mysql - 带有左连接和并集的 SELECT

Question

我有一个查询，该查询返回特定员工类次的发票

SELECT
i.dateTime,i.amount,i.totalProfit,i.shiftID,
i_o.itemID,i_o.quantity,
item.name itemName,
p.full_name

from invoice i 

LEFT JOIN 
inv_order i_o on i_o.invID=i.invID

LEFT JOIN 
`item-service` item on item.itemID = i_o.itemID


LEFT JOIN person p on 
p.PID=i.personID

where i.shiftID =97

但是，我需要从员工表中获取员工姓名，而我只有 shiftID。

SELECT
i.dateTime,i.type,i.amount,i.totalProfit,i.shiftID,i_o.itemID,i_o.quantity,item.name itemName,p.full_name

from invoice i 

LEFT JOIN 
inv_order i_o on i_o.invID=i.invID

LEFT JOIN 
`item-service` item on item.itemID = i_o.itemID


LEFT JOIN person p on 
p.PID=i.personID

where i.shiftID =97

UNION

SELECT e.name from employee e

left join shift s on s.empID = e.empID

where s.shiftID =97

mysql返回这个错误

使用的 SELECT 语句具有不同的列数

Answer 1

错误消息对于问题非常清楚:您的第一个查询返回 8 列数据，而第二个查询仅返回 1 列，因此您无法对它们进行UNION。看来您可能只想通过 shift 表JOIN employee 表，例如

SELECT i.dateTime
      ,i.type
      ,i.amount
      ,i.totalProfit
      ,i.shiftID
      ,i_o.itemID
      ,i_o.quantity
      ,item.name AS itemName
      ,p.full_name
      ,e.name
FROM invoice i 
LEFT JOIN inv_order i_o ON i_o.invID=i.invID
LEFT JOIN `item-service` item ON item.itemID = i_o.itemID
LEFT JOIN person p ON p.PID=i.personID
LEFT JOIN shift s ON s.shiftID = i.shiftID
LEFT JOIN employee e ON e.empID = s.empID
WHERE i.shiftID = 97