PLSQL中,select case..when.. then..什么意思?怎么用

case when ... then .. when .. then ... end

这种表达式，是sql的不同条件分支结果。

举例如下，

1、创建剞麽苍足数据表，create table test_student(stu_id number, class_id number);

2、插入测试数据，

insert into test_student values(1,1001);

insert into test_student values(2,1001);

insert into test_student values(3,1002);

insert into test_student values(4,1003);

insert into test_student values(5,1003);

insert into test_student values(6,1003);

3、查询表中数据，select * fromtest_student ,

4、编写case when 表达式，将class_id翻译为中文名称，sql如下，

select t.*,

case

when class_id = 1001 then

'语文'

when class_id = 1002 then

'数学'

when class_id = 1003 then

'英语'

end as class_name

from test_student t;