mysql中关于删除语句大全总结（下）

A update set 与where搭配使用，变更某些记录：

update +表名 +set+ 变更后的信息 +where子句；

例如：

update stu set birth=1988,department='中文系' where id=9 and name='张三';

注意：如果变更信息后面没有加where子句指定其变更的内容，那么update set语句就会把这个字段中的所有信息全部更新，修改。

例如

mysql> select * from c1score;
+-------+------+
| score | s |
+-------+------+
| 56 | 1 |
| 79 | 2 |
| 91 | 3 |
| 46 | 5 |
| 35 | 6 |
+-------+------+
5 rows in set (0.08 sec)
mysql> update c1score set score=score+8;
Query OK, 5 rows affected (0.13 sec)
Rows matched: 5 Changed: 5 Warnings: 0
mysql> select * from c1score;
+-------+------+
| score | s |
+-------+------+
| 64 | 1 |
| 87 | 2 |
| 99 | 3 |
| 54 | 5 |
| 43 | 6 |
+-------+------+ 
5 rows in set (0.00 sec)

5用alter语句来删除字段：

A alter table 表名 drop 字段名；

mysql> alter table c1score drop s;
Query OK, 0 rows affected (1.80 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> select * from c1score;
+-------+
| score |
+-------+
| 64 |
| 87 |
| 99 |
| 54 |
| 43 |
+-------+
5 rows in set (0.00 sec)

B 用alter来删除索引：

mysql> drop index idx_4a on 4a; 
Query OK, 0 rows affected (0.41 sec) 
Records: 0 Duplicates: 0 Warnings: 0

C 用alter来删除主键：

mysql> alter table sc3 drop primary key;
Query OK, 17 rows affected (1.00 sec)
Records: 17 Duplicates: 0 Warnings: 0

D 用alter来删除，更新表名：

mysql> alter table sc3 rename to gyssc;
Query OK, 0 rows affected (0.30 sec)
mysql> select * from sc3;
ERROR 1146 (42S02): Table 'trains.sc3' doesn't exist