从两个不同的表中收集数据，Sql

Question

我有两个单独的表格，分别代表两周的学生出勤率。我想生成两列，按周划分每个学生的出勤率。如果学生每周多次出现，则应添加出现次数。此外，如果一个学生在一周内而不是下一周在场，那么当月的学生会得到 1（假设它只出现一次），缺席的学生会得到 0。我尝试了 count() 和 joins 的多种变体，但无济于事。任何帮助将不胜感激。以下是截断的小提琴：

http://www.sqlfiddle.com/#!9/36a6e0

这是我想要实现的示例：

Name | CurrWeek | LastWeek

Paula | 0 | 2

Answer 1

试试这个

两张桌子

Select name, max(current_week) current_week, max(last_week) as last_week
    From (
    Select name, count(1) as current_week, 0 as last_week from currentWeek group by name
    union all
    Select name, 0 as current_week, count(1) as last_week from lastWeek group by name
    ) x
    group by name

3张桌子

Select name, max(current_week) current_week, max(last_week) as last_week, max(third_week) as third_week
    From (
    Select name, count(1) as current_week, 0 as last_week, 0 as thrid_week from currentWeek group by name
    union all
    Select name, 0 as current_week, count(1) as last_week, 0 as thrid_week from lastWeek group by name
    union all
    Select name, 0 as current_week, 0 as last_week, count(1) as thrid_week from thirdWeek group by name
    ) x
    group by name

Answer 2

你需要加入和计数，合并两个结果集需要联合

select T1.name,T1.currentwk,T2.lasttwk from 
    (
    select name,count(id) as currentwk from currentWeek

    group by name
    ) as T1

     left  join 
     (

     select name,count(id) as lasttwk from lastWeek

    group by name
       ) as T2
       on T1.name=T2.name

     union 
     select T2.name,T1.currentwk,T2.lasttwk from 
    (
    select name,count(id) as currentwk from currentWeek

    group by name
    ) as T1

     right  join 
     (

     select name,count(id) as lasttwk from lastWeek

    group by name
       ) as T2
       on T1.name=T2.name

http://www.sqlfiddle.com/#!9/36a6e0/25