a first form
1 Grammar
CASE column_name
WHEN value1 THEN result1,...
[ELSE result] END
2 codes
SQL>select*from users;
ID USERNAME SALARY
----------------------------------------
1 aaa 800
2 bbb 1800.5
3 cccc 5000.5
4 aaa 1000
SQL>select username,case username when'aaa'then'计算机部门'
2when'bbb'then'市场部门'else'其他部门'endas部门
3from users;
USERNAME 部门
------------------------------
aaa 计算机部门
bbb 市场部门
cccc 其他部门
aaa 计算机部门
The second form
1 Grammar
case
WHEN column_name=value1
THEN result1,...[ELSE result] END
2 code
SQL>select username,casewhen username ='aaa'then'计算机部门'
2when username='bbb'then'市场部门'else'其他部门'endas部门
3from users;
USERNAME 部门
------------------------------
aaa 计算机部门
bbb 市场部门
cccc 其他部门
aaa 计算机部门
SQL>select username,casewhen salary<800then'low'
2when salary>5000then'high'endas工资水平
3from users;
USERNAME 工资
------------------------
aaa
bbb
cccc high
aaa