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POCorrelated subqueries in MySql - how to evaluate outer query first?
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  1. POCorrelated subqueries in MySql - how to evaluate outer query first?
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    copied!<p>I am having problems with subqueries in MySql. I have a table containing user groups. The columns are id, name and the properties with a comment describing each row: (Id is INT, Name VARCHAR, all other TINYINT(1) (boolean that is)</p> <pre><code>ID | Name | login | post | manage 1 user 1 0 0 2 poster 1 1 0 3 admin 1 1 1 </code></pre> <p>My goal is to be able to list the usergroup properties (login, post and manage above) and the number of usergroups that has each property (3, 2 and 1 respectively).</p> <p>This query works (but obviously counts the login column every time):</p> <pre><code>SELECT @colname:=cols.column_name,cols.column_comment, (SELECT COUNT(*) FROM db.usergroups WHERE login=1) AS num_users FROM information_schema.columns AS cols WHERE TABLE_SCHEMA='db' AND TABLE_NAME='usergroups' AND column_type='tinyint(1)'; </code></pre> <p>This does not work (num_users is always 0)</p> <pre><code>SELECT @colname:=cols.column_name,cols.column_comment, (SELECT COUNT(*) FROM db.usergroups WHERE cols.column_name=1) AS num_users FROM information_schema.columns AS cols WHERE TABLE_SCHEMA='db' AND TABLE_NAME='usergroups' AND column_type='tinyint(1)'; </code></pre> <p>This neither (num_users is always 0)</p> <pre><code>SELECT @colname:=cols.column_name,cols.column_comment, (SELECT COUNT(*) FROM db.usergroups WHERE @colname=1) AS num_users FROM information_schema.columns AS cols WHERE TABLE_SCHEMA='db' AND TABLE_NAME='usergroups' AND column_type='tinyint(1)'; </code></pre> <p>Is there any way to get this to work? That is - to evaluate the outer statement first?</p> <p>-</p> <p>Thanks a lot for any help!</p> <p>/Victor</p>
 

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