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HAVING

When we need to filter the results of a GROUP BY query even further, we can use the HAVING clause. HAVING specifies a search condition for a group.

The HAVING clause is similar to the WHERE clause, but it operates on groups after they've been grouped, rather than rows before they've been grouped.

SELECT album_id, COUNT(id) AS count
FROM songs
GROUP BY album_id
HAVING COUNT(id) > 5;

This query returns the album_id and count of its songs, but only for albums with more than 5 songs.

Assignment

A new page in the CashPal app allows users to see how much money they've spent on a specific kind of transaction, and alerts them if that amount is fairly large. Let's write a query on the transactions table that returns the total amount spent by each user on lunch when that balance is greater than 20.

Your query should:

Return a sender_id (the person spending money) and a balance.
The balance is the SUM() of all amounts.
Don't return any rows that have a NULL sender_id.
Only return transactions that were successful.
The note must contain the word lunch to be part of the aggregation.
Group by sender_id.
The aggregated balance must be greater than 20.
Order the results by the balance in ascending order.