Question

Situation: A PHP application with multiple installable modules creates a new table in database for each, in the style of mod_A, mod_B, mod_C etc. Each has the column section_id.

Now, I am looking for all entries for a specific section_id, and I’m hoping there’s another way besides ‘Select * from mod_a, mod_b, mod_c … mod_xyzzy where section_id=value’… or even worse, using a separate query for each module.

Answer 1

If the tables are changing over time, you can inline code gen your solution in an SP (pseudo code – you’ll have to fill in):

SET @sql = ''  DECLARE CURSOR FOR SELECT t.[name] AS TABLE_NAME FROM sys.tables t WHERE t.[name] LIKE 'SOME_PATTERN_TO_IDENTIFY_THE_TABLES' 

— or this

DECLARE CURSOR FOR SELECT t.[name] AS TABLE_NAME FROM TABLE_OF_TABLES_TO_SEACRH t  START LOOP  IF @sql <> '' SET @sql = @sql + 'UNION ALL ' SET @sql = 'SELECT * FROM [' + @TABLE_NAME + '] WHERE section_id=value '  END LOOP  EXEC(@sql) 

I’ve used this technique occasionally, when there just isn’t any obvious way to make it future-proof without dynamic SQL.

Note: In your loop, you can use the COALESCE/NULL propagation trick and leave the string as NULL before the loop, but it’s not as clear if you are unfamiliar with the idiom:

SET @sql = COALESCE(@sql + ' UNION ALL ', '')     + 'SELECT * FROM [' + @TABLE_NAME + '] WHERE section_id=value '