How to dynamically generate table column definitions in SQL Server 2008 function

Question

IN SQL Server 2008 I have a situation where I need to return a dynamically generated table, and the columns are also dynamically generated.

Everything in this was generated by queries, as I started with one id, then I get the column names and types, which is why the casting.

Following is the final query, that will return the table I want, in one situation, but this similar query can be used to return several tables.

This is currently implemented in C# but I expect it should be doable in a stored procedure or function, but, I am not certain how I can make several queries to build up this query, to then return the table.

Thank you.

SELECT ResultID, ResultName, ResultDescription, 
CAST([233] AS Real) as [ResultColA], 
CAST([234] AS Int) as [ResultColB], 
CAST([236] AS NVarChar) as [ResultColC], 
CAST([237] AS Int) as [ResultColD]
FROM (
    SELECT st.*, avt.ResultID as avtID, avt.SomeAttrID, avt.Value 
    FROM Result_AV avt 
    JOIN Result st ON avt.ResultID = st.ResultID) as p 
    PIVOT ( 
     MAX(Value) FOR AttributeID IN ([233], [234], [236], [237])) as pvt

Update: If I have a table that has manufacturer of vehicles, and I want all the attributes of cars made by GM. I would look up the information for cars, use that to get all the manufacturers of cars, which would be GM, then I want to get the information of all the cars made by GM, but, since the information has been dynamically generated the columns are different. That is the place I am at, needing to dynamically generate this table. I am curious if I can perhaps just call out to a webservice, get the dynamically generated query and then have the stored procedure or function execute that query.

Update 2: The next step after I get this table is that I will need to add up all the options on the car (in this case), to determine the actual price of the car. That is why it needs to be in a tabular format. At this point I am looking at cars made by GM, but I could do another query on boats made by SeaRay and the query should work the same even though the table columns on the boats are different than the cars were.

Answer 1

You can do this with dynamic SQL. You need to build your two lists appropriately with a query and/or metadata and then insert them into the SQL:

DECLARE @template AS varchar(MAX)

SET @template = '
SELECT ResultID, ResultName, ResultDescription
{@SELECT_COLUMN_LIST}
FROM (
    SELECT st.*, avt.ResultID as avtID, avt.SomeAttrID, avt.Value 
    FROM Result_AV avt 
    JOIN Result st ON avt.ResultID = st.ResultID) as p 
    PIVOT ( 
        MAX(Value) FOR AttributeID IN ({@PIVOT_COLUMN_LIST})) as pvt'

DECLARE @sql AS varchar(MAX)

SET @sql = REPLACE(REPLACE(@template, '{@SELECT_COLUMN_LIST}', @SELECT_COLUMN_LIST), '{@PIVOT_COLUMN_LIST}', @PIVOT_COLUMN_LIST)

EXEC (@sql)

To populate the @SELECT_COLUMN_LIST and @PIVOT_COLUMN_LIST, you've got several options, but something like this avoids any need for a cursor or awkward string operations:

SELECT @PIVOT_COLUMN_LIST = COALESCE(@PIVOT_COLUMN_LIST, '') + ',' + QUOTENAME(value)
FROM (SELECT DISTINCT value FROM table)

Obviously for @SELECT_COLUMN_LIST you need to combine this information with some metadata.

I have done things like that for ease of maintenance because PIVOT and UNPIVOT do not allow lists to be dynamic SQL (because they result in a schema change on the output table). For for client-side report-style or listbox usage where the columns aren't interpreted, it doesn't matter.