Question

I am writing a query in SQL to be used for SSRS 2005 which is

select t1.Category, t2.condition,'1' as hasCondition from t1
left outer join t2 on t1.ID = t2.ID
left outer join t3 on t2.cID = t3.cID
where t3.clientID = 6 

union

select t1.Category, t2.condition, '0' as hasCondition from t1
left outer join t2 on t1.ID = t2.ID

and it returns the data as:

  Category            Condition            hasCondition

 Behavioural       Tourette's Syndrome         0
 Communications    Impaired Speech             0
 Dexterity         Osteoarthritus              0
 Dexterity         Osteoporosis                0
 Dexterity         Other Dexterity             0
 Dexterity         Rheumatoid Arthritus        0
 Emotional         Bipolar Disorder            0
 Emotional         Clinical Depression        0
 Emotional         Depression                 0
 Emotional         Depression                 1
 Emotional         Gulf War Syndrome          0
 Emotional         Gulf War Syndrome          1

Now I want to select only one record from duplicates rows/results for example:
Category-Emotional, condition-Depression which hasCondition ‘1’ or ‘true’

I hope I made it clear using the example.
Please help me.

Thanks.

Answer 1

It’s not 100% clear what you want, but I think you’re just looking for the MAX() of the final field…

SELECT
  category, condition, MAX(has_condition) AS hasCondition
FROM
(
  select t1.Category, t2.condition,'1' as hasCondition from t1
  left outer join t2 on t1.ID = t2.ID
  left outer join t3 on t2.cID = t3.cID
  where t3.clientID = 6 

  union

  select t1.Category, t2.condition, '0' as hasCondition from t1
  left outer join t2 on t1.ID = t2.ID
)
  AS data
GROUP BY
  category, condition

If you wanted to simplify that whole query…

  select
    t1.Category,
    t2.condition,
    MAX(CASE WHEN t3.clientID = 6 THEN 1 ELSE 0 END) as hasCondition
  from
    t1
  left outer join
    t2
      on  t2.ID = t1.ID
  left outer join
    t3
      on  t3.cID = t2.cID
      and t3.clientID = 6 
  group by
    t1.Category,
    t2.condition