{"id":169649,"date":"2023-08-11T15:35:51","date_gmt":"2023-08-11T14:35:51","guid":{"rendered":"https:\/\/datascientest.com\/en\/?p=169649"},"modified":"2024-11-27T14:53:30","modified_gmt":"2024-11-27T13:53:30","slug":"sql-joins-everything-you-need-to-know-about","status":"publish","type":"post","link":"https:\/\/datascientest.com\/en\/sql-joins-everything-you-need-to-know-about","title":{"rendered":"SQL joins: everything you need to know about table associations"},"content":{"rendered":"\t\t<div data-elementor-type=\"wp-post\" data-elementor-id=\"169649\" class=\"elementor elementor-169649\" data-elementor-post-type=\"post\">\n\t\t\t\t\t\t\t<div class=\"elementor-element elementor-element-6745334 e-flex e-con-boxed e-con\" data-id=\"6745334\" data-element_type=\"container\" data-settings=\"{&quot;content_width&quot;:&quot;boxed&quot;}\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-a2889e0 elementor-widget elementor-widget-heading\" data-id=\"a2889e0\" data-element_type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t<style>\/*! elementor - v3.15.0 - 02-08-2023 *\/\n.elementor-heading-title{padding:0;margin:0;line-height:1}.elementor-widget-heading .elementor-heading-title[class*=elementor-size-]>a{color:inherit;font-size:inherit;line-height:inherit}.elementor-widget-heading .elementor-heading-title.elementor-size-small{font-size:15px}.elementor-widget-heading .elementor-heading-title.elementor-size-medium{font-size:19px}.elementor-widget-heading .elementor-heading-title.elementor-size-large{font-size:29px}.elementor-widget-heading .elementor-heading-title.elementor-size-xl{font-size:39px}.elementor-widget-heading .elementor-heading-title.elementor-size-xxl{font-size:59px}<\/style><h2 class=\"elementor-heading-title elementor-size-default\">If you're a regular reader of our blog, you've already heard of SQL or \"Structured Query Language\": a programming language for managing databases, and you know all about the importance of SQL joins. <\/h2>\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-7fd98cd e-flex e-con-boxed e-con\" data-id=\"7fd98cd\" data-element_type=\"container\" data-settings=\"{&quot;content_width&quot;:&quot;boxed&quot;}\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-8b7e47b elementor-widget elementor-widget-heading\" data-id=\"8b7e47b\" data-element_type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t<h3 class=\"elementor-heading-title elementor-size-default\">What is SQL Joins ?<\/h3>\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-223d2ea elementor-widget elementor-widget-text-editor\" data-id=\"223d2ea\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t<style>\/*! elementor - v3.15.0 - 02-08-2023 *\/\n.elementor-widget-text-editor.elementor-drop-cap-view-stacked .elementor-drop-cap{background-color:#69727d;color:#fff}.elementor-widget-text-editor.elementor-drop-cap-view-framed .elementor-drop-cap{color:#69727d;border:3px solid;background-color:transparent}.elementor-widget-text-editor:not(.elementor-drop-cap-view-default) .elementor-drop-cap{margin-top:8px}.elementor-widget-text-editor:not(.elementor-drop-cap-view-default) .elementor-drop-cap-letter{width:1em;height:1em}.elementor-widget-text-editor .elementor-drop-cap{float:left;text-align:center;line-height:1;font-size:50px}.elementor-widget-text-editor .elementor-drop-cap-letter{display:inline-block}<\/style>\t\t\t\t<p>If you missed the article on the\u00a0<a href=\"https:\/\/datascientest.com\/en\/sql-learn-all-about-the-programming-language-for-databases\" target=\"_blank\" rel=\"noopener\">basics of SQL language<\/a>. We&#8217;ll give it to you again here.<\/p><p><span style=\"font-weight: 400;\">At first glance, SQL joins may seem complicated or difficult to apply. DataScientest has put together a quick summary of the main SQL joins, with a simple example to make your life easier! But first of all, what is a join?\u00a0\u00a0<\/span><\/p><p><span style=\"font-weight: 400;\">Joins are used to retrieve data from a database where tables have relationships with each other. They enable you to exploit the tables in a database, link them and obtain efficient results.<\/span><\/p><p><span style=\"font-weight: 400;\">There are several types, and we&#8217;re going to look at the main ones.\u00a0<\/span><\/p><p><span style=\"font-weight: 400;\">\u00a0Throughout this article, we&#8217;ll be relying on two tables:\u00a0<\/span><\/p><ul><li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">the city table shows the cities where the customer corresponding to the customer_id lives,\u00a0<\/span><\/li><li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">the email table gives customer email addresses.<\/span><\/li><\/ul><div>\u00a0<\/div><div><b>City<\/b><\/div>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-f8a5873 elementor-widget__width-initial elementor-widget elementor-widget-image\" data-id=\"f8a5873\" data-element_type=\"widget\" data-widget_type=\"image.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t<style>\/*! elementor - v3.15.0 - 02-08-2023 *\/\n.elementor-widget-image{text-align:center}.elementor-widget-image a{display:inline-block}.elementor-widget-image a img[src$=\".svg\"]{width:48px}.elementor-widget-image img{vertical-align:middle;display:inline-block}<\/style>\t\t\t\t\t\t\t\t\t\t\t\t<img decoding=\"async\" width=\"138\" height=\"111\" src=\"https:\/\/datascientest.com\/en\/files\/2023\/08\/Data1.png\" class=\"attachment-large size-large wp-image-169662\" alt=\"Data1\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-ce31ae6 elementor-widget elementor-widget-text-editor\" data-id=\"ce31ae6\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t<p><strong>Email<\/strong><\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-d3e5b53 elementor-widget__width-initial elementor-widget elementor-widget-image\" data-id=\"d3e5b53\" data-element_type=\"widget\" data-widget_type=\"image.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<img decoding=\"async\" width=\"402\" height=\"109\" src=\"https:\/\/datascientest.com\/en\/files\/2023\/08\/Data2.png\" class=\"attachment-large size-large wp-image-169661\" alt=\"Data2\" srcset=\"https:\/\/datascientest.com\/en\/files\/2023\/08\/Data2.png 402w, https:\/\/datascientest.com\/en\/files\/2023\/08\/Data2-300x81.png 300w\" sizes=\"(max-width: 402px) 100vw, 402px\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-0151bff elementor-align-center button-principal elementor-widget elementor-widget-button\" data-id=\"0151bff\" data-element_type=\"widget\" data-widget_type=\"button.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<div class=\"elementor-button-wrapper\">\n\t\t\t<a class=\"elementor-button elementor-button-link elementor-size-md\" href=\"https:\/\/datascientest.com\/en\/data-analyst-course\">\n\t\t\t\t\t\t<span class=\"elementor-button-content-wrapper\">\n\t\t\t\t\t\t<span class=\"elementor-button-text\">Start learning SQL in minutes<\/span>\n\t\t<\/span>\n\t\t\t\t\t<\/a>\n\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-9fadb78 e-flex e-con-boxed e-con\" data-id=\"9fadb78\" data-element_type=\"container\" data-settings=\"{&quot;content_width&quot;:&quot;boxed&quot;}\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-b55e2c3 elementor-widget elementor-widget-heading\" data-id=\"b55e2c3\" data-element_type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t<h3 class=\"elementor-heading-title elementor-size-default\">1. INNER JOIN<\/h3>\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-c848b9e elementor-widget elementor-widget-text-editor\" data-id=\"c848b9e\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t<p><span style=\"font-weight: 400;\">The internal join or INNER JOIN returns data when the condition is true in both tables.\u00a0\u00a0<\/span><\/p><p><span style=\"font-weight: 400;\">As shown in the diagram, this type of join will concatenate the tuples of 2 tables two by two if a condition is met. This condition can be of any type, as long as it returns <\/span><a href=\"https:\/\/en.wikipedia.org\/wiki\/Boolean_data_type\"><span style=\"font-weight: 400;\">a Boolean<\/span><\/a><span style=\"font-weight: 400;\">. Typically, this condition will be the equality of a common attribute. It is necessary to specify the attributes to be used to perform the join. The ON keyword is used, followed by the desired equality after the tables have been specified in the INNER JOIN.\u00a0<\/span><\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-7a2e269 elementor-widget__width-initial elementor-widget elementor-widget-image\" data-id=\"7a2e269\" data-element_type=\"widget\" data-widget_type=\"image.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<img decoding=\"async\" width=\"300\" height=\"180\" src=\"https:\/\/datascientest.com\/en\/files\/2023\/08\/Inner-join.png\" class=\"attachment-large size-large wp-image-169660\" alt=\"Inner join\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-09cba44 elementor-widget elementor-widget-text-editor\" data-id=\"09cba44\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t<p><span style=\"font-weight: 400;\">This is the query that wastes the most information since it only selects rows in both tables where there is information in both tables.<\/span><\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-589d376 elementor-widget elementor-widget-html\" data-id=\"589d376\" data-element_type=\"widget\" data-widget_type=\"html.