How to Fix the 'subquery in FROM must have an alias' Error in PostgreSQL?

Resolving "subquery in FROM must have an alias" Error in PostgreSQL

When attempting to execute a query involving a parenthesized subquery within the FROM clause, it's crucial to ensure that an alias is assigned to the subquery. This requirement is encountered when utilizing PostgreSQL, as exemplified by the error message:

ERROR: subquery in FROM must have an alias

To rectify this issue, simply append an alias to the subquery, ensuring to place it after the closing parenthesis. Here's a corrected version of the provided query:

SELECT COUNT(made_only_recharge) AS made_only_recharge
FROM    
    (
        SELECT DISTINCT (identifiant) AS made_only_recharge
        FROM cdr_data
        WHERE CALLEDNUMBER = '0130'
        EXCEPT
        SELECT DISTINCT (identifiant) AS made_only_recharge
        FROM cdr_data
        WHERE CALLEDNUMBER != '0130'
    ) AS derivedTable   -- Alias assignment

By incorporating this modification, the query should execute without error in PostgreSQL. An alias provides a distinct name for the subquery, enabling the database to distinguish it from other elements within the query. It's a crucial aspect when using subqueries in the FROM clause of a PostgreSQL query.

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