添加主键mysql> alter table info add primary key(id);Query OK, 0 rows affected (0.07 sec)Records: 0Duplicates: 0Warnings: 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: 1Column_name: hobblyCollation: ACardinality: 3 Sub_part: NULL Packed: NULL Null: YES Index_type: BTREEComment: 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: 0Duplicates: 0Warnings: 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: 0Duplicates: 0Warnings: 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|+----+--------+-------+-----------+