Does it matter to filter results when doing aggregation?

byMR

May 14, 2022

I want to get my sales for each day which is located in my orders_summary table.

orders_summary table columns: id, date, amount, sku_id

products table columns: id, sku

Currently Im getting my daily sales like this:

SELECT
    MAX(CASE WHEN os.date = '01/01/2022' THEN COALESCE(amount,0)::INT ELSE 0 END) AS orders_1,
    MAX(CASE WHEN os.date = '01/02/2022' THEN COALESCE(amount,0)::INT ELSE 0 END) AS orders_2
FROM products AS p
LEFT JOIN orders_summary AS os ON p.id = os.sku_id
WHERE p.id = '1'
GROUP BY p.id;

Is it important to add AND date BETWEEN '01/01/2022' AND '01/02/2022' in my where clause?

>Solution :

Yes absolutely. Imagine having 10 years worth of data in the table where you’re only interested in the data for two days. You must use the where clause which restricts the number of rows (down to 0.05% in this case) before doing the group by.