sql - 不使用 USING 加入子查询

Question

我有这样的查询

SELECT DISTINCT
    [fldID],
    [fldValue]
            FROM
                (
                    (
                        SELECT
                            alias1.[fldID],
                            alias1.[fldValue]
                        FROM someT as alias1
                            ....
                    )
                ) AS subQuery_1
            INNER JOIN
            (
                SELECT
                    alias1.[fldID],
                    alias1.[fldValue]
                FROM someT as alias1
                    ...
            ) AS subQuery_2 USING( fldID, fldValue) 

它在 MySQL 中运行良好，但 SQL Server 不支持 USING。所以我必须像这样使用 JOIN ：

ON [subQuery_1].[fldID] = [subQuery_2].[fldID] 
AND [subQuery_1].[fldValue] = [subQuery_2].[fldValue]

但是这个查询会导致错误：

Ambiguous column name fldID 
Ambiguous column name fldValue

那么，如何在 SQL Server 中实现这种 JOIN 呢？

Answer 1

您只需要指定从哪个子查询中获取这些列（在您加入两列时，您选择哪一个并不重要）

SELECT DISTINCT
subQuery_1.[fldID],
subQuery_1.[fldValue]
        FROM
            (
                (
                    SELECT
                        alias1.[fldID],
                        alias1.[fldValue]
                    FROM someT as alias1
                        ....
                )
            ) AS subQuery_1
        INNER JOIN
        (
            SELECT
                alias1.[fldID],
                alias1.[fldValue]
            FROM someT as alias1
                ...
        ) AS subQuery_2 
 ON [subQuery_1].[fldID] = [subQuery_2].[fldID] 
 AND [subQuery_1].[fldValue] = [subQuery_2].[fldValue]

Answer 2

在您的查询中，您没有在最终选择中添加表别名。您需要指定来自哪个表的列，如下所示：

SELECT DISTINCT
    subQuery_1.[fldID],
    subQuery_1.[fldValue]
            FROM
                (
                    (
                        SELECT
                            alias1.[fldID],
                            alias1.[fldValue]
                        FROM someT as alias1
                            ....
                    )
                ) AS subQuery_1
            INNER JOIN
            (
                SELECT
                    alias1.[fldID],
                    alias1.[fldValue]
                FROM someT as alias1
                    ...
            ) AS subQuery_2 
            on [subQuery_1].[fldID] = [subQuery_2].[fldID] 
AND [subQuery_1].[fldValue] = [subQuery_2].[fldValue]