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Description

PostgreSQL Error 42712, 'duplicate alias', indicates a syntax error where an alias (a temporary name for a table or column) is defined more than once within the same query scope. This prevents the database from unambiguously resolving object references, leading to query failure and preventing execution.

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Error Message

duplicate alias

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Known Causes

3 known causes

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Duplicate Table Aliases

Assigning the same alias to multiple tables within a single `FROM` clause or `JOIN` operation, making it impossible for the database to distinguish between them.

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Duplicate Column Aliases

Defining the same alias for different columns or expressions in the `SELECT` list of a query, leading to ambiguity in the result set.

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Conflicting Subquery Aliases

An alias used in an outer query or a correlated subquery conflicts with an alias defined within another part of the same query scope, even if they are logically distinct.

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Solutions

4 solutions available

1. Rename Conflicting Aliases easy

Identify and rename duplicate aliases within your SQL query to ensure uniqueness.

1

Examine your SQL query carefully. Look for any column names or expressions that are given the same alias. Aliases are typically assigned using the `AS` keyword or by simply providing a name after the expression.

2

If you find a duplicate alias, modify the query to assign a unique name to one or both of the conflicting aliases. Choose names that are descriptive and easily distinguishable.

SELECT
    column1 AS alias_a,
    column2 AS alias_b,
    column3 AS alias_a -- This will cause the error
FROM
    your_table;

3

Correct the query by renaming the duplicate alias.

SELECT
    column1 AS alias_a,
    column2 AS alias_b,
    column3 AS alias_c -- Renamed to a unique alias
FROM
    your_table;

2. Remove Redundant Aliases easy

Eliminate unnecessary aliases, especially in simple `SELECT *` statements or when aliases are implicitly unique.

1

Review your query for aliases that might be redundant. This is common in `SELECT *` queries where PostgreSQL might implicitly assign aliases, or when you've aliased a column with its own name.

2

If an alias is simply repeating the column name and isn't required for clarity or to resolve ambiguity (e.g., in joins), consider removing it.

SELECT
    column1 AS column1,
    column2 AS alias_b
FROM
    your_table;

3

Modify the query to remove the redundant alias.

SELECT
    column1,
    column2 AS alias_b
FROM
    your_table;

3. Qualify Column Names in Joins medium

When joining tables, explicitly qualify column names with table aliases to avoid ambiguity and duplicate alias errors.

1

This error often occurs when joining multiple tables that have columns with the same name, and you've assigned aliases to these columns without proper qualification.

2

Ensure that when you select columns that might have the same name across joined tables, you prefix the column name with the table's alias.

SELECT
    t1.id AS item_id,
    t2.id AS order_id,
    t1.name AS item_name,
    t2.name AS order_name -- Potential conflict if 'name' is also in t1
FROM
    items t1
JOIN
    orders t2 ON t1.order_id = t2.id;

3

If `t1.name` and `t2.name` are intended to be distinct, ensure they have unique aliases. If they are intended to be the same conceptual field, pick one and qualify it appropriately.

SELECT
    t1.id AS item_id,
    t2.id AS order_id,
    t1.name AS item_name,
    t2.created_at AS order_created_at
FROM
    items t1
JOIN
    orders t2 ON t1.order_id = t2.id;

4. Review Subqueries and CTEs for Alias Conflicts medium

Check for duplicate aliases within subqueries or Common Table Expressions (CTEs) that might be surfaced as duplicate aliases in the outer query.

1

If your query involves subqueries or CTEs, the duplicate alias error might originate from within these nested structures. Aliases defined inside a subquery or CTE need to be unique within their scope.

2

Carefully inspect the `SELECT` lists of all subqueries and CTEs for any repeated aliases.

WITH my_cte AS (
    SELECT
        column_a AS common_alias,
        column_b
    FROM
        table1
)
SELECT
    cte.common_alias,
    another_table.column_c AS common_alias -- Duplicate alias from CTE
FROM
    my_cte cte
JOIN
    another_table ON cte.column_b = another_table.column_d;

3

Rename the duplicate alias within the subquery or CTE, or in the outer query if the intention is to distinguish them.

WITH my_cte AS (
    SELECT
        column_a AS cte_alias,
        column_b
    FROM
        table1
)
SELECT
    cte.cte_alias,
    another_table.column_c AS another_alias
FROM
    my_cte cte
JOIN
    another_table ON cte.column_b = another_table.column_d;

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Related Errors

5 related errors

PostgreSQL Error 42712: Duplicate Alias in SQL Query