How to Resolve 'user_id' Ambiguity in MySQL WHERE Clause?

Ambiguous 'user_id' in MySQL WHERE Clause

When querying a database with multiple tables that share common column names, it's crucial to explicitly specify which table's column you're referring to in the WHERE clause. This ambiguity arises when tables like 'user' and 'user_info' have a shared column name, such as 'user_id'.

The Problem

The query below attempts to join the 'user' and 'user_info' tables, but it results in the error "'user_id' in 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

The Solution

To resolve this ambiguity, you must specify which table's 'user_id' column you're comparing to the value 1. This is done by prefixing the column name with the table alias:

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

By explicitly specifying 'user.user_id', you're informing the database that this is the column you want to filter on, not the 'user_id' column from the 'user_info' table. This eliminates the ambiguity and allows the query to execute successfully.

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