Question

I have a short access/mySQL question. I have a mapping table on the format below.

ID      Category_A      Category_B      Category_C      Team
 1              a               b                         T1
 2              a                               d         T2

I have a second table which also includes Category_A, Category_B, and Category_C. I would like to join the Team value to the my second table based on the mappingtable. My problem is that when there is a blank (e.g. ID=2, Category_B) the mapping should assign the T2 to any row that contains Category_A=a and Category_C=d regardless of the value in Category_B.

Can this type of mapping be done?

Grateful for your help!

Answer 1

In MS Access, I think you would need something on the lines of:

SELECT t.ID, m.Team
FROM Team t
 INNER JOIN Mapping m
      ON (m.Category_C = t.Category_C) 
     AND (m.Category_B = t.Category_B) 
     AND (m.Category_A = t.Category_A)
WHERE m.Category_C Is Not Null
     AND m.Category_B Is Not Null 
     AND m.Category_A Is Not Null

UNION ALL
SELECT t.ID, m.Team
FROM Team t
 INNER JOIN Mapping m
      ON  (m.Category_B = t.Category_B) 
     AND (m.Category_A = t.Category_A)
WHERE m.Category_C Is Null
     AND m.Category_B Is Not Null 
     AND m.Category_A Is Not Null

UNION ALL
SELECT t.ID, m.Team
FROM Team t
 INNER JOIN Mapping m
      ON (m.Category_C = t.Category_C)
     AND (m.Category_A = t.Category_A)
WHERE m.Category_C Is Not Null
     AND m.Category_B Is Null 
     AND m.Category_A Is Not Null

UNION ALL
SELECT t.ID, m.Team
FROM Team t
 INNER JOIN Mapping m
      ON (m.Category_C = t.Category_C) 
     AND (m.Category_B = t.Category_B) 
WHERE m.Category_C Is Not Null
     AND m.Category_B Is Not Null 
     AND m.Category_A Is Null