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

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;