number\">11<\/span> | Samsung Galaxy Buds Pro <span class=\"hljs-number\">2<\/span>  |                  <span class=\"hljs-number\">6<\/span>\n        <span class=\"hljs-number\">1<\/span> |         <span class=\"hljs-number\">13<\/span> | Samsung Galaxy Watch <span class=\"hljs-number\">6<\/span>     |                  <span class=\"hljs-number\">6<\/span>\n        <span class=\"hljs-number\">1<\/span> |         <span class=\"hljs-number\">16<\/span> | Samsung QN900C Neo QLED    |                  <span class=\"hljs-number\">6<\/span>\n        <span class=\"hljs-number\">2<\/span> |          <span class=\"hljs-number\">9<\/span> | Apple iPad Pro <span class=\"hljs-number\">12.9<\/span>        |                  <span class=\"hljs-number\">6<\/span>\n        <span class=\"hljs-number\">2<\/span> |         <span class=\"hljs-number\">10<\/span> | Apple AirPods Pro <span class=\"hljs-number\">3<\/span>        |                  <span class=\"hljs-number\">6<\/span>\n        <span class=\"hljs-number\">2<\/span> |          <span class=\"hljs-number\">2<\/span> | Apple iPhone <span class=\"hljs-number\">15<\/span>            |                  <span class=\"hljs-number\">6<\/span>\n        <span class=\"hljs-number\">2<\/span> |         <span class=\"hljs-number\">12<\/span> | Apple Watch Series <span class=\"hljs-number\">9<\/span>       |                  <span class=\"hljs-number\">6<\/span>\n        <span class=\"hljs-number\">2<\/span> |         <span class=\"hljs-number\">24<\/span> | Apple iMac <span class=\"hljs-number\">24<\/span>\"             |                  6\n        2 |          7 | Apple iPhone 15 Pro Max    |                  6\n        3 |          3 | Huawei Mate 60             |                  1\n        4 |          4 | Xiaomi Mi 14               |                  1\n        5 |          5 | Sony Xperia 1 VI           |                  3\n        5 |         15 | Sony Bravia XR A95K        |                  3\n        5 |         18 | Sony HT-A7000 Soundbar     |                  3\n        6 |         17 | LG G3 OLED                 |                  1\n        7 |         25 | Dell Inspiron 27           |                  4\n        7 |         14 | LG OLED TV C3              |                  4\n        7 |         19 | Bose SoundLink Max         |                  4\n        7 |         20 | Dell XPS 15                |                  4\n        8 |         21 | HP Spectre x360            |                  1\n        9 |         22 | Microsoft Surface Laptop 5 |                  1\n       10 |         23 | Lenovo ThinkPad X1 Carbon  |                  1<\/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>In this query:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><code>PARTITION BY<\/code> divides the rows into partitions by <code>brand_id<\/code>.<\/li>\n\n\n\n<li><code>COUNT(*) OVER (PARTITION BY brand_id)<\/code> returns the number of products within each brand.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id='calculating-the-percentage-of-products-within-each-brand'>Calculating the percentage of products within each brand <a href=\"#calculating-the-percentage-of-products-within-each-brand\" class=\"anchor\" id=\"calculating-the-percentage-of-products-within-each-brand\" title=\"Anchor for Calculating the percentage of products within each brand\">#<\/a><\/h2>\n\n\n\n<p>The following statement uses the <code>COUNT()<\/code> window function to calculate the percentage of products within each brand:<\/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\"><span class=\"hljs-keyword\">SELECT<\/span>\n  product_name,\n  brand_id,\n  COUNT(*) <span class=\"hljs-keyword\">OVER<\/span> (<span class=\"hljs-keyword\">PARTITION<\/span> <span class=\"hljs-keyword\">BY<\/span> brand_id) <span class=\"hljs-keyword\">AS<\/span> products_per_brand,\n  COUNT(*) <span class=\"hljs-keyword\">OVER<\/span> () <span class=\"hljs-keyword\">AS<\/span> total_products,\n  (COUNT(*) <span class=\"hljs-keyword\">OVER<\/span> (<span class=\"hljs-keyword\">PARTITION<\/span> <span class=\"hljs-keyword\">BY<\/span> brand_id) * <span class=\"hljs-number\">100.0<\/span> \/ COUNT(*) <span class=\"hljs-keyword\">OVER<\/span> ())::<span class=\"hljs-type\">DEC<\/span>(<span class=\"hljs-number\">5<\/span>, <span class=\"hljs-number\">2<\/span>) <span class=\"hljs-keyword\">AS<\/span> percentage_per_brand\n<span class=\"hljs-keyword\">FROM<\/span>\n  products;<\/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><a href=\"https:\/\/www.pgtutorial.com\/playground\/?q=U0VMRUNUIHByb2R1Y3RfbmFtZSwgYnJhbmRfaWQsIENPVU5UKCopIE9WRVIgKFBBUlRJVElPTiBCWSBicmFuZF9pZCkgQVMgcHJvZHVjdHNfcGVyX2JyYW5kLCBDT1VOVCgqKSBPVkVSICgpIEFTIHRvdGFsX3Byb2R1Y3RzLCAoQ09VTlQoKikgT1ZFUiAoUEFSVElUSU9OIEJZIGJyYW5kX2lkKSAqIDEwMC4wIC8gQ09VTlQoKikgT1ZFUiAoKSk6OkRFQyg1LCAyKSBBUyBwZXJjZW50YWdlX3Blcl9icmFuZCBGUk9NIHByb2R1Y3RzOw%3D%3D\" target=\"_blank\" rel=\"noreferrer noopener\">Try it<\/a><\/p>\n\n\n\n<p>Output:<\/p>\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\">        product_name        | brand_id | products_per_brand | total_products | percentage_per_brand\n<span