1.drop语句。可以用来删除数据库和表。
A用drop语句来删除数据库：
mysql> drop database hello;Query OK, 0 rows affected (0.19 sec) mysql> show databases; +--------------------+ | Database | +--------------------+ | information_schema | | mysql | | performance_schema | | sys | | test | | trains | +--------------------+ 6 rows in set (0.00 sec)
B用drop语句来删除表：
mysql> drop table q1;Query OK, 0 rows affected (0.39 sec) mysql> show tables; +------------------+ | Tables_in_trains | +------------------+ | 4inall | | ava | | book | | c1score | | c2score | | course | | joke | | sc | | sc1 | | student | | student1 | | teacher | +------------------+ 12 rows in set (0.00 sec)
2.delete语句。用来删除表中的字段：
A通过where子句来指定删除表中的某个记录：
mysql> delete from joke where gid=1; mysql> select * from joke; +------+-----------+-------+------+ | gid | name | sex | age | +------+-----------+-------+------+ | 3 | xiaowan2 | male | 22 | | 3 | xiaowan2 | male | 22 | | 3 | xiaowan2 | male | 22 | | 3 | xiaowan22 | 1male | 22 | | 0 | joker | NULL | NULL | | 0 | joker | NULL | NULL | +------+-----------+-------+------+ 6 rows in set (0.00 sec)
注意：如果delete语句中没有加入where就会把表中的所有记录全部删除：
mysql> select * from student1; +------+--------+------+------+ | s | sname | sage | ssex | +------+--------+------+------+ | 1 | 刘一 | 18 | 男 | | 2 | 钱二 | 19 | 女 | | 3 | 张三 | 17 | 男 | | 4 | 李四 | 18 | 女 | | 5 | 王五 | 17 | 男 | | 6 | 赵六 | 19 | 女 | +------+--------+------+------+ 6 rows in set (0.00 sec) mysql> delete from student1;Query OK, 6 rows affected (0.19 sec) mysql> select * from student1;Empty set (0.00 sec)
B通过select子句来删除表中的某个记录：
mysql> delete from student1 where s in (select s from student where sage=18 and ssex="男");Query OK, 1 row affected (0.13 sec) mysql> select * from student1; +------+--------+------+------+ | s | sname | sage | ssex | +------+--------+------+------+ | 2 | 钱二 | 19 | 女 | | 3 | 张三 | 17 | 男 | | 4 | 李四 | 18 | 女 | | 5 | 王五 | 17 | 男 | | 6 | 赵六 | 19 | 女 | +------+--------+------+------+ 5 rows in set (0.00 sec)
3.用truncate来删除表中的所以字段：
mysql> select * from student1; +------+--------+------+------+ | s | sname | sage | ssex | +------+--------+------+------+ | 1 | 刘一 | 18 | 男 | | 2 | 钱二 | 19 | 女 | | 3 | 张三 | 17 | 男 | | 4 | 李四 | 18 | 女 | | 5 | 王五 | 17 | 男 | | 6 | 赵六 | 19 | 女 | +------+--------+------+------+ 6 rows in set (0.00 sec) mysql> truncate table student1;Query OK, 0 rows affected (0.28 sec) mysql> select * from student1;Empty set (0.00 sec)
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