Question

我的查询包含一系列21 UNIONs，例如：

CREATE VIEW dbo.USGovCurrencyOnHandBreakdown AS

   SELECT ... FROM a
   UNION ALL
   SELECT ... FROM b
   UNION ALL
   SELECT ... FROM c
   UNION ALL
   SELECT ... FROM d
   ...
   UNION ALL
   SELECT ... FROM u

单独运行时查询运行正常。但是当查询通过包含视图运行时：

SELECT * FROM USGovCurrencyOnHandBreakdown 

Msg 4414, Level 16, State 1, Line 1
Could not allocate ancillary table for view or function resolution. The maximum number of tables in a query (260) was exceeded.

我尝试将USGovFedExpentiures视图拆分为较小的块：

CREATE VIEW dbo.USGovCurrencyOnHandBreakdown AS

   SELECT x FROM TreasuryAuditResults
   UNION ALL
   SELECT x FROM USGovCurrencyOnHandBreakdown_Additions
   UNION ALL
   SELECT x FROM USGovCurrencyOnHandBreakdown_Subtractions

USGovCurrencyOnHandBreakdown_Additions和USGovCurrencyOnHandBreakdown_Subtractions分别包含大约一半的查询：

CREATE VIEW USGovCurrencyOnHandBreakdown_Additions AS
   SELECT ... FROM b
   UNION ALL
   SELECT ... FROM c
   ...
   SELECT ... FROM k

CREATE VIEW USGovCurrencyOnHandBreakdown_Subtractions AS
   SELECT ... FROM l
   UNION ALL
   SELECT ... FROM m
   ...
   SELECT ... FROM u

但是从“父”视图中选择仍然失败：

SELECT * FROM USGovCurrencyOnHandBreakdown

Msg 4414, Level 16, State 1, Line 1
Could not allocate ancillary table for view or function resolution. The maximum number of tables in a query (260) was exceeded.

我如何解决256个表限制？

另见

Answer 1

一位同事想出了一个很好的答案。使用函数返回表变量;将结果逐位插入表变量：

CREATE VIEW dbo.USGovCurrencyOnHandBreakdown AS
    SELECT * FROM fn_USGovCurrencyOnHandBreakdown()

现在调用UDF视图：

CREATE FUNCTION dbo.fn_USGovCurrencyOnHandBreakdown()
    RETURNS @Results TABLE
    (
        Total money, 
        ...
    )

    INSERT INTO @Results SELECT ... FROM a
    INSERT INTO @Results SELECT ... FROM b
    INSERT INTO @Results SELECT ... FROM c
    INSERT INTO @Results SELECT ... FROM d
      ...
    INSERT INTO @Results SELECT ... FROM u

    RETURN 
END

任何客户都知道view没有变化。（现在它除外了！）

Answer 2

您可以将子查询存储到临时表中，例如您提到的USGovCurrencyOnHandBreakdown_Additions和USGovCurrencyOnHandBreakdown_Subtractions，而不是从那些临时表而不是视图中进行选择。

当然，交易可能是一个问题，因为脏读，我不知道在这种情况下这是否是一个问题......

如何解决SQL Server“超出了查询中的最大表数（260）。”

另见

2 个答案: