如何改变MySQL表的列位置而不丢失列数据？

借助 ALTER TABLE 命令，您可以更改 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，让我们创建一个表。创建包含某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)

让我们在表中插入一些数据。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)

现在您可以借助 select 语句来显示所有记录。查询如下 -

mysql> select *from changeColumnPositionDemo;

以下是输出 -

+-----------+----------------+------------+-------------+
| 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)

这里是更改列位置而不丢失数据的查询。我们将“StudentAddress”列移至“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

上面我们在列名StudentAge之后设置了列StudentAddress。

以下是检查上述两列是否已更改且不丢失数据的查询 -

mysql> select *from changeColumnPositionDemo;

以下是输出 -

+-----------+------------+----------------+-------------+
| 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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