How to Fix the 'Not unique table/alias: 'user'' SQL Error?

How to resolve "Not unique table/alias: 'user'" error in SQL?

The SQL code you provided gives error 1066 because the 'user' table is referenced twice without an alias. In SQL, when joining tables, it's essential to give tables unique aliases if they are referenced multiple times.

Your table structure shows that the 'user' table contains columns such as 'name' and 'id'. You have joined the 'article' table with the 'user' table to retrieve user information based on 'author_id'. However, you have also left-joined the 'article' table with the 'user' table again, but this time based on 'modified_by'. Without providing an alias for the second instance of the 'user' table, the query cannot differentiate between the two uses of 'user'.

To resolve this issue, you need to give the second instance of the 'user' table an alias. This will distinguish between the two instances and allow SQL to correctly identify the columns you want to retrieve.

Here is the modified code:

SELECT article.*, section.title, category.title, user.name, u2.name
FROM article
INNER JOIN section ON article.section_id = section.id
INNER JOIN category ON article.category_id = category.id
INNER JOIN user ON article.author_id = user.id
LEFT JOIN user u2 ON article.modified_by = u2.id
WHERE article.id = '1'

In this modified code, we have given the second instance of the 'user' table the alias 'u2'. This allows the query to differentiate between the two occurrences of the 'user' table and retrieve the desired data correctly.

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