Question

I’ve got a settings table constructed with ‘category’ determining different products, ‘varname’ being the variable name, and ‘info’ being the value of the setting.

so, for instance,

select top 6 category, varname, info 
from settings_table 
where NODE_NAME='HTT-COMM-A' 
  and section='Module Settings' 
  and category in  ('ProductA', 'ProductB') 
order by varname

results in :

 category   varname             info  
 ProductB   WEB_ACCESS_ALLOW    NO  
 ProductA   WEB_ACCESS_ALLOW    NO  
 ProductB   WEB_ACCESS_BLOCK    YES  
 ProductA   WEB_ACCESS_BLOCK    YES  
 ProductB   WEB_ACCOUNT_DETAIL  NO  
 ProductA   WEB_ACCOUNT_DETAIL  YES  

I’d like to generate a simple list of differences between the values when category=’ProductA’ and ‘ProductB’. I can think of a number of ways to do this with a temporary table, or by a number of subselects (for instance, this painful one) :

select a.category, a.varname, a.info , b.category, b.info 
from (select category, varname, info, description
      from settings_table 
      where category = 'ProductA') as a,
     (select category, varname,info, description 
      from settings_table 
      where category = 'ProductB') as b 
where a.varname=b.varname and a.info != b.info

but the above method (at least) fails when there’s a varname in b that isn’t in a. (Any solutions should fix this problem, any differences in varnames between a and b should be represented as well.)

This isn’t a hard problem to solve in a kludgy way, but I wonder if there’s a ‘right way’ to do this elegantly, without the horrid sub-selects or without the caveats above.

This is more SQL agnostic, but this particular table is in a MSSQL server.

Thanks,
Rk

Answer 1

If you only cared about the varname and info values, you could do something like:

Select varname, info
From @Data As T
Except  (
        Select varname, info
        From @Data As T1
        Where category = 'ProductA'
        Intersect
        Select varname, info
        From @Data As T2
        Where category = 'ProductB'
        )

If you wanted other columns from the source table, then you can do something like:

Select T.*
From settings_table As T
    Left Join   (
                Select T1.varname, T1.info
                From settings_table As T1
                Where T1.category = 'ProductA'
                    And T1.NODE_NAME='HTT-COMM-A' 
                    And T1.section='Module Settings'
                Intersect
                Select T2.varname, T2.info
                From settings_table As T2
                Where T1.category = 'ProductB'
                    And T1.NODE_NAME='HTT-COMM-A' 
                    And T1.section='Module Settings'
                ) As Z
        On Z.varname = T.varname
            And Z.info = T.info
Where Z.varname Is Null
    And T.NODE_NAME='HTT-COMM-A' 
    And T.section='Module Settings'

Yet a third way would be to simply use an EXISTS predicate:

Select T.*
From settings_table As T
Where T.NODE_NAME='HTT-COMM-A' 
    And T.section='Module Settings'
    And Not Exists  (
                    Select 1
                    From settings_table As T2
                    Where T2.category In('ProductA','ProductB')
                        And T2.varname = T.varname
                        And T2.info = T.info
                    Group By T2.varname, T2.info
                    Having Count(*) = 2
                    )