极客教程MySQL 如何在不丢失列数据的情况下更改表的列位置
您可以通过使用ALTER TABLE命令来更改MySQL表的列位置而不会丢失数据。语法如下：
ALTER TABLE yourTableName MODIFY yourColumnName1 data type AFTER yourColumnName2;
为了理解上述概念，让我们创建一张表。创建带有一些列的表的查询如下：
mysql> create table changeColumnPositionDemo
−> (
−> StudentId int,
−> StudentAddress varchar(200),
−> StudentAge int,
−> StudentName varchar(200)
−> );
Query OK, 0 rows affected (0.72 sec)
让我们向表中插入一些数据。插入记录的查询如下 -。
mysql> insert into changeColumnPositionDemo values(101,'US',23,'Johnson');
Query OK, 1 row affected (0.13 sec)
mysql> insert into changeColumnPositionDemo values(102,'UK',20,'John');
Query OK, 1 row affected (0.19 sec)
mysql> insert into changeColumnPositionDemo values(103,'US',22,'Carol');
Query OK, 1 row affected (0.39 sec)
mysql> insert into changeColumnPositionDemo values(104,'UK',19,'Sam');
Query OK, 1 row affected (0.18 sec)
现在您可以使用select语句显示所有记录。查询如下 –
mysql> select *from changeColumnPositionDemo;
输出如下：
+-----------+----------------+------------+-------------+
| StudentId | StudentAddress | StudentAge | StudentName |
+-----------+----------------+------------+-------------+
| 101 | U | 23 | Johnson |
| 102 | UK | 20 | John |
| 103 | US | 22 | Carol |
| 104 | UK | 19 | Sam |
+-----------+----------------+------------+-------------+
4 rows in set (0.00 sec)
这是在不丢失数据的情况下更改列位置的查询。我们将“StudentAddress”列移动到“StudentAge”列之后 –
mysql> ALTER TABLE changeColumnPositionDemo MODIFY StudentAddress varchar(200) AFTER StudentAge;
Query OK, 0 rows affected (2.27 sec)
Records: 0 Duplicates: 0 Warnings: 0
上面我们设置了StudentAddress列在StudentAge列之后。
以下是检查上述两个列是否已更改而不丢失数据的查询 –
mysql> select *from changeColumnPositionDemo;
输出如下 –
+-----------+------------+----------------+-------------+
| StudentId | StudentAge | StudentAddress | StudentName |
+-----------+------------+----------------+-------------+
| 101 | 23 | US | Johnson |
| 102 | 20 | UK | John |
| 103 | 22 | US | Carol |
| 104 | 19 | UK | Sam |
+-----------+------------+----------------+-------------+
4 rows in set (0.00 sec)
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