Why Does MySQL Throw the 'Every Derived Table Must Have Its Own Alias' Error?

Understanding the "Every Derived Table Must Have Its Own Alias" Error in MySQL

When running a query involving nested sub-queries, MySQL sometimes throws an error stating "Every derived table must have its own alias." This error alerts you to an issue with the sub-queries' structure.

To rectify this error, each sub-query (or derived table) must have a unique alias. This alias serves as an identifier, allowing the outer query to reference the sub-query's results.

For instance, consider the following query:

SELECT ID FROM (
    SELECT ID, msisdn
    FROM (
        SELECT * FROM TT2
    )
);

Here, the error occurs because the innermost sub-query (the one selecting from TT2) does not have an alias. To resolve it, assign an alias to this sub-query, as shown below:

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

The alias "T" now allows the outer query to refer to the innermost sub-query's results, effectively eliminating the error.

In many cases, the query can be simplified by removing the unnecessary sub-queries, as in this example:

SELECT ID FROM TT2

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