SQL ORDER BY with CASE with UNION ALL

运行PostgreSQL(7.4和8.x),我认为这是工作,但现在我收到错误.

我可以单独运行查询,它的工作正常,但如果我UNION或UNION ALL它会引发错误.

这个错误输出：(警告：pg_query()：查询失败：错误：列“Field1”不存在… ORDER BY CASE“Field1”W …)

SELECT "Field1" AS field_1,"Field2" AS field_2,"Field3" AS field_3,"Field4" AS field_4
FROM "TableName" 
WHERE condition
AND other_condition
UNION ALL
SELECT "Field1" AS field_1,"Field4" AS field_4
FROM "TableName" 
WHERE yet_another_condition
AND yet_another_other_condition
ORDER BY CASE "Field1"
    WHEN 'A' THEN 1
    WHEN 'B' THEN 2
    WHEN 'C' THEN 3
    ELSE 4
END

这样做：

SELECT "Field1" AS field_1,"Field4" AS field_4
FROM "TableName" 
WHERE yet_another_condition
AND yet_another_other_condition
ORDER BY CASE "Field1"
    WHEN 'A' THEN 1
    WHEN 'B' THEN 2
    WHEN 'C' THEN 3
    ELSE 4
END

这也是如此：

SELECT "Field1" AS field_1,"Field4" AS field_4
FROM "TableName" 
WHERE condition
AND other_condition
ORDER BY CASE "Field1"
    WHEN 'A' THEN 1
    WHEN 'B' THEN 2
    WHEN 'C' THEN 3
    ELSE 4
END

如果我离开ORDER BY,并且使用UNION或UNION ALL,它也可以工作.

有任何想法吗？

解决方法

SELECT * FROM (
  SELECT "Field1" AS field_1,"Field4" AS field_4
  FROM "TableName" 
  WHERE condition
  AND other_condition
  UNION ALL
  SELECT "Field1" AS field_1,"Field4" AS field_4
  FROM "TableName" 
  WHERE yet_another_condition
  AND yet_another_other_condition
) As A
ORDER BY CASE field_1
    WHEN 'A' THEN 1
    WHEN 'B' THEN 2
    WHEN 'C' THEN 3
    ELSE 4
END

或者更好地使用ORDER BY中的别名,因为它在UNION的结尾传递：

SELECT "Field1" AS field_1,"Field4" AS field_4
  FROM "TableName" 
  WHERE yet_another_condition
  AND yet_another_other_condition
  ORDER BY CASE field_1
    WHEN 'A' THEN 1
    WHEN 'B' THEN 2
    WHEN 'C' THEN 3
    ELSE 4
  END

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