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{"id":5005,"date":"2022-10-26T05:57:29","date_gmt":"2022-10-26T05:57:29","guid":{"rendered":"https:\/\/www.wikitechy.com\/interview-questions\/?p=5005"},"modified":"2022-10-26T05:58:33","modified_gmt":"2022-10-26T05:58:33","slug":"what-is-join-in-dbms-and-what-are-its-types","status":"publish","type":"post","link":"https:\/\/www.wikitechy.com\/interview-questions\/dbms\/what-is-join-in-dbms-and-what-are-its-types\/","title":{"rendered":"What is Join in DBMS and what are its types ?"},"content":{"rendered":"<ul>\n<li>DBMS join is a binary operation that allows combining join products and selecting in one single statement.<\/li>\n<li>If data needs to be retrieved from two or more tables, we can use joins to retrieve data.<\/li>\n<li>Tables in DBMS are associated with the primary key and foreign keys.<\/li>\n<\/ul>\n<p><img fetchpriority=\"high\" decoding=\"async\" class=\"alignnone size-full wp-image-5010 aligncenter\" src=\"https:\/\/www.wikitechy.com\/interview-questions\/wp-content\/uploads\/2022\/10\/what-are-dbms-join-operations.jpg\" alt=\"\" width=\"580\" height=\"262\" srcset=\"https:\/\/www.wikitechy.com\/interview-questions\/wp-content\/uploads\/2022\/10\/what-are-dbms-join-operations.jpg 580w, https:\/\/www.wikitechy.com\/interview-questions\/wp-content\/uploads\/2022\/10\/what-are-dbms-join-operations-300x136.jpg 300w, https:\/\/www.wikitechy.com\/interview-questions\/wp-content\/uploads\/2022\/10\/what-are-dbms-join-operations-390x176.jpg 390w\" sizes=\"(max-width: 580px) 100vw, 580px\" \/><\/p>\n<h3 id=\"types-of-joins\"><strong>Types of Joins<\/strong><\/h3>\n<p><strong>Inner Joins:<\/strong> Theta, Natural, EQUI<\/p>\n<p><strong>Outer Join:<\/strong> Left, Right, Full<\/p>\n<h3 id=\"inner-joins\"><strong>Inner Joins<\/strong><\/h3>\n<ul>\n<li>We can use an inner join to return rows from both tables based on a satisfying condition.<\/li>\n<li>It is the default join type and is the most widely used join operation.<\/li>\n<li>Inner join can classify into three subtypes<\/li>\n<\/ul>\n<h3 id=\"theta-join\"><strong>Theta Join<\/strong><\/h3>\n<ul>\n<li>It is represented by the symbol \u03b8 which allows us to join two tables based on condition.<\/li>\n<li>This join works for all comparison operators<\/li>\n<li>This join is also called Theta Join.<\/li>\n<\/ul>\n<h3 id=\"syntax\"><strong>Syntax<\/strong><\/h3>\n<div class=\"code-embed-wrapper\"> <div class=\"code-embed-infos\"> <\/div> <pre class=\"language-sql code-embed-pre line-numbers\"  data-start=\"1\" data-line-offset=\"0\"><code class=\"language-sql code-embed-code\">A \u22c8\u03b8 B<\/code><\/pre> <\/div>\n<ul>\n<li>Theta join can use any conditions in the selection criteria.<\/li>\n<\/ul>\n<h2 id=\"natural-join\"><strong>Natural Join<\/strong><\/h2>\n<ul>\n<li>This join does not use any comparison operators.<\/li>\n<li>Attributes should have the same name and domain in this join.<\/li>\n<li>In this join, two relations should have at least one common attribute between relations.<\/li>\n<li>It performs selection forming equality on those attributes which appear in both relations by eliminating the duplicate attributes.<\/li>\n<\/ul>\n<h2 id=\"equi-join\"><strong>EQUI join<\/strong><\/h2>\n<ul>\n<li>When Theta join uses an equivalence condition, the EQUI join can be used.<\/li>\n<li>This join is the most difficult join to be done on an RDBMS because RDBMS have fundamental performance problems.<\/li>\n<\/ul>\n<h2 id=\"outer-join\"><strong>Outer Join<\/strong><\/h2>\n<ul>\n<li>This join returns all the attributes of both tables depending on certain conditions.