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t<script src=\"https:\/\/gist.github.com\/EmilieGreff1\/9c695365de13aad9709b1758a13d7948.js\"><\/script>\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-92a8028 elementor-widget__width-initial elementor-widget elementor-widget-image\" data-id=\"92a8028\" data-element_type=\"widget\" data-widget_type=\"image.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<img decoding=\"async\" width=\"414\" height=\"97\" src=\"https:\/\/datascientest.com\/en\/files\/2023\/08\/Inner-join1.png\" class=\"attachment-large size-large wp-image-169659\" alt=\"Inner join1\" srcset=\"https:\/\/datascientest.com\/en\/files\/2023\/08\/Inner-join1.png 414w, https:\/\/datascientest.com\/en\/files\/2023\/08\/Inner-join1-300x70.png 300w\" sizes=\"(max-width: 414px) 100vw, 414px\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-ac32a26 elementor-widget elementor-widget-text-editor\" data-id=\"ac32a26\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t<p><span style=\"font-weight: 400;\">Here, by performing an INNER JOIN between the two tables, we obtain only the customer IDs present in the email table and in the city table. Customer IDs 4 and 5, which are present in the email table but not in the city table, are not taken into account. The same applies to customer IDs 7 and 8, which are in the city table but not in the email table.<\/span><\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-6c0b1ca elementor-align-center button-principal elementor-widget elementor-widget-button\" data-id=\"6c0b1ca\" data-element_type=\"widget\" data-widget_type=\"button.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<div class=\"elementor-button-wrapper\">\n\t\t\t<a class=\"elementor-button elementor-button-link elementor-size-md\" href=\"https:\/\/datascientest.com\/en\/data-analyst-course\">\n\t\t\t\t\t\t<span class=\"elementor-button-content-wrapper\">\n\t\t\t\t\t\t<span class=\"elementor-button-text\">Learn to use SQL<\/span>\n\t\t<\/span>\n\t\t\t\t\t<\/a>\n\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-eb433fe e-flex e-con-boxed e-con\" data-id=\"eb433fe\" data-element_type=\"container\" data-settings=\"{&quot;content_width&quot;:&quot;boxed&quot;}\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-2fc9fee elementor-widget elementor-widget-heading\" data-id=\"2fc9fee\" data-element_type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t<h3 class=\"elementor-heading-title elementor-size-default\">2. LEFT JOIN\n<\/h3>\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-3568f1e elementor-widget elementor-widget-text-editor\" data-id=\"3568f1e\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t<p><span style=\"font-weight: 400;\">The LEFT JOIN is a join between 2 tables that returns all records from the left-hand table, even if there is no match with the right-hand table. If there is no match, missing values are set to NULL. As with the INNER JOIN, you need to specify the attributes to be used to perform the join: the ON keyword is used, followed by the desired equality after the tables in the LEFT JOIN have been filled in.<\/span><\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-922bcf1 elementor-widget__width-initial elementor-widget elementor-widget-image\" data-id=\"922bcf1\" data-element_type=\"widget\" data-widget_type=\"image.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<img decoding=\"async\" width=\"301\" height=\"180\" src=\"https:\/\/datascientest.com\/en\/files\/2023\/08\/left-join-sql.png\" class=\"attachment-large size-large wp-image-169658\" alt=\"left join sql\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-e6f9568 elementor-widget elementor-widget-text-editor\" data-id=\"e6f9568\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t<p><span style=\"font-weight: 400;\">Here we&#8217;re doing a LEFT JOIN query against the email table, so we&#8217;re displaying all rows when the customer_id is present in the left-hand table, i.e. in the email table.\u00a0\u00a0<\/span><\/p><p><span style=\"font-weight: 400;\">\u00a0Thus the lines corresponding to customer_id 7 and 8 are not present in the query output.<\/span><\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-f59e8f0 elementor-widget elementor-widget-html\" data-id=\"f59e8f0\" data-element_type=\"widget\" data-widget_type=\"html.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t<script src=\"https:\/\/gist.github.com\/EmilieGreff1\/96cd3aa5a2435c4d4622d8cbb550ce76.js\"><\/script>\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-c39906a elementor-widget__width-initial elementor-widget elementor-widget-image\" data-id=\"c39906a\" data-element_type=\"widget\" data-widget_type=\"image.