user_id的列名错误

Question

My users table has the columns user_id , email My invites table has the columns invite_id request_id user_id sent_time

When I run the following query, I get the two tables joined into 1, which is expected.

'SELECT * FROM users INNER JOIN invites ON users.user_id = invites.user_id'

However, when I run the following query,

'SELECT user_id FROM users INNER JOIN invites ON users.user_id = invites.user_id'

I get the following error

OperationalError: (sqlite3.OperationalError) ambiguous column name: user_id [SQL: 'SELECT user_id FROM users INNER JOIN invites ON users.user_id = invites.user_id']

Any help appreciated.

Answer 1

I think the message is pretty clear. SQLite doesn't know what table user_id is coming from.

One simple solution is to qualify the column name usinga table alias:

SELECT u.user_id
FROM users u INNER JOIN
     invites i
     ON u.user_id = i.user_id;

Another method is to use USING rather than ON :

SELECT user_id
FROM users u INNER JOIN
     invites i
     USING (user_id);

Answer 2

You need to qualify the column name with table name like below cause both table involved in query have the same column name

SELECT `users`.user_id 
FROM users 
INNER JOIN invites ON `users`.user_id = invites.user_id

Answer 3

This means you need to be specific about which user_id column you want to display. Even though they're joined that doesn't guarantee they're identical. Some types of joins allow NULL values on one side of the match (eg LEFT JOIN ), so you need to ask for a particular value:

SELECT users.user_id FROM users INNER JOIN invites ON users.user_id = invites.user_id