LarrySequino SQL Query Review
Two questions, in order: is it correct, and what does it do to everyone else.
Procedure
- Read the joins before anything else. A missing join predicate is a cross join with a plausible-looking result, and it is the error that survives review most often.
- Get the plan. A sequential scan on a large table, a nested loop over millions of rows, or a sort that spills to disk each need a different fix.
- Look for predicates that defeat an index: a function on the column, a leading wildcard, or a comparison across mismatched types.
- Check what it writes and how long it holds. An update touching a million rows in one transaction blocks writers and grows the undo log; batch it.
- Confirm the statement is bounded. No limit, no date filter, and no key predicate together mean the result grows until the day it does not fit.
- Say when it is safe to run: any time, off peak, or maintenance window only.
Output
The correctness findings first, then the cost findings, then a verdict with a recommended window and a batch size if the statement writes.