左外连接到生成的表？

Question

我的方针完全错误吗？ 我想对从 2 个表生成的查询进行左外连接，但我不断收到错误。我需要不同的方法吗？

t1:

ID, Surname,Firstname

t2:

ID,JobNo,Confirmed

我有以下查询：

SELECT JobNo AS N, StaffID AS P, Confirmed as C, 
       FirstName AS F,Surname AS S 
FROM gigs_players, Players 
WHERE t1.StaffID=t2.StaffID AND JobNo="2" 
      AND (`Confirmed` IS NULL OR Confirmed ='Y' ) 
ORDER BY Instrument,Surname

我想添加：

LEFT OUTER JOIN contacted (ON t1.StaffID=contact.ID AND t2.JobNo=contact.JobNo)"

我可以对从 2 个表生成的查询执行左外连接吗？

Answer 1

为了在要添加的左外连接中使用 t1 和 t2，您需要将它们与第一个表连接，您不能直接在左外连接，如下所示：

SELECT JobNo AS N, StaffID AS P, Confirmed as C, 
   FirstName AS F,Surname AS S 
FROM gigs_players, Players
Inner join t1 on ...
Inner join t2 on ...
LEFT OUTER JOIN contacted c 
     on t1.StaffID=c.ID AND t2.JobNo = c.JobNo
WHERE t1.StaffID=t2.StaffID AND JobNo="2" 
    AND (`Confirmed` IS NULL OR Confirmed ='Y' ) 
ORDER BY Instrument,Surname

因此，根据表的结构，定义与其他表的 t1 和 t2 的两个连接的条件。

Answer 2

以下是子查询的左连接示例。这可能就是您正在寻找的。

select 
parts.id, 
min(inv2.id) as nextFIFOitemid 
from test.parts 
left join 
( select 
  inventory.id, 
  coalesce(parts.id, 1) as partid 
  from test.inventory 
  left join test.parts 
  on (parts.id = inventory.partid) 
) inv2 
on (parts.id = inv2.partid) 
group by parts.id;