{"id":1489,"date":"2023-05-01T09:37:53","date_gmt":"2023-05-01T09:37:53","guid":{"rendered":"http:\/\/localhost\/codeera\/?p=1489"},"modified":"2023-05-02T09:33:10","modified_gmt":"2023-05-02T09:33:10","slug":"10-essential-sql-queries-every-developer-should-know","status":"publish","type":"post","link":"http:\/\/localhost\/codeera\/2023\/05\/01\/10-essential-sql-queries-every-developer-should-know\/","title":{"rendered":"10 Essential SQL Queries Every Developer Should Know"},"content":{"rendered":"\t\t<div data-elementor-type=\"wp-post\" data-elementor-id=\"1489\" class=\"elementor elementor-1489\">\n\t\t\t\t\t\t\t\t\t<section class=\"elementor-section elementor-top-section elementor-element elementor-element-2c07dccd elementor-section-boxed elementor-section-height-default elementor-section-height-default\" data-id=\"2c07dccd\" data-element_type=\"section\">\n\t\t\t\t\t\t<div class=\"elementor-container elementor-column-gap-default\">\n\t\t\t\t\t<div class=\"elementor-column elementor-col-100 elementor-top-column elementor-element elementor-element-36b3a53b\" data-id=\"36b3a53b\" data-element_type=\"column\">\n\t\t\t<div class=\"elementor-widget-wrap elementor-element-populated\">\n\t\t\t\t\t\t\t\t<div class=\"elementor-element elementor-element-22e1be39 elementor-widget elementor-widget-text-editor\" data-id=\"22e1be39\" 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 - v3.11.1 - 15-02-2023 *\/\n.elementor-widget-text-editor.elementor-drop-cap-view-stacked .elementor-drop-cap{background-color:#818a91;color:#fff}.elementor-widget-text-editor.elementor-drop-cap-view-framed .elementor-drop-cap{color:#818a91;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><!-- wp:list {\"ordered\":true} --><\/p>\n<ol>\n<li style=\"list-style-type: none;\">\n<ol><!-- wp:list-item --><\/ol>\n<\/li>\n<\/ol>\n<h5><b>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a01. SELECT:<\/b><\/h5>\n<p>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0The SELECT statement is used to retrieve data from one or more tables in a database. It is the most basic and fundamental\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0SQL query. The SELECT statement can be used to retrieve all columns from a table, or only specific columns using the\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0SELECT column1, column2 syntax. The WHERE clause can also be added to the SELECT statement to filter records based on\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0a condition.<\/p>\n<p><!-- \/wp:list-item --><\/p>\n<p><!-- \/wp:list --><!-- wp:paragraph --><\/p>\n<p>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0Example:<\/p>\n<p><!-- \/wp:paragraph --><!-- wp:preformatted --><\/p>\n<pre class=\"wp-block-preformatted\"><code><b>     SELECT * FROM employees;<\/b>\n<\/code><\/pre>\n<p><!-- \/wp:preformatted --><!-- wp:paragraph --><\/p>\n<p>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0This query retrieves all columns from the &#8220;employees&#8221; table.<\/p>\n<p>\u00a0<\/p>\n<p><!-- \/wp:paragraph --><!-- wp:list {\"ordered\":true,\"start\":2} --><\/p>\n<ol start=\"2\">\n<li style=\"list-style-type: none;\">\n<ol start=\"2\"><!-- wp:list-item --><\/ol>\n<\/li>\n<\/ol>\n<h5><b>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a02. WHERE:<\/b><\/h5>\n<p>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0The WHERE clause is used to filter records based on a condition. It is used with the SELECT, UPDATE, and DELETE\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0statements. The WHERE clause specifies a condition that must be met for the query to return a row. Multiple conditions\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0can be combined using AND and OR operators.<\/p>\n<p><!-- \/wp:list-item --><\/p>\n<p><!-- \/wp:list --><!-- wp:paragraph --><\/p>\n<p>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 Example:<\/p>\n<p><!-- \/wp:paragraph --><!-- wp:preformatted --><\/p>\n<pre class=\"wp-block-preformatted\"><code>     <b>SELECT * FROM employees WHERE department = 'sales';<\/b>\n<\/code><\/pre>\n<p><!-- \/wp:preformatted --><!-- wp:paragraph --><\/p>\n<p>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 This query retrieves all columns from the &#8220;employees&#8221; table where the department is &#8220;sales&#8221;.<\/p>\n<p><!-- \/wp:paragraph --><!-- wp:list {\"ordered\":true,\"start\":3} --><\/p>\n<ol start=\"3\">\n<li style=\"list-style-type: none;\">\n<ol start=\"3\"><!-- wp:list-item --><\/ol>\n<\/li>\n<\/ol>\n<h5><strong>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a03. GROUP BY:<\/strong><\/h5>\n<p>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 The GROUP BY clause is used to group records based on one or more columns. It is used with the SELECT statement to\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0retrieve aggregate data, such as the sum or average of a column, for each group. The GROUP BY clause should always be\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 used with an aggregate function, such as SUM or AVG.