{"id":12261,"date":"2023-11-11T06:12:16","date_gmt":"2023-11-11T13:12:16","guid":{"rendered":"https:\/\/www.mysqltutorial.org\/?page_id=12261"},"modified":"2023-11-12T21:44:36","modified_gmt":"2023-11-13T04:44:36","slug":"mysql-myisam","status":"publish","type":"page","link":"https:\/\/www.mysqltutorial.org\/mysql-administration\/mysql-myisam\/","title":{"rendered":"MySQL MyISAM Storage Engine"},"content":{"rendered":"\n<p><strong>Summary<\/strong>: in this tutorial, you will learn about MySQL MyISAM storage engine and its features.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Introduction to MySQL MyISAM storage engine<\/h2>\n\n\n\n<p>MyISAM is a storage engine based on a deprecated ISAM (Indexed Sequential Access Method) storage engine. <\/p>\n\n\n\n<p>MyISAM is a lightweight, non-transactional engine with high performance. It is also easy to copy between systems and has a very small data footprint.<\/p>\n\n\n\n<p>MyISAM was the default storage engine in MySQL until version 5.5 when MySQL changed it to InnoDB. MySQL has also incorporated the major features of MyISAM into <a href=\"https:\/\/www.mysqltutorial.org\/mysql-administration\/mysql-innodb-storage-engine\/\">InnoDB<\/a>, rendering MyISAM somewhat obsolete.<\/p>\n\n\n\n<p>To create a MyISAM table, you use the set the ENGINE clause of the <a href=\"https:\/\/www.mysqltutorial.org\/mysql-basics\/mysql-create-table\/\">CREATE TABLE<\/a> statement to MyISAM:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-1\" data-shcb-language-name=\"SQL (Structured Query Language)\" data-shcb-language-slug=\"sql\"><span><code class=\"hljs language-sql\"><span class=\"hljs-keyword\">CREATE<\/span> <span class=\"hljs-keyword\">TABLE<\/span> table_name(\n   ... \n) <span class=\"hljs-keyword\">ENGINE<\/span>=MYISAM;<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-1\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">SQL (Structured Query Language)<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">sql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>When creating a MyISAM table, the storage engine generates two files with the same name as the table, each having the following extensions:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><code>.MYD<\/code> &#8211; MyData is the data file.<\/li>\n\n\n\n<li><code>.MYI<\/code> &#8211; MyIndex is the index file.<\/li>\n<\/ul>\n\n\n\n<p>The storage engine stores the table definition in the MySQL data dictionary.<\/p>\n\n\n\n<p>MyISAM storage engine does not support transactions, foreign keys, and row locking. Also, the storage limit of a MyISAM table is 256TB.<\/p>\n\n\n\n<p>MyISAM storage engine does support <a href=\"https:\/\/www.mysqltutorial.org\/mysql-full-text-search\/\">full-text search indexes<\/a>, geospatial data type, and indexing.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Converting MyISAM to InnoDB<\/h2>\n\n\n\n<p>If you want to convert all of your tables from MyISAM to InnoDB, you can follow these steps:<\/p>\n\n\n\n<p>First, list all MyISAM tables of a specific database:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-2\" data-shcb-language-name=\"SQL (Structured Query Language)\" data-shcb-language-slug=\"sql\"><span><code class=\"hljs language-sql\"><span class=\"hljs-keyword\">SELECT<\/span> \n  table_name \n<span class=\"hljs-keyword\">FROM<\/span> \n  information_schema.tables \n<span class=\"hljs-keyword\">WHERE<\/span> \n  table_schema = <span class=\"hljs-string\">'database_name'<\/span> \n  <span class=\"hljs-keyword\">AND<\/span> <span class=\"hljs-keyword\">engine<\/span> = <span class=\"hljs-string\">'MyISAM'<\/span>;<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-2\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">SQL (Structured Query Language)<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">sql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>Second, convert each table to InnoDB using the <code>ALTER TABLE<\/code> statement:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-3\" data-shcb-language-name=\"SQL (Structured Query Language)\" data-shcb-language-slug=\"sql\"><span><code class=\"hljs language-sql\"><span class=\"hljs-keyword\">ALTER<\/span> <span class=\"hljs-keyword\">TABLE<\/span> table_name <span class=\"hljs-keyword\">ENGINE<\/span> = <span class=\"hljs-keyword\">InnoDB<\/span>;<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-3\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">SQL (Structured Query Language)<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">sql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>If