sql - 如何按第一列区分

Question

Select DISTINCT wpg.ID as id1,wr.ID as id2
FROM Table1 wpg
inner join Table2 wp ON wp.WpgId = wpg.ID
inner join Table3 wr ON wr.WpId = wp.ID

我需要 wpg.Id distinct 怎么做？

我需要：

1 2

2 3

1 4

得到：

1 2

2 3

Answer 1

答案取决于您想对第二列做什么。我假设你想要最小值：

select
    wpg.ID as id1,
    min(wr.ID) as id2
from
    Table1 wpg
    inner join Table2 wp on wp.WpgId = wpg.ID
    inner join Table3 wr on wr.WpId = wp.ID
group by
    wpg.ID

Answer 2

select wpg.ID, min(wr.ID)
FROM Table1 wpg 
inner join Table2 wp ON wp.WpgId = wpg.ID 
inner join Table3 wr ON wr.WpId = wp.ID 
group by wpg.ID