SQL语句case关键字的用法

SELECT testName, testSex, 
CASE testSex 
　　WHEN ‘1‘ THEN ‘男‘ 
　　WHEN ‘0‘ THEN ‘女‘
END Sex
FROM testDataTable 

SELECT testName, testDatetime,
CASE  
    WHEN testDatetime < ‘2016-04-11‘ THEN ‘old‘ 
    ELSE ‘new‘  
END Datetime 
FROM testDataTable 

SELECT COUNT(CASE 
    WHEN testSex=‘1‘ THEN 1 
    ELSE NULL    --这里要用NULL，不能用0
END )男生总数 FROM testDataTable