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Description

Error 1248 indicates that a subquery used as a derived table within a `FROM` or `JOIN` clause lacks a required alias. MySQL mandates an alias for all derived tables to ensure proper referencing of their columns and to maintain SQL standard compliance.

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Error Message

Every derived table must have its own alias

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Known Causes

3 known causes

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Missing Alias in FROM Clause

A subquery used directly in the `FROM` clause of a SQL statement was not assigned a temporary name (alias).

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Derived Table in JOIN Lacks Alias

A subquery acting as a derived table within a `JOIN` operation (e.g., `LEFT JOIN`, `INNER JOIN`) was not given an alias.

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Alias Omission After Subquery

The `AS` keyword and the subsequent alias name were simply forgotten or omitted after defining a subquery that serves as a derived table.

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Solutions

3 solutions available

1. Assign an Alias to the Derived Table easy

The most direct solution is to provide a unique alias to the subquery used as a derived table.

1

Locate the subquery that is being used as a derived table. This is typically a `SELECT` statement enclosed in parentheses and immediately followed by another `SELECT` statement or a `JOIN` clause.

2

After the closing parenthesis of the subquery, add a unique alias. This alias will be used to refer to the results of the subquery.

SELECT ... FROM (SELECT column1, column2 FROM your_table) AS derived_table_alias WHERE derived_table_alias.column1 = 'some_value';

3

Ensure that all references to columns within the derived table in the outer query use this new alias.

SELECT derived_table_alias.column1, other_table.column3 FROM (SELECT column1, column2 FROM your_table) AS derived_table_alias JOIN other_table ON derived_table_alias.column2 = other_table.column2;

2. Use a Common Table Expression (CTE) Instead medium

For more complex queries or better readability, refactor the derived table into a Common Table Expression (CTE).

1

Identify the subquery that is causing the error. This subquery will become your CTE.

2

Define the CTE using the `WITH` clause, giving it a name (which acts as its alias).

WITH cte_name AS (
  SELECT column1, column2 FROM your_table
)

3

Write your main query referencing the CTE by its name.

WITH cte_name AS (
  SELECT column1, column2 FROM your_table
)
SELECT column1, column3 FROM cte_name JOIN other_table ON cte_name.column2 = other_table.column2;

3. Simplify the Query to Avoid Derived Tables medium

If possible, restructure the query to eliminate the need for a derived table altogether.

1

Analyze the purpose of the derived table. What data is it intended to provide to the outer query?

2

Consider if the same result can be achieved by using `JOIN` operations directly on the base tables. Sometimes, a derived table is used to pre-filter or aggregate data, which can often be integrated into the main query's `WHERE` or `GROUP BY` clauses.

Original Query (with derived table):
SELECT dt.column1 FROM (SELECT column1, column2 FROM your_table WHERE column2 > 10) AS dt;

Refactored Query (without derived table):
SELECT column1 FROM your_table WHERE column2 > 10;

3

If the derived table involves aggregations, explore if `HAVING` clauses or subqueries in the `SELECT` list can achieve the same without a full derived table.

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Related Errors

5 related errors

MySQL Error 1248: Missing Alias for Derived Table