字段列表中的“user_id”列不明确

Question

I am attempting to get the user information of the user who left this review.

With the following code:

SELECT username, image, user_id FROM table_users AS us
JOIN table_reviews AS re
ON re.user_id = us.user_id
WHERE us.user_id = 1 AND
re.review_id= 1

I get the error:

Column 'user_id' in field list is ambiguous

What does this mean?

Answer 1

It means that both tables in the query have the column user_id .

You need to specify which one you want to get in the SELECT statement like SELECT username, image, re.user_id

Answer 2

column user_id is in both table_reviews , table_users tables.

You need to specify columns with table alias name also.

SELECT username, image, us.user_id FROM table_users AS us
JOIN table_reviews AS re
ON re.user_id = us.user_id
WHERE us.user_id = 1 AND
re.review_id= 1

Answer 3

It means column user_id is in both tables ie, in table_reviews, table_users

Try like this:

SELECT username, image, us.user_id    //or re.user_id
FROM table_users AS us
JOIN table_reviews AS re
ON re.user_id = us.user_id
WHERE us.user_id = 1 AND
re.review_id= 1

Answer 4

Not only selected values(SELECT username, image, user_id) are examined in where clause (WHERE us.user_id = 1), all joined columns are examined in where clause, so in your example you have user_id column in both joined tables. If you have query like this one:

SELECT table_reviews.id FROM table_users AS us
JOIN table_reviews AS re
ON re.user_id = us.user_id
WHERE id

id will be ambiguous because id-s from table_reviews and table_reviews will be examined in where clause although only id from table_reviews is selected.

Answer 5

This is because user_id field exists in both tables. You need to specify which table's user_id you want.

SELECT username, image, re.user_id