How to work around SQL Server's “The maximum number of tables in a query (260) was exceeded.”

Question

i have a query that contains a series of 21 UNIONs, e.g.:

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

The query runs fine when run alone. But when the query is run through the containing view:

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.

i've tried splitting up my USGovFedExpentiures view into smaller chunks:

CREATE VIEW dbo.USGovCurrencyOnHandBreakdown AS

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

With USGovCurrencyOnHandBreakdown_Additions and USGovCurrencyOnHandBreakdown_Subtractions each containing roughly half the queries:

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

But selecting from the "parent" view still fails:

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.

How can i work around the 256 table limit?

See also

• FIX: A Transact-SQL query that uses views may fail unexpectedly in SQL Server 2000 SP3
• MSDN: Maximum Capacity Specifications for SQL Server

Answer 1

A colleague came up with a great answer. Use a function to return a table variable; insert the results into the table variable bit by bit:

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

with the view now calling the UDF:

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

As far as any clients know the view is unchanged. (Except now it works!)

Answer 2

You could store the subqueries into temp tables, e.g. the USGovCurrencyOnHandBreakdown_Additions and USGovCurrencyOnHandBreakdown_Subtractions that you mentioned, and than selecting from those temp tables instead of views.

Of course, the transactions could be an issue because of the dirty reads, I don't know if that's a concern in this case...