Database Indexing easy
What is the purpose of running `EXPLAIN SELECT ...`?
- A To verify the lexical and syntactic correctness of the SQL statement without actually connecting to the database engine.
- B To execute the query in a temporary sandbox environment and immediately rollback all changes to ensure data safety.
- C To manually add the query and its estimated results to the database's internal high-speed memory cache for future reuse.
- D To view the Query Execution Plan, which reveals the chosen indexes, estimated row counts, and join algorithms.
Answer: D. To view the Query Execution Plan, which reveals the chosen indexes, estimated row counts, and join algorithms.
The `EXPLAIN` command is the most important tool for database performance tuning. It allows developers to see exactly how the database optimizer intends to execute a query. By analyzing the plan, you can identify if the database is performing a slow 'Full Table Scan' when it should be using an index, or if it is joining tables in an inefficient order. Tuning a query always begins with understanding its execution plan.
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