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POPerformant Way to List Foreign Keys for a MySQL Table?
 

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    <p>Is there a <strong>performant</strong> way to fetch the list of foreign keys assigned to a MySQL table?</p> <p>Querying the information schema with </p> <pre><code>SELECT `column_name`, `referenced_table_schema` AS foreign_db, `referenced_table_name` AS foreign_table, `referenced_column_name` AS foreign_column FROM `information_schema`.`KEY_COLUMN_USAGE` WHERE `constraint_schema` = SCHEMA() AND `table_name` = 'your-table-name-here' AND `referenced_column_name` IS NOT NULL ORDER BY `column_name`; </code></pre> <p>works, but is painfully slow on the versions of MySQL I've tried it with. A bit of research turned up <a href="http://bugs.mysql.com/bug.php?id=19588" rel="nofollow">this bug</a>, which seems to indicate it's an ongoing issue without a clear solution. The solutions which are hinted at require reconfiguring or recompiling mysql with a patch, which doesn't work for the project I'm working on.</p> <p>I realize it's possible to issue the following</p> <pre><code>SHOW CREATE TABLE table_name; </code></pre> <p>and get a string representation of a CREATE TABLE statement, which will include the foreign key constraints. However, parsing this string seems like it would be fragile, and I don't have a large corpus of CREATE TABLE statements to test against. (if there's a standard bit of parsing code for this out there, I'd love some links)</p> <p>I also realize I can list the indexes with the following</p> <pre><code>SHOW CREATE TABLE table_name; </code></pre> <p>The list of indexes will include the foreign keys, but there doesn't appear to be a way to determine which of the indexes are foreign keys, and which are "regular" MySQL indexes. Again, some cross referencing with the SHOW CREATE table information could help here, but that brings us back to fragile string parsing.</p> <p>Any help, or even links to other smart discussions on the issue, would be appreciated. </p>
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    1. USAlan Storm
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    1. COI don't see why it would be fragile to write a simple parser for the foreign key part of a create table... create table syntax is clearly defined in the mysql docs...
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      1. USZak
    2. COI'm curious why performance would matter in a query like this. It's not that you want to investigate the database structure 50 times a second, and if you do, there's something horribly wrong with your application.
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    3. CO@Zak It's a philosophical thing, but I suspect that's ultimately what I'll need to do. I'm wary of edge cases not covered in the docs, I'm wary of mysql versions whose SHOW CREATE TABLE syntax may return something back that's not valid syntax, and I'm there's no way to overcome that wariness without putting in the time first.
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