Review a SQL query for speed and correctness
Reviews a SQL query for wrong results and slow spots, then suggests one rewrite with the reasoning and how to test it safely.
Task:
Review the SQL query below for wrong results and slow spots, and give me one improved version.
Context:
The database is [database engine and version]. The main tables are [table names with row counts]. The query should return [what it should return]. Indexes I know of are [indexes].
Rules:
- Read the whole query and trace the joins and filters before commenting.
- Check for duplicated rows from joins, null handling, filter placement and functions that block index use.
- Say which findings are certain from the query alone and which need the execution plan, and tell me how to get the plan from my engine.
- Do not run or suggest an UPDATE, DELETE or DROP as part of the test. If the query itself writes data, explain what it changes and tell me to try it in a transaction on a copy first.
Result:
A numbered list of at most six findings ranked by impact, then the improved query in one code block. End with one sentence on how to check that both versions return the same rows.
Material:
[paste the SQL query here]