you need to convert all MyISAM tables in a database to InnoDB, you can use the following stored procedure:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-4\" data-shcb-language-name=\"SQL (Structured Query Language)\" data-shcb-language-slug=\"sql\"><span><code class=\"hljs language-sql\">DELIMITER \/\/\n<span class=\"hljs-keyword\">CREATE<\/span> <span class=\"hljs-keyword\">PROCEDURE<\/span> ConvertMyISAMToInnoDB(<span class=\"hljs-keyword\">IN<\/span> dbName <span class=\"hljs-built_in\">VARCHAR<\/span>(<span class=\"hljs-number\">100<\/span>))\n<span class=\"hljs-keyword\">BEGIN<\/span>\n  <span class=\"hljs-keyword\">DECLARE<\/span> done <span class=\"hljs-built_in\">INT<\/span> <span class=\"hljs-keyword\">DEFAULT<\/span> <span class=\"hljs-literal\">FALSE<\/span>;\n  <span class=\"hljs-keyword\">DECLARE<\/span> tableName <span class=\"hljs-built_in\">VARCHAR<\/span>(<span class=\"hljs-number\">100<\/span>);\n  <span class=\"hljs-keyword\">DECLARE<\/span> cur <span class=\"hljs-keyword\">CURSOR<\/span> <span class=\"hljs-keyword\">FOR<\/span>\n    <span class=\"hljs-keyword\">SELECT<\/span> table_name\n    <span class=\"hljs-keyword\">FROM<\/span> information_schema.tables\n    <span class=\"hljs-keyword\">WHERE<\/span> table_schema = dbName <span class=\"hljs-keyword\">AND<\/span> <span class=\"hljs-keyword\">engine<\/span> = <span class=\"hljs-string\">'MyISAM'<\/span>;\n\n  <span class=\"hljs-keyword\">DECLARE<\/span> CONTINUE <span class=\"hljs-keyword\">HANDLER<\/span> <span class=\"hljs-keyword\">FOR<\/span> <span class=\"hljs-keyword\">NOT<\/span> <span class=\"hljs-keyword\">FOUND<\/span> <span class=\"hljs-keyword\">SET<\/span> done = <span class=\"hljs-literal\">TRUE<\/span>;\n\n  OPEN cur;\n\n  read_loop: LOOP\n    FETCH cur INTO tableName;\n    IF done THEN\n      LEAVE read_loop;\n    <span class=\"hljs-keyword\">END<\/span> <span class=\"hljs-keyword\">IF<\/span>;\n\n    <span class=\"hljs-keyword\">SET<\/span> @alterSql = <span class=\"hljs-keyword\">CONCAT<\/span>(<span class=\"hljs-string\">'ALTER TABLE `'<\/span>, dbName, <span class=\"hljs-string\">'`.`'<\/span>, tableName, <span class=\"hljs-string\">'` ENGINE=InnoDB;'<\/span>);\n    <span class=\"hljs-keyword\">PREPARE<\/span> stmt <span class=\"hljs-keyword\">FROM<\/span> @alterSql;\n    <span class=\"hljs-keyword\">EXECUTE<\/span> stmt;\n    <span class=\"hljs-keyword\">DEALLOCATE<\/span> <span class=\"hljs-keyword\">PREPARE<\/span> stmt;\n  <span class=\"hljs-keyword\">END<\/span> <span class=\"hljs-keyword\">LOOP<\/span>;\n\n  CLOSE cur;\n<span class=\"hljs-keyword\">END<\/span> \/\/\nDELIMITER ;\n<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-4\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">SQL (Structured Query Language)<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">sql<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<p>The stored procedure <code>ConvertMyISAMToInnoDB<\/code> accepts a database name (<code>dbName<\/code>) as a parameter and does the following <\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>First, use a <a href=\"https:\/\/www.mysqltutorial.org\/mysql-cursor\/\">cursor<\/a> to iterate through the list of tables in the specified database (<code>dbName<\/code>) where the engine type is MyISAM <\/li>\n\n\n\n<li>Second, update each table to InnoDB using dynamic SQL.<\/li>\n<\/ul>\n\n\n\n<p>For example, to convert all MyISAM tables in the HR database to InnoDB tables, you call the stored procedure <code>ConvertMyISAMToInnoDB<\/code> like this:<\/p>\n\n\n<pre class=\"wp-block-code\" aria-describedby=\"shcb-language-5\" data-shcb-language-name=\"JavaScript\" data-shcb-language-slug=\"javascript\"><span><code class=\"hljs language-javascript\">CALL ConvertMyISAMToInnoDB(<span class=\"hljs-string\">'HR'<\/span>);<\/code><\/span><small class=\"shcb-language\" id=\"shcb-language-5\"><span class=\"shcb-language__label\">Code language:<\/span> <span class=\"shcb-language__name\">JavaScript<\/span> <span class=\"shcb-language__paren\">(<\/span><span class=\"shcb-language__slug\">javascript<\/span><span class=\"shcb-language__paren\">)<\/span><\/small><\/pre>\n\n\n<h2 class=\"wp-block-heading\">Summary<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Use the MyISAM storage engine for read-heavy workloads and applications that require full-text search capabilities. <\/li>\n\n\n\n<li>MyISAM storage engine doesn&#8217;t support some important features such as transactions and foreign keys, 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