<\/li>\n<li>If there are no attributes present for any one of the tables, it returns NULL irrespective of a row of the table attribute.<\/li>\n<li>Outer Join is further classified as:\n<ul>\n<li>Left Outer Join<\/li>\n<li>Right Outer Join<\/li>\n<li>Full Outer Join<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<h3 id=\"left-outer-join\"><strong>Left Outer Join<\/strong><\/h3>\n<ul>\n<li>If a left outer join is performed on two tables, it returns all the rows of the left table, even if there is no matching row for it in the right table.<\/li>\n<\/ul>\n<h3 id=\"syntax-2\"><strong>Syntax<\/strong><\/h3>\n<div class=\"code-embed-wrapper\"> <div class=\"code-embed-infos\"> <\/div> <pre class=\"language-sql code-embed-pre line-numbers\"  data-start=\"1\" data-line-offset=\"0\"><code class=\"language-sql code-embed-code\">A\u00a0Left Outer Join\u00a0B<\/code><\/pre> <\/div>\n<h3 id=\"right-outer-join\"><strong>Right Outer Join<\/strong><\/h3>\n<ul>\n<li>It returns all the rows of the second table even if there is no matching row in the first table, performing Right Outer Join.<\/li>\n<\/ul>\n<h3 id=\"syntax-3\"><strong>Syntax<\/strong><\/h3>\n<div class=\"code-embed-wrapper\"> <div class=\"code-embed-infos\"> <\/div> <pre class=\"language-sql code-embed-pre line-numbers\"  data-start=\"1\" data-line-offset=\"0\"><code class=\"language-sql code-embed-code\">A Right Outer Join\u00a0B<\/code><\/pre> <\/div>\n<h3 id=\"full-outer-join\"><strong>Full Outer Join<\/strong><\/h3>\n<ul>\n<li>It returns all the rows of the first and second Table.<\/li>\n<\/ul>\n<h3 id=\"syntax-4\"><strong>Syntax<\/strong><\/h3>\n<div class=\"code-embed-wrapper\"> <div class=\"code-embed-infos\"> <\/div> <pre class=\"language-sql code-embed-pre line-numbers\"  data-start=\"1\" data-line-offset=\"0\"><code class=\"language-sql code-embed-code\">A\u00a0Full Outer Join\u00a0B<\/code><\/pre> <\/div>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>DBMS join is a binary operation that allows combining join products and selecting in one single statement. If data needs to be retrieved from two or more tables, we can use joins to retrieve data. Tables in DBMS are associated with the primary key and foreign keys. Types of Joins Inner Joins: Theta, Natural, EQUI [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"passster_activate_protection":false,"passster_protect_child_pages":"","passster_protection_type":"password","passster_password":"","passster_activate_overwrite_defaults":"","passster_headline":"","passster_instruction":"","passster_placeholder":"","passster_button":"","passster_id":"","passster_activate_misc_settings":"","passster_redirect_url":"","passster_hide":"no","passster_area_shortcode":"","gtb_hide_title":false,"gtb_wrap_title":false,"gtb_class_title":"","gtb_remove_headerfooter":false,"footnotes":""},"categories":[7157],"tags":[18944,18934,18936,18935,18941,18942,17431,18938,18943,17432,18940,17428,18939,18933,18937],"class_list":["post-5005","post","type-post","status-publish","format-standard","hentry","category-dbms","tag-cross-join-in-dbms","tag-dbms-join-operation","tag-dbms-joins","tag-dbms-sql-joins","tag-inner-join-in-dbms","tag-join-in-dbms-with-examples","tag-join-operation-in-dbms","tag-join-operation-in-dbms-with-example","tag-join-operation-in-relational-algebra","tag-joins-in-dbms","tag-natural-join-operation-in-dbms","tag-sql-joins","tag-types-of-join-operation-in-dbms","tag-what-is-join-in-dbms-and-what-are-its-types","tag-what-is-join-operation-in-relational-algebra"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v22.6 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>What is Join in DBMS and what are its types ? 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