我希望你能带我来这里。我正在开发一个 PMS 系统，我想运行一个简单的 SELECT 语句，根据客户的包裹已到达和交易类型来获取他们的密码列表。 “transferConfirmation”表已经具有客户 ID 和密码，并为每个实例显示一行，但由于某种原因，当我使用以下查询时:
SELECT `tc`.`transferID` AS `transferID`,
`c`.`firstName` AS `firstName`,
`c`.`lastName` AS `lastName`,
`tc`.`secretCode` AS `secretCode`,
'Purchase Order' AS `transactionType`
FROM (((((`db`.`transferconfirmation` `tc`
JOIN `db`.`customer` `c` on((`tc`.`customerID` = `c`.`customerID`)))
JOIN `db`.`transfer` `t` on((`t`.`transferID` = `tc`.`transferID`)))
JOIN `db`.`transferentry` `te` on((`t`.`transferID` = `te`.`transferID`)))
JOIN `db`.`purchaseorder` `po` on((`te`.`referenceID` = `po`.`purchaseOrderID`)))
JOIN `db`.`purchaseorderentry` `poe` on(((`po`.`purchaseOrderID` = `poe`.`purchaseOrderID`)
AND (`te`.`referenceEntryID` = `poe`.`purchaseOrderEntryID`))))
WHERE (`poe`.`collectionStatus` = 0)
UNION ALL
SELECT `tc`.`transferID` AS `transferID`,
`c`.`firstName` AS `firstName`,
`c`.`lastName` AS `lastName`,
`tc`.`secretCode` AS `secretCode`,
'Shipping Order' AS `transactionType`
FROM (((((`db`.`transferconfirmation` `tc`
JOIN `db`.`customer` `c` on((`tc`.`customerID` = `c`.`customerID`)))
JOIN `db`.`transfer` `t` on((`t`.`transferID` = `tc`.`transferID`)))
JOIN `db`.`transferentry` `te` on((`t`.`transferID` = `te`.`transferID`)))
JOIN `db`.`shippingorder` `so` on((`te`.`referenceID` = `so`.`shippingOrderID`)))
JOIN `db`.`shippingorderentry` `soe` on(((`so`.`shippingOrderID` = `soe`.`shippingOrderID`)
AND (`te`.`referenceEntryID` = `soe`.`shippingOrderEntryID`))))
WHERE (`soe`.`collectionstatus` = 0)
我不断得到重复数据的结果，唯一的区别在于交易。我想我的问题是，如果已选择一次密码，如何防止任何其他行显示相同的代码。
最佳答案
使用UNION运算符。 UNION 运算符将从每个查询中删除重复记录(UNION ALL 将保留它们)。
SELECT transferID, firstName, lastName, secretCode,
'Purchase Order' AS transactionType
FROM ...
UNION
SELECT transferID, firstName, lastName, secretCode,
'Purchase Order' AS transactionType
FROM ...
关于mysql - 我的 MySQL 查询 (UNION) 有什么问题？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/34918310/