Question

我很难两次加入相同的表格，因此返回的结果完全不正确。

下面的查询工作得很好。但是，我想更改它，以便我可以使用Requirement Type列中返回的值返回Requirement Traced To的额外列。

SELECT    R.RQ_REQ_ID      as "Requirement Traced From",
          R.RQ_REQ_NAME    as "Requirement Name",
          RTY.TPR_NAME     as "Requirement Type",
          RTR.RT_TO_REQ_ID as "Requirement Traced To"
FROM      REQ R
LEFT JOIN REQ_TRACE RTR
ON        R.RQ_REQ_ID = RTR.RT_FROM_REQ_ID, Req_Type RTY
WHERE     R.RQ_TYPE_ID = RTY.TPR_TYPE_ID
AND       RTY.TPR_NAME in ('TOM', 'Business Process Map', 'Work Instruction', 'Functional', 'Customer Journey', 'Business')
ORDER BY  1

当我第二次使用不同的别名添加REQ和REQ_TYPE表时，我会返回数百行，而不是我期待的28行。

任何帮助将不胜感激。

Answer 1

从不在FROM子句中使用逗号。始终使用明确的JOIN语法。

您需要添加以下附加联接：

SELECT R.RQ_REQ_ID      as "Requirement Traced From",
       R.RQ_REQ_NAME    as "Requirement Name",
       RTY.TPR_NAME     as "Requirement Type",
       RTR.RT_TO_REQ_ID as "Requirement Traced To",
       RTY2.TPR_NAME    as "Requirement Type To",
FROM REQ R LEFT JOIN
     REQ_TRACE RTR
     ON R.RQ_REQ_ID = RTR.RT_FROM_REQ_ID LEFT JOIN
     Req_Type RTY
     ON R.RQ_TYPE_ID = RTY.TPR_TYPE_ID LEFT JOIN
     REQ R R2
     ON R2.RQ_REQ_ID = RTR.RT_TO_REQ_ID LEFT JOIN
     Req_Type RTY2
     ON RTY2.TPR_TYPE_ID = R2.RQ_TYPE_ID
WHERE RTY.TPR_NAME in ('TOM', 'Business Process Map', 'Work Instruction', 'Functional', 'Customer Journey', 'Business')
ORDER BY 1;

Answer 2

使用逗号后，您需要使用两个join而不是在连接条件后写表名：

SELECT    R.RQ_REQ_ID      as "Requirement Traced From",
      R.RQ_REQ_NAME    as "Requirement Name",
      RTY.TPR_NAME     as "Requirement Type",
      RTR.RT_TO_REQ_ID as "Requirement Traced To"
FROM      REQ R
LEFT JOIN REQ_TRACE RTR
ON        R.RQ_REQ_ID = RTR.RT_FROM_REQ_ID
LEFT JOIN Req_Type RTY
ON R.RQ_TYPE_ID = RTY.TPR_TYPE_ID
  and RTY.TPR_NAME in ('TOM', 'Business Process Map', 'Work Instruction', 'Functional', 'Customer Journey', 'Business')
ORDER BY  1

SQL查询 - 多个联接

2 个答案: