CompTIA DataSys+ (DS0-001)Database FundamentalsHard
A database administrator is routinely performing maintenance tasks. They need to analyze the performance of a specific SQL query, including how it accesses data, which indexes it uses, and the estimated cost of each operation. Which SQL DDL/DML command or statement prefix would provide this detailed information?
- AANALYZE TABLE
- BSHOW INDEXES
- CEXPLAIN (or EXPLAIN ANALYZE)
- DOPTIMIZE TABLE
Show answer & explanationAnswer & explanation
Correct answer: C. EXPLAIN (or EXPLAIN ANALYZE)
`EXPLAIN` (or `EXPLAIN PLAN` in Oracle, `EXPLAIN ANALYZE` in PostgreSQL) is a crucial SQL command used to view the execution plan of a query. It details how the database will process the query, including join orders, index usage, and estimated costs, which is essential for performance tuning.
Why the other options are wrong
- A. `ANALYZE TABLE` collects statistics about a table for the query optimizer, but doesn't show the execution plan of a specific query.
- B. `SHOW INDEXES` lists available indexes on a table, but doesn't analyze a specific query's execution plan.
- D. `OPTIMIZE TABLE` attempts to reclaim unused space and defragment data, improving physical storage, but doesn't analyze query plans.
EXPLAIN Statement
A SQL command used to display the execution plan of a given SQL statement, detailing how the database will process the query.
- Shows join order, index usage, table scans, and estimated costs.
- Crucial tool for query performance tuning and optimization.
- Syntax varies slightly by database system (e.g., `EXPLAIN PLAN`, `EXPLAIN ANALYZE`).
Memory trick: EXPLAIN 'Explains' the query's 'Plan'.