MySQL EXPLAIN输出列的详细解释

1. 简介

EXPLAIN语句提供有关 MySQL 如何执行语句的信息。

EXPLAIN与SELECT、DELETE、INSERT、REPLACE和UPDATE语句一起使用。

mysql> EXPLAIN SELECT * FROM employees WHERE emp_no = 10001;
+----+-------------+-----------+------------+-------+---------------+---------+---------+-------+------+----------+-------+
| id | select_type | table     | partitions | type  | possible_keys | key     | key_len | ref   | rows | filtered | Extra |
+----+-------------+-----------+------------+-------+---------------+---------+---------+-------+------+----------+-------+
|  1 | SIMPLE      | employees | NULL       | const | PRIMARY       | PRIMARY | 4       | const |    1 |   100.00 | NULL  |
+----+-------------+-----------+------------+-------+---------------+---------+---------+-------+------+----------+-------+
1 row in set, 1 warning (0.00 sec)