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    <blockquote> <p>Does placement of join matter?</p> </blockquote> <p>The order they are written does not matter for INNER JOINs.</p> <blockquote> <p>Does order of where clause matter, or will MySQL optimize?</p> </blockquote> <p>No. The written order in a WHERE clause does not matter to the MySQL query parser and optimizer</p> <blockquote> <p>Would and index help in my case?</p> </blockquote> <p>Potentially. A compound index type_status (Type, Status) on table1 could help since that is where your WHERE clause could reduce the initial rows read.</p> <blockquote> <p>Is there any advantage JOINing in the FROM, vs adding 'table1.CurrentName = table2.id' in the WHERE clause?</p> </blockquote> <p>For INNER JOINs, it doesn't matter if the JOIN condition is in the FROM clause or the WHERE clause.</p> <blockquote> <p>I thought adding an index to table1.CurrentName may help, but now I'm thinking not. I modified the query to remove references to table2, and it still ran slow. (see 3b)</p> </blockquote> <p>An index on table1.CurrentName would not help the query.</p> <blockquote> <p>Seems like the bulk of the slowdown may be just reading 800K records looking at the Type and Status values.</p> </blockquote> <p>This reinforces my thought above. To add the compound index (potentially not a good thing to do online), it'd be something like</p> <pre><code>ALTER TABLE table1 ADD INDEX type_status (Type, Status); </code></pre> <blockquote> <p>I thought it only made sense when there were more unique values.</p> </blockquote> <p>Selectivity definitely helps, but high cardinality is not the only suitable context.</p>
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    1. POMySQL - basic 2 table query slow - where, index?
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    1. COGreat and thorough answers, thanks! I'll look into the compound index.
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    2. CODo you really need to select all those rows? I can't imagine a webpage presenting over 700K rows. Don't you miss a LIMIT in your query? However compound/composite index might help a bit.
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    3. CO@ johno, good point. The best data is the data you don't need to pull. :)
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