What is EXPLAIN Plan
EXPLAIN Plan is a command in SQL used to display the execution plan of a query, showing how the database engine plans to execute the query, including the order of operations and indexes used, which helps in optimizing performance.
Example: SQL Query with EXPLAIN Plan
MySQL
EXPLAIN SELECT * FROM customers WHERE customer_id = 1;PostgreSQL
EXPLAIN (ANALYZE, VERBOSE) SELECT * FROM customers WHERE customer_id = 1;SQLite
EXPLAIN QUERY PLAN SELECT * FROM customers WHERE customer_id = 1;Output Interpretation
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | SIMPLE | customers | NULL | const | PRIMARY | PRIMARY | 4 | const | 1 | 100.00 | Using index |
Example: Understanding the Plan
MySQL
EXPLAIN SELECT c.name, o.order_date
FROM customers c
JOIN orders o ON c.customer_id = o.customer_id
WHERE c.customer_id = 1;PostgreSQL
EXPLAIN (ANALYZE, VERBOSE)
SELECT c.name, o.order_date
FROM customers c
JOIN orders o ON c.customer_id = o.customer_id
WHERE c.customer_id = 1;SQLite
EXPLAIN QUERY PLAN
SELECT c.name, o.order_date
FROM customers c
JOIN orders o ON c.customer_id = o.customer_id
WHERE c.customer_id = 1;