Q50: What step-by-step methodology do you follow to optimize a slow SQL query?
Follow this step-by-step engineering checklist to diagnose and optimize slow database queries:
Query Optimization Step-by-Step Checklist
Step 1: Inspect Execution Plan:
Run EXPLAIN ANALYZEIdentify sequential scans, nested loop bottlenecks, and memory spill warnings.
Step 2: Ensure SARGability:
Fix Predicate LogicRemove scalar function wrappers around indexed search columns.
Step 3: Indexing Strategy:
Add Covering / Composite IndexesCreate targeted index structures to avoid unnecessary full table scans.
Step 4: Reduce Payload:
Eliminate SELECT *Retrieve only required columns to reduce memory overhead and network payload size.
Key Takeaways
- Always inspect actual execution plans using
EXPLAIN ANALYZEbefore changing indexes. - Select only required columns to minimize network payload and avoid memory spills.