修改表結構：
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包括表屬性改變，列屬性改變，完整性約束改變。
1.表屬性改變
1.1重命名表名
? 1 2 mysql> alter table student rename to s; Query OK, 0 rows affected (0.03 sec)也可以直接使用rename命令改名：
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1 2 mysql> rename table s to student; Query OK, 0 rows affected (0.13 sec)1.2表排序改變
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1 2 3 4 5 6 7 8 9 10 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 | +--------+----------+---------+-----------+2列屬性改變
2.1 添加列
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 mysql> alter table student -> add sex char(1) after stu_name; Query OK, 4 rows affected (0.34 sec) Records: 4 Duplicates: 0 Warnings: 0 mysql> 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)新添加的列默認放在最後一列，且默認填充空值。這裡使用after指定了新增列sex放在stu_name後面.如果新增列設置不能為空，那麼mysql將根據列的數據類型填入實際的值：對於數值填入0，對於字符串填入空字符串，對於日期填入0000-00-00，對於時間填入00:00:00.
2.2刪除列
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1 2 3 4 mysql> alter table student -> drop sex; Query OK, 4 rows affected (0.33 sec) Records: 4 Duplicates: 0 Warnings: 02.3修改列屬性
初始列屬性：
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1 2 3 4 5 6 7 8 +-------------+-----------+ | column_name | data_type | +-------------+-----------+ | stu_id | int | | stu_name | varchar | | stu_tel | int | | stu_score | int | +-------------+-----------+將stu_tel列修改為tel char型，並放在stu_score後面。
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1 2 3 4 5 6 7 8 9 10 11 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 | +-------------+-----------+如果僅僅是更改列其他屬性而不改列名時，可以使用modify參數。
將tel列改回int型
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1 2 3 4 5 6 7 8 9 10 11 12 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 | +-------------+-----------+3.完整性約束改變
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1 2 3 4 5 6 7 8 <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 key drop foreign key <index name> drop constraint <constraint name> 在add後面可以添加[constraint
刪除主鍵：
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1 mysql> alter table student drop primary key;添加主鍵：
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1 mysql> alter table student add primary key(stu_id);