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<img decoding=\"async\" width=\"409\" height=\"119\" src=\"https:\/\/datascientest.com\/en\/files\/2023\/08\/left-join2.png\" class=\"attachment-large size-large wp-image-169657\" alt=\"left join2\" srcset=\"https:\/\/datascientest.com\/en\/files\/2023\/08\/left-join2.png 409w, https:\/\/datascientest.com\/en\/files\/2023\/08\/left-join2-300x87.png 300w\" sizes=\"(max-width: 409px) 100vw, 409px\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-c009c1f elementor-align-center button-principal elementor-widget elementor-widget-button\" data-id=\"c009c1f\" data-element_type=\"widget\" data-widget_type=\"button.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<div class=\"elementor-button-wrapper\">\n\t\t\t<a class=\"elementor-button elementor-button-link elementor-size-md\" href=\"https:\/\/datascientest.com\/en\/data-analyst-course\">\n\t\t\t\t\t\t<span class=\"elementor-button-content-wrapper\">\n\t\t\t\t\t\t<span class=\"elementor-button-text\">Transform your data into insights with SQL<\/span>\n\t\t<\/span>\n\t\t\t\t\t<\/a>\n\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-74593ac e-flex e-con-boxed e-con\" data-id=\"74593ac\" data-element_type=\"container\" data-settings=\"{&quot;content_width&quot;:&quot;boxed&quot;}\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-871c945 elementor-widget elementor-widget-heading\" data-id=\"871c945\" data-element_type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t<h3 class=\"elementor-heading-title elementor-size-default\">3. RIGHT JOIN\n<\/h3>\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-cf76f47 elementor-widget elementor-widget-text-editor\" data-id=\"cf76f47\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t<p><span style=\"font-weight: 400;\">The RIGHT JOIN is a join between 2 tables that returns all records from the right-hand table, even if there is no match with the left-hand table. If there is no match, missing values are set to NULL.\u00a0<\/span><\/p><p><span style=\"font-weight: 400;\">As with INNER JOIN and LEFT JOIN, you need to specify the attributes to be used to perform the join: use the ON keyword followed by the desired equality after entering the tables in the RIGHT JOIN.<\/span><\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-970b01b elementor-widget__width-initial elementor-widget elementor-widget-image\" data-id=\"970b01b\" data-element_type=\"widget\" data-widget_type=\"image.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<img decoding=\"async\" width=\"300\" height=\"180\" src=\"https:\/\/datascientest.com\/en\/files\/2023\/08\/right-join.png\" class=\"attachment-large size-large wp-image-169656\" alt=\"right join\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-6260a87 elementor-widget elementor-widget-text-editor\" data-id=\"6260a87\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t<p><span style=\"font-weight: 400;\">Here we&#8217;re doing a LEFT JOIN query against the email table, so we&#8217;re displaying all rows when the customer_id is present in the left-hand table, i.e. in the email table.\u00a0\u00a0<\/span><\/p><p><span style=\"font-weight: 400;\">\u00a0Thus the lines corresponding to customer_id 7 and 8 are not present in the query output.<\/span><\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-2912abb elementor-widget elementor-widget-html\" data-id=\"2912abb\" data-element_type=\"widget\" data-widget_type=\"html.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t<script src=\"https:\/\/gist.github.com\/EmilieGreff1\/d77f123da8bfafdc10155e2ac7a0611e.js\"><\/script>\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-bdda20c elementor-widget__width-initial elementor-widget elementor-widget-image\" data-id=\"bdda20c\" data-element_type=\"widget\" data-widget_type=\"image.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<img decoding=\"async\" width=\"418\" height=\"108\" src=\"https:\/\/datascientest.com\/en\/files\/2023\/08\/right-join1.png\" class=\"attachment-large size-large wp-image-169655\" alt=\"right join1\" srcset=\"https:\/\/datascientest.com\/en\/files\/2023\/08\/right-join1.png 418w, https:\/\/datascientest.com\/en\/files\/2023\/08\/right-join1-300x78.png 300w\" sizes=\"(max-width: 418px) 100vw, 418px\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-dcc5d1e elementor-align-center button-principal elementor-widget elementor-widget-button\" data-id=\"dcc5d1e\" data-element_type=\"widget\" data-widget_type=\"button.