How to Solve SQL Error 1066: Non-Unique Table Aliases in JOINs?

SQL Error 1066: Troubleshooting Non-Unique Table Aliases in JOIN Queries

When encountering SQL error 1066, "Not unique table/alias," it indicates that multiple occurrences of the same table are used without unique aliases to differentiate them in a JOIN query.

Consider the following example code:

SELECT article.* , section.title, category.title, user.name, user.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 ON article.modified_by = user.id
WHERE article.id = '1'

In this code, you'll notice that the "user" table is joined twice, causing the error. To resolve this issue, you need to give a unique alias to the second occurrence of the table.

The following code demonstrates the corrected query:

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'

By providing the unique alias "u2" to the second occurrence of the "user" table, the error is resolved, and you can successfully execute the query.

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