Question

I am a bit puzzled about the best way to construct a stored procedure that returns a SELECT-statement based on table row values in another table.

The problem might be best described as this:

Table Name: reportValues
--------------------------------------------
ID       name       date        region
--------------------------------------------
1        Stefan     2010-01-01  UK
2        David      2010-01-05  SE
3        Anna       2010-01-12  NO
4        Marie      2010-01-15  NO


Table Name: reportParameters
-------------------------------
ID       column     queryValue 
-------------------------------
1        ID       
2        name     
3        date       
4        region     

Based on what the user enters in the queryValue column in the reportParameters table, I want to construct a stored procedure what executes a SELECT-statement such as this:

SELECT * FROM reportValues WHERE region = 'NO' 

If the user had entered the following values:

Table Name: reportParameters
-------------------------------
ID       column     queryValue 
-------------------------------
1        ID       
2        name       
3        date       
4        region     NO

But it might as well be:

SELECT * FROM reportValues WHERE region = 'NO' AND name = 'Anna'

If the user had entered:

Table Name: reportParameters
-------------------------------
ID       column     queryValue 
-------------------------------
1        ID       
2        name       Anna
3        date       
4        region     NO

My initial thought of doing it was to make a loop that constructs the SELECT-statement into a string variable and executes it. But it got to be a more elegant solution?

Answer 1

I’m not sure there is, if the queries have a small, known, set of fields, then you could list them all in the where accompanied a selector:

(IF NOT NULL reportParameters.field AND reportParameters.field = reportValues.field)

There is no short-circuit evaluation, but it might still have the desired effect. Otherwise it is down to dynamic SQL and EXEC().