SQL服务器，差异两个表并混合在一起

Question

例如，我有两个表：tbMetals和tbSells

tbMetals

mId - name   - cost
1   - Iron   - 100
2   - Steel  - 200
3   - Copper - 300
4   - Zinc   - 150

tbSells

CustomerId - mId - SellDate - weight
100        - 1   - 2017/1/1 - 1.2
100        - 2   - 2017/1/2 - 3.5
111        - 1   - 2017/3/3 - 2.1

我需要ClientId = 100的这个输出

mId - SellDate - weight
1   - 2017/1/1 - 1.2
2   - 2017/1/2 - 3.5
3   - NULL     - NULL
4   - NULL     - NULL

Answer 1

这是一个简单的左连接。

select
    m.mId
    ,s.SellDate
    ,s.weight
from
    tbMetals m
left join
    tbSells s on
    s.mId = m.mId
    and s.ClientId = 100   --optional, if you really want it.