Why is my MySQL WHERE clause with 'user_id' ambiguous?

Ambiguous 'user_id' Column in MySQL WHERE Clause

When executing the following MySQL query, you may encounter an error indicating that the 'user_id' column in the WHERE clause is ambiguous:

SELECT user.*, user_info.*
FROM user
INNER JOIN user_info ON user.user_id = user_info.user_id
WHERE user_id=1

Reason for the Error:

This error occurs because both the 'user' and 'user_info' tables have a column named 'user_id'. Without specifying which table's 'user_id' to use in the WHERE clause, MySQL is unable to determine which column to reference.

Solution:

To resolve this ambiguity, you need to explicitly specify which column to use by prepending the table name before the 'user_id' column:

SELECT user.*, user_info.*
FROM user
INNER JOIN user_info ON user.user_id = user_info.user_id
WHERE user.user_id=1

By prepending 'user.' before 'user_id,' you specify that the 'user_id' column from the 'user' table should be used in the WHERE clause. This eliminates the ambiguity and allows MySQL to correctly execute the query.

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