Question

我有3个订单表

Orders1：

OrderNumber, TransactionID, TrackingNumber

Orders2：

OrderNumber, TransactionID, TrackingNumber

Orders3：

OrderNumber, TransactionID, TrackingNumber

我显示了未完成的订单总数，因此我需要从TrackingNumber = ''

的表格中进行选择

Answer 1

您需要使用UNION：

SELECT * FROM orders1 WHERE TrackingNumber = ''
UNION
SELECT * FROM orders2 WHERE TrackingNumber = ''
UNION
SELECT * FROM orders3 WHERE TrackingNumber = ''

Answer 2

这是一种使用子查询的方法。

SELECT
  (SELECT COUNT(*) FROM Orders1 WHERE TrackingNumber='')
  + (SELECT COUNT(*) FROM Orders2 WHERE TrackingNumber='')
  + (SELECT COUNT(*) FROM Orders3 WHERE TrackingNumber='')
AS `total`
FROM DUAL;

告诉我它是否按预期工作：）

值得一提的是，您应该将TrackingNumber字段编入索引。

Answer 3

试试这个：

select 
    sum(a.subtotal )
from
    (select count(*) as subtotal from Orders1 where TrackingNumber=''
    union all
    select count(*) as subtotal from Orders2 where TrackingNumber=''
    union all
    select count(*) as subtotal from Orders3 where TrackingNumber=''
   ) a

MySQL：从多个表中选择数据

3 个答案: