数据库

虽然学得挺烂的，但还是记个笔记吧

4

4.6where子句子查询

1. in 子查询
2. 比较子查询
   {>,<,=/all/some/any}
   3.EXISTS 子查询

4.6 FROM 子句子查询

4.6 SELECT 子句子查询

SELECT sno,sname,year(sbirth)-year(( SELECT sbirth from  xs  
WHERE   
sno = 1001)) as 年龄差距 
from xs 
WHERE ssex = '女'

SELECT sno,sname
from xs
WHERE(ssex,zxf) = (
    SELECT ssex,zxf
    from xs
    WHERE sno = '1001'
)


SELECT  zy,count(*) as '学生数'
from    xs
group by zy;

SELECT zy,ssex,COUNT(*) AS 总人数
FROM xs
GROUP BY zy, ssex WITH ROLLUP;