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POMySQL search for user and their roles
 

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    <p>I am re-writing the SQL which lets a user search for any other user on our site and also shows their roles.</p> <p>An an example, roles can be "Writer", "Editor", "Publisher".</p> <p>Each role links a User to a Publication.</p> <p>Users can take multiple roles within multiple publications.</p> <p>Example table setup:</p> <pre><code>"users" : user_id, firstname, lastname "publications" : publication_id, name "link_writers" : user_id, publication_id "link_editors" : user_id, publication_id </code></pre> <p>Current psuedo SQL:</p> <pre><code>SELECT * FROM ( (SELECT user_id FROM users WHERE firstname LIKE '%Jenkz%') UNION (SELECT user_id FROM users WHERE lastname LIKE '%Jenkz%') ) AS dt JOIN (ROLES STATEMENT) AS roles ON roles.user_id = dt.user_id </code></pre> <p>At the moment my roles statement is:</p> <pre><code>SELECT dt2.user_id, dt2.publication_id, dt.role FROM ( (SELECT 'writer' AS role, link_writers.user_id, link_writers.publication_id FROM link_writers) UNION (SELECT 'editor' AS role, link_editors.user_id, link_editors.publication_id FROM link_editors) ) AS dt2 </code></pre> <p>The reason for wrapping the roles statement in UNION clauses is that some roles are more complex and require a table join to find the publication_id and user_id.</p> <p>As an example "publishers" might be linked accross two tables</p> <pre><code>"link_publishers": user_id, publisher_group_id "link_publisher_groups": publisher_group_id, publication_id </code></pre> <p>So in that instance, the query forming part of my UNION would be:</p> <pre><code>SELECT 'publisher' AS role, link_publishers.user_id, link_publisher_groups.publication_id FROM link_publishers JOIN link_publisher_groups ON lpg.group_id = lp.group_id </code></pre> <p>I'm pretty confident that my table setup is good (I was warned off the one-table-for-all system when researching the layout). My problem is that there are now 100,000 rows in the users table and upto 70,000 rows in each of the link tables.</p> <p>Initial lookup in the users table is fast, but the joining really slows things down.</p> <p>How can I only join on the relevant roles?</p> <p>-------------------------- EDIT ---------------------------------- <a href="http://img155.imageshack.us/img155/4758/stackusersearchjoins.gif" rel="nofollow noreferrer">explain http://img155.imageshack.us/img155/4758/stackusersearchjoins.gif</a></p> <p>Explain above (open in a new window to see full resolution).</p> <p>The bottom bit in red, is the "WHERE firstname LIKE '%Jenkz%'" the third row searches WHERE CONCAT(firstname, ' ', lastname) LIKE '%Jenkz%'. Hence the large row count, but I think this is unavoidable, unless there is a way to put an index accross concatenated fields?</p> <p>The green bit at the top just shows the total rows scanned from the ROLES STATEMENT.</p> <p>You can then see each individual UNION clause (#6 - #12) which all show a large number of rows. Some of the indexes are normal, some are unique.</p> <p>It seems that MySQL isn't optimizing to use the dt.user_id as a comparison for the internal of the UNION statements. Is there any way to force this behaviour?</p> <p>Please note that my real setup is not publications and writers but "webmasters", "players", "teams" etc.</p>
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    1. COIt looks like the select statements in the UNION should be restricted with "WHERE user_id = dt.user_id".
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    2. COThanks for your comment Martin. Unfortunately, I can't access the "dt" data from inside my UNION clause. Trying that gives the error "unknown column dt.user_id".
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    3. COI don't think there is anything wrong with the SQL as such - I would expect the join action on user_id between dt and dt2 would perform do the limiting Jenkz talks about. Unless union somehow breaks the normal optimizer. Are you sure the tables have correct indexes? Can you post the output of explain for this query?
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