Đầu tiên chúng ta hãy tạo một bảng -
mysql> create table DemoTable606 (Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,FirstName varchar(100)); Query OK, 0 rows affected (0.56 sec)
Chèn một số bản ghi vào bảng bằng lệnh chèn -
mysql> insert into DemoTable606(FirstName) values('John');
Query OK, 1 row affected (0.15 sec)
mysql> insert into DemoTable606(FirstName) values('Robert');
Query OK, 1 row affected (0.14 sec)
mysql> insert into DemoTable606(FirstName) values('Chris');
Query OK, 1 row affected (0.13 sec)
mysql> insert into DemoTable606(FirstName) values('David');
Query OK, 1 row affected (0.13 sec) Hiển thị tất cả các bản ghi từ bảng bằng câu lệnh select -
mysql> select *from DemoTable606;
Điều này sẽ tạo ra kết quả sau -
+----+-----------+ | Id | FirstName | +----+-----------+ | 1 | John | | 2 | Robert | | 3 | Chris | | 4 | David | +----+-----------+ 4 rows in set (0.00 sec)
Sau đây là truy vấn để làm việc với lệnh EXPLAIN ::
mysql> explain select * from DemoTable606 order by Id; +----+-------------+--------------+------------+-------+---------------+---------+---------+------+------+----------+-------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+--------------+------------+-------+---------------+---------+---------+------+------+----------+-------+ | 1 | SIMPLE | DemoTable606 | NULL | index | NULL | PRIMARY | 4 | NULL | 4 | 100.00 | NULL | +----+-------------+--------------+------------+-------+---------------+---------+---------+------+------+----------+-------+ 1 row in set, 1 warning (0.00 sec) mysql> explain select * from DemoTable606 order by Id,FirstName; +----+-------------+--------------+------------+------+---------------+------+---------+------+------+----------+----------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+--------------+------------+------+---------------+------+---------+------+------+----------+----------------+ | 1 | SIMPLE | DemoTable606 | NULL | ALL | NULL | NULL | NULL | NULL | 4 | 100.00 | Using filesort | +----+-------------+--------------+------------+------+---------------+------+---------+------+------+----------+----------------+ 1 row in set, 1 warning (0.00 sec) mysql> explain select * from DemoTable606 order by Id,RAND(); +----+-------------+--------------+------------+------+---------------+------+---------+------+------+----------+---------------------------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+--------------+------------+------+---------------+------+---------+------+------+----------+---------------------------------+ | 1 | SIMPLE | DemoTable606 | NULL | ALL | NULL | NULL | NULL | NULL | 4 | 100.00 | Using temporary; Using filesort | +----+-------------+--------------+------------+------+---------------+------+---------+------+------+----------+---------------------------------+ 1 row in set, 1 warning (0.00 sec)