mysql - 如何在mysql中基于ncarpk连接三个表

Question

我想检查 tour_customer、tour_provider、reservation 中的 ncarpk，如果任何表有 ncarpk = 7 的记录，然后显示结果。

select *
from tour_customer
    Left Outer join tour_provider on tour_provider.nCarPk = '7'
    Left Outer join reservation on reservation.nCarPk = '7' 
where tour_customer.ncarpk = '7'

Answer 1

我会尝试

select *
from tour_customer
Left Outer join tour_provider on tour_provider.nCarPk =customer.ncarpk     
Left Outer join reservation on reservation.nCarPk = customer.ncarpk  
where tour_customer.ncarpk = '7'

这是进行连接的常规方法，您说出要在哪个字段上进行连接，然后添加 where 子句。