Why does this SQL ORDER BY in subquery get ignored?
Why does this SQL ORDER BY in subquery get ignored. The SQL code uses ORDER BY inside a derived table. In MySQL without LIMIT the optimizer ignores it. In SQL the order you expect is not the order you get.
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How to Stop Bulk INSERT From Locking the Table Forever
Big inserts can block every other query.
How to Use IGNORE INDEX When Optimizer Picks Wrong Plan
MySQL sometimes chooses the slow path.
How to Stop Decimal Precision From Losing Money
Floating point can silently drop cents.
Why does this SQL phantom read show rows that vanish?
Why does this SQL phantom read show rows that vanish. The SQL code runs REPEATABLE READ. In MySQL another transaction can insert matching rows. In SQL you see rows in one read that disappear in the next.
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Why does this SQL ORDER BY RAND() melt the database?
Why does this SQL ORDER BY RAND() melt the database. The SQL code uses ORDER BY RAND() for random rows. In MySQL that sorts the entire table. In SQL one query can take down the server.
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How to Stop MySQL From Scanning With FIND_IN_SET
FIND_IN_SET bypasses indexes and burns CPU.
Why does this SQL SUM return NULL for empty?
Why does this SQL SUM return NULL for empty result. The SQL code sums a column without COALESCE. In SQL SUM of zero rows returns NULL not zero. In SQL APIs this breaks calculations and causes NaN downstream.
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How to Prevent Slow Query Log From Filling Your Disk
One bad query. Millions of log lines.
