What is the error “Every derived table must have its own alias” in MySQL?

Question

I am running this query on MySQL

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

and it is giving this

Answer 1

Here's a different example that can't be rewritten without aliases ( can't GROUP BY DISTINCT).

Imagine a table called purchases that records purchases made by customers at stores, i.e. it's a many to many table and the software needs to know which customers have made purchases at more than one store:

SELECT DISTINCT customer_id, SUM(1)
  FROM ( SELECT DISTINCT customer_id, store_id FROM purchases)
  GROUP BY customer_id HAVING 1 < SUM(1);

..will break with the error Every derived table must have its own alias. To fix:

SELECT DISTINCT customer_id, SUM(1)
  FROM ( SELECT DISTINCT customer_id, store_id FROM purchases) AS custom
  GROUP BY customer_id HAVING 1 < SUM(1);

( Note the AS custom alias).