【数据库】SQL分组多列统计(GROUP BY后按条件分列统计)
select whbmbh ,zt,1 as tjsl from fyxx group by zt,whbmbh
select whbmbh,sum(case zt when '有效' then 1 end) as yxsl,sum(case zt when '暂缓' then 1 end )as zhsl,sum(case zt when '未知' then 1 end) as wzsl,sum(case zt when '我租' then 1 end) as wzsl,sum(case zt when '他租' then 1 end) as tzsl,sum(case zt when '我售' then 1 end) as wssl,sum(case zt when '他售' then 1 end) as tssl ,sum(case zt when '撤单' then 1 end) as cdsl,sum(case zt when '电话错误' then 1 end) as dhcwsl,sum(case zt when '待确认' then 1 end) as dqrsl,sum(case zt when '已驳回' then 1 end) as ybhsl from fyxx group by whbmbh
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最近遇到一个问题,需要对一张表做统计,这个统计有什么特别之处值得我记录了下来呢?大家知道SQL中聚合函数GROUP BY的结果一般为一列,即多个值通过聚合函数运算统计到一起,但是如何将不同条件的值统计到不同列中呢,即按条件统计到多个列中。举个栗子:
YEAR | TYPE | VALUE |
2015 | 1 | 100 |
2015 | 2 | 200 |
2016 | 1 | 150 |
2016 | 2 | 300 |
2016 | 3 | 100 |
转为:
YEAR | TYPE1 | TYPE2 | TYPE3 |
2015 | 100 | 200 | 0 |
2016 | 150 | 300 | 100 |
这时候我们除了用到GROUP BY之外还需要CASE WHEN,SQL如下:
SELECT year, SUM(CASE WHEN type=1 THEN value ELSE 0 END) as type1, SUM(CASE WHEN type=2 THEN value ELSE 0 END) as type2, SUM(CASE WHEN type=3 THEN value ELSE 0 END) as type3, FROM table_test GROUP BY year