添加主键mysql> alter table info add primary key(id);Query OK, 0 rows affected (0.07 sec)Records: 0 Dupl
添加主键mysql> alter table info add primary key(id);Query OK, 0 rows affected (0.07 sec)Records: 0 Duplicates: 0 Warnings: 0mysql> desc info; #查看主键+--------+--------------+------+-----+---------+-------+| Field | Type | Null | Key | Default | Extra |+--------+--------------+------+-----+---------+-------+| id | int(11) | NO | PRI | NULL | | #显示出主键| name | char(6) | YES | | NULL | || score | decimal(5,2) | YES | | NULL | || age | int(4) | YES | | NULL | || hobbly | int(4) | YES | | NULL | |+--------+--------------+------+-----+---------+-------+5 rows in set (0.00 sec)添加外键alter table info add constraint FK_ID foreign key(hobbly) REFERENCES hy(id);mysql> show index from info/G; #查看外键* 2. row * Table: info Non_unique: 1 Key_name: FK_ID #外键添加成功 Seq_in_index: 1 Column_name: hobbly Collation: A Cardinality: 3 Sub_part: NULL Packed: NULL Null: YES Index_type: BTREE Comment: Index_comment: 2 rows in set (0.00 sec)表格同时修改个字段（不同表列内容）update info set age=23,num=44 where id=2; mysql> select * from info;+----+--------+-------+-----------+------+------+| id | name | score | hobbly | age | num |+----+--------+-------+-----------+------+------+| 1 | zl | 88 | 看书 | 33 | NULL || 2 | 李四 | 68 | 上网 | 23 | 44 | #成功修改| 3 | 王四 | 68 | 看电视 | NULL | NULL |+----+--------+-------+-----------+------+------+3 rows in set (0.00 sec)同时增加多个字段mysql> alter table info add column age int,add column num int;Query OK, 0 rows affected (0.05 sec)Records: 0 Duplicates: 0 Warnings: 0mysql> desc info; #查看表结构+--------+----------+------+-----+---------+-------+| Field | Type | Null | Key | Default | Extra |+--------+----------+------+-----+---------+-------+| id | int(11) | NO | PRI | NULL | || name | char(4) | YES | | NULL | || score | char(6) | YES | | NULL | || hobbly | char(10) | YES | | NULL | || age | int(11) | YES | | NULL | || num | int(11) | YES | | NULL | |+--------+----------+------+-----+---------+-------+同时删除多个字段mysql> alter table info drop column age,drop column num;Query OK, 0 rows affected (0.05 sec)Records: 0 Duplicates: 0 Warnings: 0mysql> select * from info;+----+--------+-------+-----------+| id | name | score | hobbly |+----+--------+-------+-----------+| 1 | zl | 88 | 看书 || 2 | 李四 | 68 | 上网 || 3 | 王四 | 68 | 看电视 |+----+--------+-------+-----------+同时删除多个记录条数（多行）mysql> delete from info where id in (3,4);Query OK, 2 rows affected (0.00 sec)mysql> select * from info;+----+--------+-------+--------+| id | name | score | hobbly |+----+--------+-------+--------+| 1 | zl | 88 | 看书 || 2 | 李四 | 68 | 上网 || 5 | kl | 88 | 游泳 |+----+--------+-------+--------+同时查看多条指定记录（行）mysql> select * from info where id in (3,4);+----+--------+-------+-----------+| id | name | score | hobbly |+----+--------+-------+-----------+| 3 | 王四 | 68 | 看电视 || 4 | ll | 67 | 看书 |+----+--------+-------+-----------+