Question

I tried to work out around this. But I think I am getting no where.

I have 3 tables:

This tale contains all questions and question types:

    Table: Ref
    id    |    type   |   info
    ==========================
    1          SS         Education
    ---------------------------
    2          RB         Gender
    ---------------------------
    3          ST         State

This table contains “options” for the questions in the above table ‘Ref`

    Table: ref_ans
    id    |  q_id   |   answer_text
    ===========================
    1          1        Masters     
    ---------------------------
    2          1        Bachelors     
    ---------------------------
    3          1        Undergrad
    ---------------------------
    4          2        Male     
    ---------------------------
    5          2        Female
    ---------------------------
    6          2        Dont want to disclose

This table contains states (type =”ST” in table Ref)

    Table: us_states

    id    |  answer_text 
    ===========================
    1        Alaska     
    ---------------------------
    2        Alabama     
    ---------------------------
    3        Arkansan
    ---------------------------
    4        Arizona     
    ---------------------------
    5        Baltimore
    ---------------------------
    etc

The result I want is:

    ref.id, ref_ans.id, ref.answer_text / us_states.answer_text

*for a given ref.question_id *.

And the condition is: If the question_id, for which the answers requested is ‘ST’, it should pull the answers from us_states, otherwise, it should pull from ref-ans table.

I tried this. Obviously, this did not work:

    SELECT ref.id, 
         CASE WHEN ref.type = 'ST' THEN 
             (SELECT ID, answer_text FROM us_states )
         ELSE 
             (SELECT id, answer_text FROM ref_ans)  
    END

    FROM ref
   WHERE ref.ID = <id>

Any ideas?

Answer 1

Try:

SELECT    a.id, 
          COALESCE(b.id, c.id) AS ans_id,
          COALESCE(b.answer_text, c.answer_text) AS answer_text
FROM      ref a
LEFT JOIN ref_ans b ON a.id = b.q_id
LEFT JOIN us_states c ON a.type = 'ST'
WHERE     a.id = <id> AND (
              (a.type <> 'ST' AND b.id IS NOT NULL) OR
              (a.type =  'ST' AND c.id IS NOT NULL)
          )