Question

MySQL setup: step by step.

programs -> linked to –> speakers (by program_id)

At this point, it’s easy for me to query all the data:

SELECT * 
FROM programs 
JOIN speakers on programs.program_id = speakers.program_id

Nice and easy.

The trick for me is this. My speakers table is also linked to a third table, “books.” So in the “speakers” table, I have “book_id” and in the “books” table, the book_id is linked to a name.

I’ve tried this (including a WHERE you’ll notice):

SELECT *
FROM programs
JOIN speakers on programs.program_id = speakers.program_id
JOIN books on speakers.book_id = books.book_id
WHERE programs.category_id = 1
LIMIT 5

No results.

My questions:

1. What am I doing wrong?
2. What’s the most efficient way to make this query?

Basically, I want to get back all the programs data and the books data, but instead of the book_id, I need it to come back as the book name (from the 3rd table).

Thanks in advance for your help.

UPDATE:
(rather than opening a brand new question)

The left join worked for me. However, I have a new problem. Multiple books can be assigned to a single speaker.

Using the left join, returns two rows!! What do I need to add to return only a single row, but separate the two books.

Answer 1

is there any chance that the books table doesn’t have any matching columns for speakers.book_id?

Try using a left join which will still return the program/speaker combinations, even if there are no matches in books.

SELECT *
FROM programs
JOIN speakers on programs.program_id = speakers.program_id
LEFT JOIN books on speakers.book_id = books.book_id
WHERE programs.category_id = 1
LIMIT 5

Btw, could you post the table schemas for all tables involved, and exactly what output (or reasonable representation) you’d expect to get?

Edit: Response to op author comment

you can use group by and group_concat to put all the books on one row.

e.g.

SELECT speakers.speaker_id, 
       speakers.speaker_name, 
       programs.program_id, 
       programs.program_name,
       group_concat(books.book_name)
FROM programs
JOIN speakers on programs.program_id = speakers.program_id
LEFT JOIN books on speakers.book_id = books.book_id
WHERE programs.category_id = 1
GROUP BY speakers.id
LIMIT 5

Note: since I don’t know the exact column names, these may be off