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Description

This PostgreSQL error indicates that a column name in your SQL query is present in multiple tables or aliases referenced in the FROM clause, making it unclear to the database which specific column you intend to use. It commonly arises in SELECT, WHERE, JOIN, GROUP BY, or ORDER BY clauses when column references are not adequately qualified.

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Error Message

ambiguous column

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Known Causes

3 known causes

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Unqualified Column in Joins

A column name is used without a table alias or name in a query involving multiple tables where that column exists in more than one of the joined tables.

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Conflicting Aliases or Self-Joins

When performing a self-join or using multiple aliases for the same table, column references are not distinct enough for each instance of the table.

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Subquery/CTE Column Collision

A column name within a subquery or Common Table Expression (CTE) unintentionally matches a column name in the outer query or another referenced CTE.

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Solutions

4 solutions available

1. Qualify Column with Table Name easy

Specify which table the column belongs to

1

Use table.column format

-- Wrong:
SELECT id, name FROM users u JOIN orders o ON id = user_id

-- Right:
SELECT u.id, u.name FROM users u JOIN orders o ON u.id = o.user_id

2. Use Table Aliases easy

Define and use short aliases

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Use aliases for clarity

SELECT 
  u.id AS user_id,
  o.id AS order_id,
  u.created_at AS user_created,
  o.created_at AS order_created
FROM users u
JOIN orders o ON u.id = o.user_id;

3. Fix GROUP BY Ambiguity easy

Qualify columns in GROUP BY

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Specify table for grouped columns

SELECT u.name, COUNT(o.id) as order_count
FROM users u
JOIN orders o ON u.id = o.user_id
GROUP BY u.name;  -- Not just: GROUP BY name

4. Fix ORDER BY Ambiguity easy

Qualify columns in ORDER BY

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Specify table or use alias

SELECT u.name, o.total
FROM users u
JOIN orders o ON u.id = o.user_id
ORDER BY u.name, o.created_at;

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Related Errors

5 related errors

PostgreSQL Error 42702: Ambiguous Column Reference