在If-Else语句中,根据值将条件评估为true或false。
让我们来看一个例子。首先,我们将创建一个表。CREATE命令用于创建表。mysql> create table IfelseDemo
- > (
- > id int,
- > FirstName varchar(100)
- > );
在INSERT命令的帮助下插入记录。mysql> insert into IfelseDemo values(1,'John');
mysql> insert into IfelseDemo values(2,'Carol');
mysql> insert into IfelseDemo values(3,'John');
mysql> insert into IfelseDemo values(4,'Carol');
mysql> insert into IfelseDemo values(5,'John');
显示所有记录。mysql> select *from IfelseDemo;
这是我们的输出。+------+-----------+
| id | FirstName |
+------+-----------+
| 1 | John |
| 2 | Carol |
| 3 | John |
| 4 | Carol |
| 5 | John |
+------+-----------+
5 rows in set (0.00 sec)
以下是使用if-else语句的查询。mysql> SELECT id, FirstName, (case when (id = 2 and FirstName = 'Carol')
- > then
- > 'Welcome Carol'
- > else
- > 'You are not Carol with id 2'
- >end)as Message from IfelseDemo;
以下是输出。+------+-----------+-----------------------------+
| id | FirstName | Message |
+------+-----------+-----------------------------+
| 1 | John | You are not Carol with id 2 |
| 2 | Carol | Welcome Carol |
| 3 | John | You are not Carol with id 2 |
| 4 | Carol | You are not Carol with id 2 |
| 5 | john | You are not Carol with id 2 |
+------+-----------+-----------------------------+
5 rows in set (0.00 sec)