How can I join three tables in MS Access SQL? - sql

Question

I have a simple table model with 3 tables but I am not able to join them in the way I need it.
Table: TOPIC
ID TITLE
1 Talk1
2 Talk2
3 Talk3
4 Talk4
Table: SPEAKER
ID NAME
20 Speaker20
21 Speaker21
22 Speaker22
23 Speaker23
Table: CONNECTOR
ID_TOPIC ID_SPEAKER
1 21
2 23
2 22
2 21
4 20
4 22
In Table CONNECTOR the Topics are getting assigned to speakers.
One Topic can be assigned to different speakers.
There can also be topics in the TOPIC table which are not assigned yet, like in this example topic 3.
What I need is an SQL which give me as result all topics from the TOPICS table with the assigned speakers with name but I also want the topics in the result list which are not assigned through the CONNECTOR table.
How should the join look like to get this result?

Answer 1

I did an example in Access and got this:
As you can see, the query lists all topics, even if there is no speaker assigned. The SQL code of my query is this:
SELECT TOPICS.Title, SPEAKER.SpeakerName
FROM SPEAKER RIGHT JOIN (CONNECTOR RIGHT JOIN TOPICS ON CONNECTOR.ID_TOPIC = TOPICS.Id) ON SPEAKER.ID = CONNECTOR.ID_SPEAKER;
Hope this helps
UPDATE: Please, note that in table SPEAKERS, I've used as fieldname SpeakerName instead of Name because Name it's a reserved word, and it can create some troubles using it.

Answer 2

Look for
SELECT TOPIC.TITLE, SPEAKER.NAME
FROM ( CONNECTOR
INNER JOIN TOPIC ON TOPIC.ID = CONNECTOR.ID_TOPIC)
INNER JOIN SPEAKER ON CONNECTOR.ID_SPEAKER = SPEAKER.ID
UNION ALL
SELECT NULL, SPEAKER.NAME
FROM SPEAKER
LEFT JOIN CONNECTOR ON CONNECTOR.ID_SPEAKER = SPEAKER.ID
WHERE CONNECTOR.ID_TOPIC Is Null
UNION ALL
SELECT TOPIC.TITLE, NULL
FROM TOPIC
LEFT JOIN CONNECTOR ON TOPIC.ID = CONNECTOR.ID_TOPIC
WHERE CONNECTOR.ID_TOPIC Is Null;