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<div class=\"elementor-button-wrapper\">\n\t\t\t<a class=\"elementor-button elementor-button-link elementor-size-md\" href=\"https:\/\/datascientest.com\/en\/data-analyst-course\">\n\t\t\t\t\t\t<span class=\"elementor-button-content-wrapper\">\n\t\t\t\t\t\t<span class=\"elementor-button-text\">Become an expert on SQL with DataScientest<\/span>\n\t\t<\/span>\n\t\t\t\t\t<\/a>\n\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-f310f10 e-flex e-con-boxed e-con\" data-id=\"f310f10\" data-element_type=\"container\" data-settings=\"{&quot;content_width&quot;:&quot;boxed&quot;}\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-b5c36dd elementor-widget elementor-widget-heading\" data-id=\"b5c36dd\" data-element_type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t<h3 class=\"elementor-heading-title elementor-size-default\">4. FULL JOIN<\/h3>\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-114be8a elementor-widget elementor-widget-text-editor\" data-id=\"114be8a\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t<p><span style=\"font-weight: 400;\">The FULL JOIN is a join between 2 tables that returns all records from both tables, even if there is no match with the other. If there is no match, missing values are set to NULL. This join also requires the ON attribute.\u00a0<\/span><\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-556f85e elementor-widget__width-initial elementor-widget elementor-widget-image\" data-id=\"556f85e\" data-element_type=\"widget\" data-widget_type=\"image.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<img decoding=\"async\" width=\"300\" height=\"180\" src=\"https:\/\/datascientest.com\/en\/files\/2023\/08\/Full-join.png\" class=\"attachment-large size-large wp-image-169665\" alt=\"Full join\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-3c74a8f elementor-widget elementor-widget-text-editor\" data-id=\"3c74a8f\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t<p><span style=\"font-weight: 400;\">Here, it doesn&#8217;t matter if there are no corresponding rows in one of the two tables, all the information from both tables is present. This is the join that keeps as much information as possible.<\/span><\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-a4791d9 elementor-widget elementor-widget-html\" data-id=\"a4791d9\" data-element_type=\"widget\" data-widget_type=\"html.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t<script src=\"https:\/\/gist.github.com\/EmilieGreff1\/d77f123da8bfafdc10155e2ac7a0611e.js\"><\/script>\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-8b8ae82 elementor-widget__width-initial elementor-widget elementor-widget-image\" data-id=\"8b8ae82\" data-element_type=\"widget\" data-widget_type=\"image.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<img decoding=\"async\" width=\"464\" height=\"136\" src=\"https:\/\/datascientest.com\/en\/files\/2023\/08\/FUll-join1.png\" class=\"attachment-large size-large wp-image-169664\" alt=\"FUll join1\" srcset=\"https:\/\/datascientest.com\/en\/files\/2023\/08\/FUll-join1.png 464w, https:\/\/datascientest.com\/en\/files\/2023\/08\/FUll-join1-300x88.png 300w\" sizes=\"(max-width: 464px) 100vw, 464px\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-f4347f2 elementor-align-center button-principal elementor-widget elementor-widget-button\" data-id=\"f4347f2\" data-element_type=\"widget\" data-widget_type=\"button.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<div class=\"elementor-button-wrapper\">\n\t\t\t<a class=\"elementor-button elementor-button-link elementor-size-md\" href=\"https:\/\/datascientest.com\/en\/data-analyst-course\">\n\t\t\t\t\t\t<span class=\"elementor-button-content-wrapper\">\n\t\t\t\t\t\t<span class=\"elementor-button-text\">Start your data analyst journey<\/span>\n\t\t<\/span>\n\t\t\t\t\t<\/a>\n\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-1ec530b e-flex e-con-boxed e-con\" data-id=\"1ec530b\" data-element_type=\"container\" data-settings=\"{&quot;content_width&quot;:&quot;boxed&quot;}\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-99ec787 elementor-widget elementor-widget-heading\" data-id=\"99ec787\" data-element_type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t<h3 class=\"elementor-heading-title elementor-size-default\">5. NATURAL JOIN<\/h3>\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-aa7d625 elementor-widget elementor-widget-text-editor\" data-id=\"aa7d625\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t<p><span style=\"font-weight: 400;\">The NATURAL JOIN is a join between 2 tables that returns records from both tables in a &#8220;natural&#8221; way.\u00a0 There must be at least one column with the same name in both tables. It performs a natural join by returning rows with pairs that match both tables.\u00a0\u00a0<\/span><\/p><p><span style=\"font-weight: 400;\">With NATURAL JOIN, the ON is not specified.<\/span><\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-1e65a7d elementor-widget elementor-widget-html\" data-id=\"1e65a7d\" data-element_type=\"widget\" data-widget_type=\"html.