Question

我有这段代码：

SELECT A.UNITCODE, B.FORMATIONCODE, C.UPPERFORMATIONCODE, D.UPPERFORMATIONCODE 
FROM UNIT AS A.UNITCODE 
INNER JOIN FORMATION AS B.FORMATIONCODE 
INNER JOIN UPPERFORMATION_UNIT AS C.UPPERFORMATION 
INNER JOIN UPPERFORMATION AS D.UPPERFORMATIONCODE 
WHERE UNITCODE='7000007'

你们能帮助我如何用指定的列加入4个表吗？

Answer 1

确定所有3个相关表具有相同的UNIT_ID以便与表UNIT

连接

  SELECT 
        A.UNITCODE
      , B.FORMATIONCODE
      , C.UPPERFORMATIONCODE
      , D.UPPERFORMATIONCODE 
  FROM UNIT AS A 
  INNER JOIN FORMATION AS B ON B.FORMATIONCODE  = A.UNIT_ID
  INNER JOIN UPPERFORMATION_UNIT AS C. C.UPPERFORMATION  = A.UNIT_ID
  INNER JOIN UPPERFORMATION AS D D.UPPERFORMATIONCODE  = A.UNIT_ID
  WHERE UNITCODE='7000007'

Answer 2

您似乎在混淆表别名和链接列。

这是如何在查询中为表提供别名以增强可读性：

INNER JOIN formation AS f

AS是可选的。大多数情况下它都被忽略了。

这是如何加入：

FROM unit AS u
INNER JOIN upperformation_unit AS ufu ON ufu.unitcode = u.unitcode

好吧，我当然不知道连接表格的列，更不用说他们的名字了。但我认为查询必须或多或少看起来像这样：

SELECT 
  u.unitcode,
  f.formationcode,
  uf.upperformationcode,
  ufu.upperformationcode 
FROM unit u
JOIN upperformation_unit ufu ON ufu.unitcode = u.unitcode
JOIN upperformation uf ON uf.upperformationcode = ufu.upperformationcode
JOIN formation f ON f.formationcode uf.formationcode
WHERE u.unitcode = 7000007;

使用指定列加入4个表

2 个答案: