Including values NOT FOUND in MySQL query results

Question

I have the following MySQL tables:

tbl_pet_owners:

+----+--------+----------+--------+--------------+
| id | name   | pet      | city   | date_adopted |
         


        

Answer 1

Then perform a RIGHT JOIN instead of LEFT JOIN saying

RIGHT JOIN tbl_pet_types types ON owners.pet = types.pet

In case you want outer joined result for both table (which not sure off), you can then consider doing a FULL JOIN by mixing right and left join

Answer 2

Does MySQL STILL not have CTEs? They make life so much easier.

Regardless, to get 'NOT FOUND', use coalesce() in your SELECT.

SELECT DISTINCT p.petType
    , coalesce(po.name,'NOT FOUND') AS name
    , coalesce(po.city,'NOT FOUND') AS city
FROM (
    SELECT 'mammal' AS petType UNION ALL
    SELECT 'fish' UNION ALL
    SELECT 'amphibian' UNION ALL
    SELECT 'seacreature'
) p
LEFT OUTER JOIN (  
    SELECT tpo.name, tpo.city, pt.type AS petType
    FROM tbl_pet_owners tpo
    LEFT OUTER JOIN tbl_pet_types tpt ON tpo.pet = tpt.pet
) po ON p.petType = po.petType

I don't have a MySQL machine to test this on, but something like this should give you what you're looking for.

Answer 3

A left join is correct, but you need for the types to be first:

SELECT DISTINCT types.type, owners.name, owners.city
FROM tbl_pet_types types LEFT JOIN
     tbl_pet_owners owners
     ON owners.pet = types.pet
WHERE types.type IN ('mammal', 'fish', 'amphibian', 'seacreature');

Because the WHERE clause refers only to tbl_pet_types, it does not change.

How left join works is simple: It keeps all rows in the first table. Unmatched columns in the second become NULL.

EDIT:

If you have a list of types that are not in tbl_pet_types, then you need a left join with all the values in a derived table:

SELECT DISTINCT tt.type, po.name, po.city
FROM (SELECT 'mammal' as type UNION ALL
      SELECT 'fish' as type UNION ALL
      SELECT 'amphibian' as type UNION ALL
      SELECT 'seacreature' as type 
     ) tt left join
     tbl_pet_types pt
     ON pt.type = tt.type LEFT JOIN
     tbl_pet_owners po
     ON po.pet = pt.pet;