Why Does MySQL Throw 'Every Derived Table Must Have Its Own Alias' and How Do I Fix It?

Every Derived Table Requires an Alias Error in MySQL

MySQL can throw an error stating "Every derived table must have its own alias" when executing nested queries. This error occurs because derived tables, also known as subqueries, must be uniquely identified within the outer query.

The error is caused when a derived table lacks an alias, preventing it from being referenced unambiguously in the outer query. An alias assigns a temporary name to a derived table, enabling it to be used independently.

To resolve the error, provide an alias for each derived table using the AS keyword. In the following example, the derived table is aliased as "T":

SELECT ID FROM (
    SELECT ID, msisdn FROM (
        SELECT * FROM TT2
    ) AS T
) AS T

Note that the query can be further simplified to:

SELECT ID FROM TT2

By specifying aliases, you can avoid ambiguity and ensure that MySQL can properly execute nested queries.

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