{"id":4001,"date":"2025-06-07T09:30:53","date_gmt":"2025-06-07T09:30:53","guid":{"rendered":"https:\/\/w3buddy.com\/?post_type=cposts&#038;p=4001"},"modified":"2025-06-07T09:30:54","modified_gmt":"2025-06-07T09:30:54","slug":"sql-null-handling","status":"publish","type":"cposts","link":"https:\/\/w3buddy.com\/blog\/notes\/sql\/sql-null-handling\/","title":{"rendered":"SQL NULL Handling"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\">In SQL, <code>NULL<\/code> represents a <strong>missing, undefined, or unknown value<\/strong> \u2014 it\u2019s <em>not<\/em> the same as an empty string or zero. Understanding how to work with <code>NULL<\/code> is crucial to writing accurate queries.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\ud83d\udd39 <strong>What is NULL?<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><code>NULL<\/code> means <em>no value<\/em> or <em>unknown<\/em>.<\/li>\n\n\n\n<li>It\u2019s a placeholder \u2014 not equal to anything, even another <code>NULL<\/code>.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">\ud83d\udd39 <strong>Checking for NULL<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Use <code>IS NULL<\/code> and <code>IS NOT NULL<\/code> \u2014 not <code>=<\/code> or <code>!=<\/code>.<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code><code>-- Find rows where email is missing\nSELECT * FROM users WHERE email IS NULL;\n\n-- Find rows where email is present\nSELECT * FROM users WHERE email IS NOT NULL;<\/code><\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\ud83d\udd39 <strong>NULL and Comparison Operators<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-code\"><code><code>-- This will NOT return any results\nSELECT * FROM users WHERE email = NULL;  -- \u274c Wrong\n\n-- Use IS NULL instead\nSELECT * FROM users WHERE email IS NULL;  -- \u2705 Correct<\/code><\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\ud83d\udd39 <strong>Handling NULL in Results<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Use functions to deal with NULL values:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code><code>-- Replace NULL with a default value\nSELECT COALESCE(phone, 'Not Provided') AS phone_display FROM users;\n\n-- MySQL alternative: IFNULL(phone, 'N\/A')\n-- SQL Server alternative: ISNULL(phone, 'N\/A')<\/code><\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\ud83d\udd39 <strong>NULL in Aggregates<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Aggregate functions like <code>COUNT<\/code>, <code>AVG<\/code>, <code>SUM<\/code> ignore NULLs (except <code>COUNT(*)<\/code> includes them).<\/li>\n<\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code><code>SELECT COUNT(email) FROM users;         -- Ignores NULLs\nSELECT COUNT(*) FROM users;             -- Counts all rows<\/code><\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\ud83e\udde0 <strong>Quick Recap<\/strong><\/p>\n\n\n\n<figure class=\"wp-block-table has-small-font-size\"><table><thead><tr><th>Key Point<\/th><th>Description<\/th><\/tr><\/thead><tbody><tr><td>NULL Meaning<\/td><td>Unknown or missing value<\/td><\/tr><tr><td>Check NULL<\/td><td>Use <code>IS NULL<\/code> \/ <code>IS NOT NULL<\/code><\/td><\/tr><tr><td>Comparisons<\/td><td><code>NULL = NULL<\/code> is false! Use IS NULL<\/td><\/tr><tr><td>Replace NULL<\/td><td>Use <code>COALESCE<\/code>, <code>ISNULL<\/code>, or <code>IFNULL<\/code><\/td><\/tr><tr><td>Aggregates<\/td><td>Most functions ignore NULLs<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">\ud83d\udca1 Always be mindful of NULLs \u2014 they can silently break logic if not handled properly.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>In SQL, NULL represents a missing, undefined, or unknown value \u2014 it\u2019s not the same as an empty string or zero. Understanding how to work with NULL is crucial to writing accurate queries. \ud83d\udd39 What is NULL? \ud83d\udd39 Checking for NULL Use IS NULL and IS NOT NULL \u2014 not = or !=. \ud83d\udd39 NULL [&hellip;]<\/p>\n","protected":false},"template":"","meta":{"googlesitekit_rrm_CAowu461DA:productID":""},"categories":[952,979],"class_list":["post-4001","cposts","type-cposts","status-publish","hentry","category-notes","category-sql"],"_links":{"self":[{"href":"https:\/\/w3buddy.com\/blog\/wp-json\/wp\/v2\/cposts\/4001","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/w3buddy.com\/blog\/wp-json\/wp\/v2\/cposts"}],"about":[{"href":"https:\/\/w3buddy.com\/blog\/wp-json\/wp\/v2\/types\/cposts"}],"wp:attachment":[{"href":"https:\/\/w3buddy.com\/blog\/wp-json\/wp\/v2\/media?parent=4001"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/w3buddy.com\/blog\/wp-json\/wp\/v2\/categories?post=4001"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}