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修改表结构：
alter [ignore] table <table specification> <table structure change>
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包括表属性改变，列属性改变，完整性约束改变。1.表属性改变
1.1重命名表名
mysql> alter table student rename to s;Query OK, 0 rows affected (0.03 sec)
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mysql> rename table s to student;Query OK, 0 rows affected (0.13 sec)
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1.2表排序改变
mysql> alter table student order by stu_id desc;mysql> select * from student;+--------+----------+---------+-----------+| stu_id | stu_name | stu_tel | stu_score |+--------+----------+---------+-----------+| 4 | d | 154 | 63 || 3 | c | 153 | 62 || 2 | b | 152 | 61 || 1 | a | 151 | 60 |+--------+----------+---------+-----------+
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2列属性改变
2.1 添加列
mysql> alter table student -> add sex char(1) after stu_name;Query OK, 4 rows affected (0.34 sec)Records: 4 Duplicates: 0 Warnings: 0mysql> select * from student;+--------+----------+------+---------+-----------+| stu_id | stu_name | sex | stu_tel | stu_score |+--------+----------+------+---------+-----------+| 1 | a | NULL | 151 | 60 || 2 | b | NULL | 152 | 61 || 3 | c | NULL | 153 | 62 || 4 | d | NULL | 154 | 63 |+--------+----------+------+---------+-----------+4 rows in set (0.02 sec)
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2.2删除列
mysql> alter table student -> drop sex;Query OK, 4 rows affected (0.33 sec)Records: 4 Duplicates: 0 Warnings: 0
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2.3修改列属性
初始列属性：+-------------+-----------+| column_name | data_type |+-------------+-----------+| stu_id | int || stu_name | varchar || stu_tel | int || stu_score | int |+-------------+-----------+
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mysql> alter table student -> change stu_tel tel char(3) after stu_score;;Query OK, 4 rows affected (0.23 sec)+-------------+-----------+| column_name | data_type |+-------------+-----------+| stu_id | int || stu_name | varchar || stu_score | int || tel | char |+-------------+-----------+
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将tel列改回int型mysql> alter table student -> modify tel int(3);Query OK, 4 rows affected (0.25 sec)Records: 4 Duplicates: 0 Warnings: 0+-------------+-----------+| column_name | data_type |+-------------+-----------+| stu_id | int || stu_name | varchar || stu_score | int || tel | int |+-------------+-----------+
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3.完整性约束改变
<integrity constraint change>:=add primary key<index name>add unique <index name>add foreign key <index name>(column list) referencing <specification>add check <condition>drop primary keydrop foreign key <index name>drop constraint <constraint name>
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删除主键：mysql> alter table student drop primary key;
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mysql> alter table student add primary key(stu_id);
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