如何通过交换两个列值来更新 MySQL 表?
mysqlmysqli database
要交换列中的两个值，请使用 CASE WHEN 语句。让我们首先创建一个表−
mysql> create table DemoTable1382 -> ( -> StudentName varchar(20) -> ); Query OK, 0 rows affected (0.57 sec)
使用 insert 命令在表中插入一些记录 −
mysql> insert into DemoTable1382 values('John');
Query OK, 1 row affected (0.17 sec)
mysql> insert into DemoTable1382 values('Chris');
Query OK, 1 row affected (0.11 sec)
mysql> insert into DemoTable1382 values('Adam');
Query OK, 1 row affected (0.11 sec)
mysql> insert into DemoTable1382 values('Bob');
Query OK, 1 row affected (0.17 sec)
使用 select 语句显示表中的所有记录 −
mysql> select * from DemoTable1382;
这将产生以下输出 −
+-------------+ | StudentName | +-------------+ | John | | Chris | | Adam | | Bob | +-------------+ 4 rows in set (0.00 sec)
以下是通过交换两个列值来更新 MySQL 表的查询 −
mysql> update DemoTable1382 -> set StudentName=( case when StudentName="Chris" then "John" -> when StudentName="John" then "Chris" -> else -> StudentName -> end -> ); Query OK, 2 rows affected (0.19 sec) Rows matched: 4 Changed: 2 Warnings: 0
让我们再次检查表记录 −
mysql> select * from DemoTable1382;
这将产生以下输出 −
+-------------+ | StudentName | +-------------+ | Chris | | John | | Adam | | Bob | +-------------+ 4 rows in set (0.00 sec)