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t<script src=\"https:\/\/gist.github.com\/EmilieGreff1\/2870c540434de8ab3165b74edfce5b40.js\"><\/script>\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-0009c66 elementor-widget__width-initial elementor-widget elementor-widget-image\" data-id=\"0009c66\" data-element_type=\"widget\" data-widget_type=\"image.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<img decoding=\"async\" width=\"414\" height=\"97\" src=\"https:\/\/datascientest.com\/en\/files\/2023\/08\/Natural-join.png\" class=\"attachment-large size-large wp-image-169663\" alt=\"Natural join\" srcset=\"https:\/\/datascientest.com\/en\/files\/2023\/08\/Natural-join.png 414w, https:\/\/datascientest.com\/en\/files\/2023\/08\/Natural-join-300x70.png 300w\" sizes=\"(max-width: 414px) 100vw, 414px\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-f658e4b elementor-widget elementor-widget-text-editor\" data-id=\"f658e4b\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t<p><span style=\"font-weight: 400;\">The output shows that a join has been made between the two tables with &#8220;id_client&#8221;, as this is the only variable present in both tables.\u00a0<\/span><\/p><p><span style=\"font-weight: 400;\">But what&#8217;s the difference between NATURAL JOIN and INNER JOIN?\u00a0\u00a0<\/span><\/p><p><span style=\"font-weight: 400;\">The INNER JOIN avoids the repetition of equal rows, which is not possible with the NATURAL JOIN. The INNER JOIN returns a table based on the data specified in the ON, whereas the NATURAL JOIN returns a table based on a column with the same name and type in both tables.\u00a0\u00a0<\/span><\/p><p><span style=\"font-weight: 400;\">\u00a0The four types of SQL joins to remember are :\u00a0<\/span><\/p><ul><li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">INNER JOIN to retrieve information between two tables when the ON condition is met on both tables,\u00a0<\/span><\/li><li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">LEFT \/ RIGHT JOIN to retrieve information between two tables, keeping all information from one of the two tables,\u00a0<\/span><\/li><li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">FULL JOIN retrieves all information from both tables without loss of information (but may display many NULLs),\u00a0<\/span><\/li><li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">NATURAL JOIN performs a natural join between the two tables, so there&#8217;s no need to specify the ON.\u00a0\u00a0<\/span><\/li><\/ul>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-52535b5 elementor-widget elementor-widget-text-editor\" data-id=\"52535b5\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t<p><span style=\"font-weight: 400;\">Joins are an efficient way of associating several tables. There are several types, and we&#8217;ve already seen the main ones.<\/span><span style=\"font-weight: 400;\">\u00a0<\/span><\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-d7bf362 elementor-align-center button-principal elementor-widget elementor-widget-button\" data-id=\"d7bf362\" data-element_type=\"widget\" data-widget_type=\"button.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<div class=\"elementor-button-wrapper\">\n\t\t\t<a class=\"elementor-button elementor-button-link elementor-size-md\" href=\"https:\/\/datascientest.com\/en\/data-analyst-course\">\n\t\t\t\t\t\t<span class=\"elementor-button-content-wrapper\">\n\t\t\t\t\t\t<span class=\"elementor-button-text\">Discover the Data Analyst course<\/span>\n\t\t<\/span>\n\t\t\t\t\t<\/a>\n\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t\t\t<\/div>\n\t\t","protected":false},"excerpt":{"rendered":"<p>If you&#8217;re a regular reader of our blog, you&#8217;ve already heard of SQL or &#8220;Structured Query Language&#8221;: a programming language for managing databases, and you know all about the importance of SQL joins. What is SQL Joins ? If you missed the article on the\u00a0basics of SQL language. We&#8217;ll give it to you again here. [&hellip;]<\/p>\n","protected":false},"author":45,"featured_media":169651,"comment_status":"open","ping_status":"open","sticky":false,"template":"elementor_theme","format":"standard","meta":{"content-type":"","inline_featured_image":false},"categories":[2425],"tags":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v21.7 (Yoast SEO v21.7) - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>SQL joins: everything you need to know about table associations<\/title>\n<meta name=\"description\" content=\"If you&#039;re a regular reader of our blog, you&#039;ve already heard of SQL or &quot;Structured Query Language&quot;: a programming language for managing databases, and you know all about the importance of SQL joins.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/datascientest.com\/en\/sql-joins-everything-you-need-to-know-about\" 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