Migrating Uber from MySQL to PostgreSQL
uber_migration_pypgday_2013
uber_migration_pypgday_2013
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Code Changes<br />
GROUP BY (cont.)<br />
<strong>MySQL</strong> chooses the value of bar by using the first value<br />
encountered, which can be predictable in certain cases<br />
depending on the index the query uses.<br />
There are some advanced use cases for this, but<br />
thankfully all of the queries I found were doing this<br />
unintentionally, without actually relying on this behavior.<br />
Evan Klitzke (<strong>Uber</strong>, Inc.) <strong>Migrating</strong> <strong>Uber</strong> <strong>from</strong> <strong>MySQL</strong> <strong>to</strong> <strong>PostgreSQL</strong> March 13, 2013 47 / 59
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