1052：在以下情况下，字段列表中的列“ user_id”不明确

Question

I have 3 tables which share a user id, now I want to get data from all 3 but I don't know where I'm doing it wrong in this query

SELECT user_id, first_name, image_id, description, gender 
FROM users a 
JOIN user_services b ON b.user_id = a.user_id 
JOIN user_timeframe c ON c.user_id = a.user_id

Answer 1

Two key best practices:

• Always qualify all column references.
• Use table aliases that are meaningful rather than arbitrary letters.

So:

SELECT u.user_id, u.first_name, ?.image_id, ?.description, 
       u.gender 
FROM users u JOIN
     user_services us
     ON us.user_id = u.user_id JOIN
     user_timeframe ut
     ON ut.user_id = u.user_id;

The ? is because it is not clear what table those columns come from. (The other columns are guesses so they might not be right either.)

Answer 2

The preferred way should be explicit aliasing. There is another way to fix this query by using JOIN ... USING syntax:

SELECT user_id, first_name, image_id, description, gender 
FROM users a 
JOIN user_services b USING(user_id)
JOIN user_timeframe c USING(user_id);

db<>fiddle demo