<\/p>\n<p><!-- \/wp:list-item --><\/p>\n<p><!-- \/wp:list --><!-- wp:paragraph --><\/p>\n<p>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 Example:<\/p>\n<p><!-- \/wp:paragraph --><!-- wp:preformatted --><\/p>\n<pre class=\"wp-block-preformatted\"><code><b>     SELECT department, AVG(salary) FROM employees GROUP BY department;<\/b>\n<\/code><\/pre>\n<p><!-- \/wp:preformatted --><!-- wp:paragraph --><\/p>\n<p>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 This query retrieves the average salary for each department in the &#8220;employees&#8221; table.<\/p>\n<p><!-- \/wp:paragraph --><!-- wp:list {\"ordered\":true,\"start\":4} --><\/p>\n<ol start=\"4\">\n<li style=\"list-style-type: none;\">\n<ol start=\"4\"><!-- wp:list-item --><\/ol>\n<\/li>\n<\/ol>\n<h5>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a04. JOIN:<\/h5>\n<p>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0The JOIN clause is used to combine records from two or more tables based on a common column. There are several types of\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 JOINs, including INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL OUTER JOIN. The JOIN clause specifies the columns from each\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 table that are used to match records.<\/p>\n<p><!-- \/wp:list-item --><\/p>\n<p><!-- \/wp:list --><!-- wp:paragraph --><\/p>\n<p>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 Example:<\/p>\n<p><!-- \/wp:paragraph --><!-- wp:preformatted --><\/p>\n<pre class=\"wp-block-preformatted\"><code><b>     SELECT employees.name, departments.department_name \n     FROM employees \n     INNER JOIN departments ON employees.department_id = departments.department_id;<\/b>\n<\/code><\/pre>\n<p><!-- \/wp:preformatted --><!-- wp:paragraph --><\/p>\n<p>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 This query retrieves the name of each employee along with the name of their department. The INNER JOIN ensures that only\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 employees with a department are included in the result set.<\/p>\n<p><!-- \/wp:paragraph --><!-- wp:list {\"ordered\":true,\"start\":5} --><\/p>\n<ol start=\"5\">\n<li style=\"list-style-type: none;\">\n<ol start=\"5\"><!-- wp:list-item --><\/ol>\n<\/li>\n<\/ol>\n<h5>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a05. ORDER BY:<\/h5>\n<p>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 The ORDER BY clause is used to sort records based on one or more columns. It is used with the SELECT statement. The\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 ORDER BY clause can be used to sort records in ascending or descending order.<\/p>\n<p><!-- \/wp:list-item --><\/p>\n<p><!-- \/wp:list --><!-- wp:paragraph --><\/p>\n<p>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 Example:<\/p>\n<p><!-- \/wp:paragraph --><!-- wp:preformatted --><\/p>\n<pre class=\"wp-block-preformatted\"><code>     <b>SELECT name, salary FROM employees ORDER BY salary DESC;<\/b>\n<\/code><\/pre>\n<p><!-- \/wp:preformatted --><!-- wp:paragraph --><\/p>\n<p>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0This query retrieves the name and salary of each employee in the &#8220;employees&#8221; table, sorted by salary in descending order.<\/p>\n<p><!-- \/wp:paragraph --><!-- wp:list {\"ordered\":true,\"start\":6} --><\/p>\n<ol start=\"6\">\n<li style=\"list-style-type: none;\">\n<ol start=\"6\"><!-- wp:list-item --><\/ol>\n<\/li>\n<\/ol>\n<h5>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 6. INSERT:<\/h5>\n<p>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0The INSERT statement is used to add new records to a table. It is used with the VALUES keyword to specify the values to be\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 inserted into each column.<\/p>\n<p><!-- \/wp:list-item --><\/p>\n<p><!-- \/wp:list --><!-- wp:paragraph --><\/p>\n<p>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0Example:<\/p>\n<p><!-- \/wp:paragraph --><!-- wp:preformatted --><\/p>\n<pre class=\"wp-block-preformatted\"><code>    <b>INSERT INTO employees (name, department, salary) VALUES ('John Smith', 'IT', 50000);<\/b>\n<\/code><\/pre>\n<p><!-- \/wp:preformatted --><!-- wp:paragraph --><\/p>\n<p>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0This query inserts a new record into the &#8220;employees&#8221; table with the name &#8220;John Smith&#8221;, department &#8220;IT&#8221;, and salary &#8220;50000&#8221;.<\/p>\n<p><!-- \/wp:paragraph --><!-- wp:list {\"ordered\":true,\"start\":7} --><\/p>\n<ol start=\"7\">\n<li style=\"list-style-type: none;\">\n<ol start=\"7\"><!-- wp:list-item --><\/ol>\n<\/li>\n<\/ol>\n<h5>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 7. UPDATE:<\/h5>\n<p>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 The UPDATE statement is used to modify existing records in a table. It is used with the SET keyword to specify the new values\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 for each column, and the WHERE clause to specify which records to update.<\/p>\n<p><!-- \/wp:list-item --><\/p>\n<p><!-- \/wp:list --><!-- wp:paragraph --><\/p>\n<p>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 Example:<\/p>\n<p><!-- \/wp:paragraph --><!-- wp:preformatted --><\/p>\n<pre class=\"wp-block-preformatted\"><code>     <b>UPDATE employees SET salary = 55000 WHERE name = 'John Smith';<\/b>\n<\/code><\/pre>\n<p><!-- \/wp:preformatted --><!-- wp:paragraph --><\/p>\n<p>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0This query updates the salary for the employee named &#8220;John Smith&#8221; in the &#8220;employees&#8221; table to &#8220;55000&#8221;.<\/p>\n<p><!-- \/wp:paragraph --><!-- wp:list {\"ordered\":true,\"start\":8} --><\/p>\n<ol start=\"8\">\n<li style=\"list-style-type: none;\">\n<ol start=\"8\"><!-- wp:list-item --><\/ol>\n<\/li>\n<\/ol>\n<h5>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 8. DELETE:<\/h5>\n<p>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0The DELETE statement is used to remove records from a table. It is used with the WHERE clause to specify which records to\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0delete.<\/p>\n<p><!-- \/wp:list-item --><\/p>\n<p><!-- \/wp:list --><!-- wp:paragraph --><\/p>\n<p>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0Example:<\/p>\n<p><!-- \/wp:paragraph --><!-- wp:preformatted --><\/p>\n<pre class=\"wp-block-preformatted\"><code>    <b>DELETE FROM employees WHERE name = 'John Smith';\n<\/b><\/code><\/pre>\n<p><!-- \/wp:preformatted --><!-- wp:paragraph --><\/p>\n<p>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0This query deletes the record for the employee named &#8220;John Smith&#8221; from employees table.<\/p>\n<h5>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 9. DISTINCT:<\/h5>\n<p>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 The DISTINCT keyword is used to remove duplicates from a result set. This query is used to retrieve only unique values from\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0a column or set of columns.<\/p>\n<p>\u00a0<\/p>\n<h5>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 10. LIMIT:<\/h5>\n<p>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 The LIMIT clause is used to limit the number of records returned by a query. This query is used to retrieve a specified\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0number of records from a table.<\/p>\n<p><!-- \/wp:paragraph --><!-- wp:paragraph --><\/p>\n<p><!-- \/wp:paragraph --><\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t\t\t\t<\/div>\n\t\t","protected":false},"excerpt":{"rendered":"<p>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0Example: SELECT * FROM employees; \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0This query retrieves all columns from the &#8220;employees&#8221; table. \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 Example: SELECT * FROM employees WHERE department = &#8216;sales&#8217;; \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 &hellip;<\/p>\n<p class=\"read-more\"> <a class=\"\" href=\"http:\/\/localhost\/codeera\/2023\/05\/01\/10-essential-sql-queries-every-developer-should-know\/\"> <span class=\"screen-reader-text\">10 Essential SQL Queries Every Developer Should Know<\/span> Read More &raquo;<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"site-sidebar-layout":"default","site-content-layout":"default","ast-global-header-display":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","footnotes":""},"categories":[1],"tags":[],"_links":{"self":[{"href":"http:\/\/localhost\/codeera\/wp-json\/wp\/v2\/posts\/1489"}],"collection":[{"href":"http:\/\/localhost\/codeera\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/localhost\/codeera\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/localhost\/codeera\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/localhost\/codeera\/wp-json\/wp\/v2\/comments?post=1489"}],"version-history":[{"count":19,"href":"http:\/\/localhost\/codeera\/wp-json\/wp\/v2\/posts\/1489\/revisions"}],"predecessor-version":[{"id":1560,"href":"http:\/\/localhost\/codeera\/wp-json\/wp\/v2\/posts\/1489\/revisions\/1560"}],"wp:attachment":[{"href":"http:\/\/localhost\/codeera\/wp-json\/wp\/v2\/media?parent=1489"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/localhost\/codeera\/wp-json\/wp\/v2\/categories?post=1489"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/localhost\/codeera\/wp-json\/wp\/v2\/tags?post=1489"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}