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POMysql Index Being Ignored
 

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    <pre><code>EXPLAIN SELECT * FROM content_link link STRAIGHT_JOIN content ON link.content_id = content.id WHERE link.content_id = 1 LIMIT 10; +----+-------------+---------+-------+---------------+------------+---------+-------+------+-------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+---------+-------+---------------+------------+---------+-------+------+-------+ | 1 | SIMPLE | link | ref | content_id | content_id | 4 | const | 1 | | | 1 | SIMPLE | content | const | PRIMARY | PRIMARY | 4 | const | 1 | | +----+-------------+---------+-------+---------------+------------+---------+-------+------+-------+ </code></pre> <p>However, when I remove the WHERE, the query stops using the key (even when i explicitly force it to)</p> <pre><code>EXPLAIN SELECT * FROM content_link link FORCE KEY (content_id) STRAIGHT_JOIN content ON link.content_id = content.id LIMIT 10; +----+-------------+---------+--------+---------------+---------+---------+------------------------+---------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+---------+--------+---------------+---------+---------+------------------------+---------+-------------+ | 1 | SIMPLE | link | index | content_id | PRIMARY | 7 | NULL | 4555299 | Using index | | 1 | SIMPLE | content | eq_ref | PRIMARY | PRIMARY | 4 | ft_dir.link.content_id | 1 | | +----+-------------+---------+--------+---------------+---------+---------+------------------------+---------+-------------+ </code></pre> <p>Are there any work-arounds to this?</p> <p>I realize I'm selecting the entire table in the second example, but why does mysql suddenly decide that it's going to ignore my FORCE anyway and not use the key? Without the key the query takes like 10 minutes.. ugh.</p>
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    1. USIan Elliott
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      1. USMatthew Christensen
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    1. COI don't understand your question. Is your actual use-case suffering? Sometimes the test SQL you run will have different run paths than the code that's in production. Maybe you're making an incorrect assumption somewhere such that this course of action is indeed correct. Is your data indexed properly?
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      1. USMark Canlas
    2. CODoes your content_id accept NULL values?
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      1. USQuassnoi
 

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