Question

运行PostgreSQL（7.4和8.x），我认为这有效，但现在我遇到了错误。

我可以单独运行查询，但它运行正常，但是如果我UNION或UNION ALL它会抛出错误。

此错误输出:(警告：pg_query（）：查询失败：错误：列“Field1”不存在...按案例排序“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, "Field2" AS field_2,
"Field3" AS field_3, "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

这有效：

SELECT "Field1" AS field_1, "Field2" AS field_2,
"Field3" AS field_3, "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

这也有效：

SELECT "Field1" AS field_1, "Field2" AS field_2,
"Field3" AS field_3, "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

如果我不使用ORDER BY并且只使用UNION或UNION ALL，它也会起作用。

任何想法？

Answer 1

将所有内容放入另一个SELECT：

SELECT * FROM (
  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, "Field2" AS field_2,
  "Field3" AS field_3, "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

或者更好的是，使用ORDER BY中的别名，因为它在UNION的末尾传递：

  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, "Field2" AS field_2,
  "Field3" AS field_3, "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

Answer 2

第一个不起作用，因为你应该

ORDER BY CASE field_1

"Field1"仅在单个子查询中可用，并且在使用公共别名创建UNION后，您不能再将该列称为"Field1"。

带有UNION ALL的CASE的SQL ORDER BY

2 个答案: