{"id":862,"date":"2019-06-26T23:12:47","date_gmt":"2019-06-26T14:12:47","guid":{"rendered":"https:\/\/itips.krsw.biz\/?p=862"},"modified":"2019-06-26T23:12:47","modified_gmt":"2019-06-26T14:12:47","slug":"mysql-blank-decode","status":"publish","type":"post","link":"https:\/\/itips.krsw.biz\/en\/mysql-blank-decode\/","title":{"rendered":"Replace blank column in MySQL"},"content":{"rendered":"<p><img decoding=\"async\" src=\"https:\/\/itips.krsw.biz\/wp-content\/uploads\/2019\/01\/database_1548164993-272x300.png\" alt=\"Replace blank column in MySQL\" width=\"272\" height=\"300\" class=\"alignnone size-medium wp-image-280\" srcset=\"https:\/\/itips.krsw.biz\/wp-content\/uploads\/2019\/01\/database_1548164993-272x300.png 272w, https:\/\/itips.krsw.biz\/wp-content\/uploads\/2019\/01\/database_1548164993-580x640.png 580w, https:\/\/itips.krsw.biz\/wp-content\/uploads\/2019\/01\/database_1548164993-724x800.png 724w, https:\/\/itips.krsw.biz\/wp-content\/uploads\/2019\/01\/database_1548164993-290x320.png 290w, https:\/\/itips.krsw.biz\/wp-content\/uploads\/2019\/01\/database_1548164993-768x848.png 768w, https:\/\/itips.krsw.biz\/wp-content\/uploads\/2019\/01\/database_1548164993-927x1024.png 927w, https:\/\/itips.krsw.biz\/wp-content\/uploads\/2019\/01\/database_1548164993.png 1159w\" sizes=\"(max-width: 272px) 100vw, 272px\" \/><\/p>\n<p>Replace blank column in MySQL.<\/p>\n<p>Sometimes you want to run some special process when a specific column has no value in database.<br \/>\nBut in case of MySQL, it is not easy to find <strong>no value<\/strong>.<\/p>\n<p><\/br><\/p>\n<h2>There are 2 types of &quot;No value&quot;<\/h2>\n<p>You may think that &quot;No value&quot; is &quot;No value&quot;.<br \/>\nBut there are 2 types of &quot;No value&quot; in database.<\/p>\n<ul>\n<li>blank<\/li>\n<li>NULL<\/li>\n<\/ul>\n<p><\/br><\/p>\n<h3>blank<\/h3>\n<p>Blank is a state like <code>&quot;&quot;<\/code>.<br \/>\nIt is like a box that contains nothing.<\/p>\n<p><\/br><\/p>\n<h3>NULL<\/h3>\n<p>NULL is <code>NULL<\/code> in database.<br \/>\nIt is like <strong>not prepared<\/strong> state.<\/p>\n<p><\/br><\/p>\n<h2>blank is not same as NULL<\/h2>\n<p>According to the SQL below, blank is not same as NULL.<\/p>\n<p>SQL<\/p>\n<pre class=\"prettyprint lang-sql\">\nselect \n  (CASE WHEN &#34;&#34;=NULL THEN 1\n   ELSE  0 END) as null_is_blank\nfrom dual;\n<\/pre>\n<p>Result<\/p>\n<pre class=\"prettyprint\">\nnull_is_blank\n0\n<\/pre>\n<p>But in case of <code>!=&#039;&#039;<\/code>, blank seems same as NULL.<\/p>\n<blockquote>\n<p>SELECT * FROM tbl_name WHERE str != '';<br \/>\n\u2192 blank and NULL are excluded.<br \/>\n<a href=\"http:\/\/d.hatena.ne.jp\/mikenews\/20130408\/1365391870\">NULL and blank in MySQL<\/a><\/p>\n<\/blockquote>\n<p>So in order to deal with &quot;No value&quot;, we should replase NULL or blank.<\/p>\n<p><\/br><\/p>\n<h2>Replace blank<\/h2>\n<p>Then we try to replace blank.<br \/>\nBut still we have a problem.<br \/>\nIn Oracle, we can use <code>DECODE<\/code> to replace some specific value with new one.<br \/>\nIn MySQL, we don't have <code>DECODE<\/code>.<br \/>\nSo it takes 2 steps.<\/p>\n<ul>\n<li>Replace blank with NULL by <code>nullif<\/code><\/li>\n<li>Then replace NULL with specific value by <code>ifnull<\/code><\/li>\n<\/ul>\n<pre class=\"prettyprint lang-sql\">\nifnull(nullif(target column,&#39;&#39;),&#39;specific value&#39;)\n<\/pre>\n<p><\/br><\/p>\n<h2>Finally<\/h2>\n<ul>\n<li>There are different types of &quot;No value&quot;. Blank and NULL.<\/li>\n<li>MySQL doesn't have DECODE function.<\/li>\n<li>In order to replace blank, you should replace it with NULL and replace NULL with specific value.<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>Replace blank column in MySQL. Sometimes you want to run some special process when a specific column &#8230; <\/p>\n","protected":false},"author":1,"featured_media":280,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_locale":"en_US","_original_post":"298","footnotes":""},"categories":[14,2],"tags":[69],"class_list":["post-862","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-db","category-dev","tag-mysql","en-US"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.4 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Replace blank column in MySQL - ITips\u30b7\u30b9\u30c6\u30e0\u30bd\u30ea\u30e5\u30fc\u30b7\u30e7\u30f3\u30ba<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/itips.krsw.biz\/en\/mysql-blank-decode\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Replace blank column in MySQL - ITips\u30b7\u30b9\u30c6\u30e0\u30bd\u30ea\u30e5\u30fc\u30b7\u30e7\u30f3\u30ba\" \/>\n<meta property=\"og:description\" content=\"Replace blank column in MySQL. 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