1、行转列问题
1 select year,sum(case when month<=3 then sale else 0 end) as '第一季度', 2 sum(case when (month>3 and month<=6) then sale else 0 end) as '第二季度', 3 sum(case when (month>6 and month<=9) then sale else 0 end) as '第三季度', 4 sum(case when (month>9 and month<=12) then sale else 0 end) as '第四季度' 5 from sales group by Year;
2、有A(id,sex,par,c1,c2),B(id,age,c1,c2)两张表，其中A.id与B.id关联，现在要求写一条SQL语句，将B中age>50的记录的c1、c2更新到A表中统一记录中的c1、c2字段中。
答案：
1 update a inner join b on a.id=b.id and b.age>50 set a.c1=b.c1,a.c2=b.c2;
