Question

I currently have the following SQL statement:

SELECT s.first_name, s.last_name, tgs.group_identifier
FROM staff s
JOIN staff_training st
ON s.staff_id = st.staff_id
JOIN training_group_staff tgs
ON st.staff_training_id = tgs.staff_training_id
WHERE st.staff_course_id = '164'

training_group_staff only contains the staff_training_id and training_group_id

This statement works as expected and returns all staff names attending course 164 AND have been placed into a group (identified with the group_identifier field).

What I am attempting to do is display all users on training course 164 and if no group selected (there won’t be a row for the specific staff_training_id in training_group_staff) then return null for that column.

Visual Example

Current Statement Returns:

first_name  |  last_name  |  group_identifier
 Jim        |   Jones     |   3
 Harry      |   Jones     |   6

What I am attempting to return is:

first_name  |  last_name  |  group_identifier
 Jim        |   Jones     |   3
 Harriet    |   Smith     |   NULL   // No row in training_group_staff
 Harry      |   Jones     |   6

I have tried several joins, however seem to return the same results – is the desired output possible in one query?

Answer 1

Try with LEFT JOIN. Should be what you’re after.