--用于判断expression是固定值CASE[ expression ]WHEN condition1 THEN result1
WHEN condition2 THEN result2
...WHEN conditionn THEN resultn
ELSE result
END-- 示例:select id,name,case age
when12then"12a"when13then"13a"when14then"14a"else"15a"endas age1,case sex
when'boy'then'男'else'女'endas sex1
from stu;
用法2
-- 类似java 的if else if else 写法CASEWHEN condition1 THEN result1
WHEN condition2 THEN result2
...WHEN conditionn THEN resultn
ELSE result
END-- 示例:select id,name,casewhen age =12then"12a"when age =13then"13a"when age =14then"14a"else"15a"endas age1,casewhen sex ='boy'then'男'else'女'endas sex1
from stu;