class=\"hljs-comment\">----------------------------+----------+--------------------+----------------+----------------------<\/span>\n Samsung Galaxy S24         |        <span class=\"hljs-number\">1<\/span> |                  <span class=\"hljs-number\">6<\/span> |             <span class=\"hljs-number\">25<\/span> |                <span class=\"hljs-number\">24.00<\/span>\n Samsung Galaxy Z Fold <span class=\"hljs-number\">5<\/span>    |        <span class=\"hljs-number\">1<\/span> |                  <span class=\"hljs-number\">6<\/span> |             <span class=\"hljs-number\">25<\/span> |                <span class=\"hljs-number\">24.00<\/span>\n Samsung Galaxy Tab S9      |        <span class=\"hljs-number\">1<\/span> |                  <span class=\"hljs-number\">6<\/span> |             <span class=\"hljs-number\">25<\/span> |                <span class=\"hljs-number\">24.00<\/span>\n Samsung Galaxy Buds Pro <span class=\"hljs-number\">2<\/span>  |        <span class=\"hljs-number\">1<\/span> |                  <span class=\"hljs-number\">6<\/span> |             <span class=\"hljs-number\">25<\/span> |                <span class=\"hljs-number\">24.00<\/span>\n Samsung Galaxy Watch <span class=\"hljs-number\">6<\/span>     |        <span class=\"hljs-number\">1<\/span> |                  <span class=\"hljs-number\">6<\/span> |             <span class=\"hljs-number\">25<\/span> |                <span class=\"hljs-number\">24.00<\/span>\n Samsung QN900C Neo QLED    |        <span class=\"hljs-number\">1<\/span> |                  <span class=\"hljs-number\">6<\/span> |             <span class=\"hljs-number\">25<\/span> |                <span class=\"hljs-number\">24.00<\/span>\n Apple iPad Pro <span class=\"hljs-number\">12.9<\/span>        |        <span class=\"hljs-number\">2<\/span> |                  <span class=\"hljs-number\">6<\/span> |             <span class=\"hljs-number\">25<\/span> |                <span class=\"hljs-number\">24.00<\/span>\n Apple AirPods Pro <span class=\"hljs-number\">3<\/span>        |        <span class=\"hljs-number\">2<\/span> |                  <span class=\"hljs-number\">6<\/span> |             <span class=\"hljs-number\">25<\/span> |                <span class=\"hljs-number\">24.00<\/span>\n Apple iPhone <span class=\"hljs-number\">15<\/span>            |        <span class=\"hljs-number\">2<\/span> |                  <span class=\"hljs-number\">6<\/span> |             <span class=\"hljs-number\">25<\/span> |                <span class=\"hljs-number\">24.00<\/span>\n Apple Watch Series <span class=\"hljs-number\">9<\/span>       |        <span class=\"hljs-number\">2<\/span> |                  <span class=\"hljs-number\">6<\/span> |             <span class=\"hljs-number\">25<\/span> |                <span class=\"hljs-number\">24.00<\/span>\n Apple iMac <span class=\"hljs-number\">24<\/span>\"             |        2 |                  6 |             25 |                24.00\n Apple iPhone 15 Pro Max    |        2 |                  6 |             25 |                24.00\n Huawei Mate 60             |        3 |                  1 |             25 |                 4.00\n Xiaomi Mi 14               |        4 |                  1 |             25 |                 4.00\n Sony Xperia 1 VI           |        5 |                  3 |             25 |                12.00\n Sony Bravia XR A95K        |        5 |                  3 |             25 |                12.00\n Sony HT-A7000 Soundbar     |        5 |                  3 |             25 |                12.00\n LG G3 OLED                 |        6 |                  1 |             25 |                 4.00\n Dell Inspiron 27           |        7 |                  4 |             25 |                16.00\n LG OLED TV C3              |        7 |                  4 |             25 |                16.00\n Bose SoundLink Max         |        7 |                  4 |             25 |                16.00\n Dell XPS 15                |        7 |                  4 |             25 |                16.00\n HP Spectre x360            |        8 |                  1 |             25 |                 4.00\n Microsoft Surface Laptop 5 |        9 |                  1 |             25 |                 4.00\n Lenovo ThinkPad X1 Carbon  |       10 |                  1 |             25 |                 4.00<\/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>In this query:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><code>COUNT(*) OVER (PARTITION BY brand_id)<\/code> returns the number of products per brand.<\/li>\n\n\n\n<li><code>COUNT(*) OVER ()<\/code> returns the total number of products.<\/li>\n\n\n\n<li><code>(COUNT(*) OVER (PARTITION BY brand_id) * 100.0 \/ COUNT(*) OVER ())<\/code> returns the percentage of products within each brand.<\/li>\n<\/ul>\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>COUNT()<\/code> window function to return the number of rows within a partition.<\/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=count-window-function\"\n  height=\"700\"\n  width=\"600\"\n  class=\"iframe\"\n><\/iframe>\n\n<div class=\"helpful-block-content\" 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