Why Does MySQL Throw an "Ambiguous User ID in WHERE Clause" Error?

Ambiguous User ID in MySQL WHERE Clause

When executing a MySQL query with a WHERE clause using the 'user_id' field, you may encounter the error message "user_id in where clause is ambiguous." This occurs because the query cannot determine which 'user_id' field to use since there are multiple tables with columns named 'user_id'.

To correct this, you need to specify which 'user_id' field to use by including the table name as a prefix. For instance, in the given query:

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

The query uses the same 'user_id' field name in both the JOIN condition and the WHERE clause. To resolve the ambiguity, specify the table name before 'user_id' in the WHERE clause:

... WHERE user.user_id=1

This explicitly indicates that the 'user_id' field from the 'user' table should be used in the WHERE clause.

Specifying the table name removes the ambiguity, allowing MySQL to execute the query correctly. By doing so, you ensure that the query retrieves data from the intended fields and tables.

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