关于Mysql子查询的三个应用场景

-- 先找出当日累计购买金额在100-200之间的会员
SELECT dimMemberID 
      ,SUM(AMT) as money
FROM dw.fct_sales
where dimDateID ='20170702'
and dimMemberID <> 0
group by dimMemberID
-- having sum(AMT)>100 and sum(AMT)<200;
having money BETWEEN 100 and 200;
-- 用查找出来的会员做过滤条件，查找消费记录
SELECT *
FROM dw.fct_sales
where dimDateID = '20170702'
and dimMemberID <>0
and dimMemberID in (
                    SELECT dimMemberID 
                       -- ,SUM(AMT) as money    子查询在where后面，当做一个过滤条件,这个字段也必须有且只有一个,所以最后结果要返回过滤条件
                    FROM dw.fct_sales
                    where dimDateID ='20170702'
                    and dimMemberID <> 0
                    group by dimMemberID
                    having sum(AMT)>100 and sum(AMT)<200);
                    -- having money BETWEEN 100 and 200 );  不能直接用命名的列名money，要写全函数，因为前面语句没有出现money，所以为了避免报错，之后尽量写全函数

-- 1、统计2017年7月2日每位会员的累计购买金额
SELECT dimMemberID 
      ,SUM(AMT) as money 
FROM dw.fct_sales
where dimDateID = '20170702'
and dimMemberID <> 0
group by dimMemberID ;
-- 2、把第一步统计出来的数据作为临时表，对统计出来的数据进行分段
SELECT dimMemberID 
      ,money 
      ,case when money <100 then 'D'
            when money >=100 and money <500 then 'C'
            when money >=500 and money <1000 then 'B'
            when money >=1000 then 'A'
            else '其它'
       end as type1
FROM (SELECT dimMemberID                      /*临时表可以生成多个字段，并不是每个字段都需要用也行*/
            ,SUM(AMT) as money 
      FROM dw.fct_sales
      where dimDateID = '20170702'
      and dimMemberID <> 0
      group by dimMemberID) as sn;            /*子查询在from后面做临时表来用,必须给这个子查询生成的临时表取一个表的别名，否则会报错*/

-- 1、2017年7月2日每个会员购买金额
SELECT dimMemberID 
      ,SUM(AMT) as money
FROM dw.fct_sales
where dimDateID = '20170702'
and dimMemberID <>0                   /*去除非会员,即 dimMemberID 为 0 的数据*/
group by dimMemberID ;
-- 2、总体金额
SELECT SUM(AMT) 
FROM dw.fct_sales
where dimDateID = '20170702';
-- 3、合并两个表   注意在合并时where的条件要写全，不要遗漏，不然容易出现逻辑错误
SELECT dimMemberID 
      ,SUM(AMT) as money
      ,(SELECT SUM(AMT)                                /*统计总金额*/
        FROM dw.fct_sales
        where dimDateID = '20170702'
        and dimMemberID<>0) as total_money
      ,CONCAT(                                         /*加上%号*/
       ROUND(                                          /*四舍五入保留4位小数，带%一定要思考保留小数位数*/
       SUM(AMT)/(SELECT SUM(AMT) 
                 FROM dw.fct_sales
                 where dimDateID = '20170702'
                 and dimMemberID<>0),4)*100,'%') 
       as member_rate                                  /*合并表，统计占比*/
FROM dw.fct_sales
where dimDateID = '20170702'
and dimMemberID <>0                                    /*去除非会员,即 dimMemberID 为 0 的数据*/
group by dimMemberID ;