Whats better; mysql scheduler or php script and crontab? - php

Question

I have 1 mysql table where it has thousands of rows. I use this as a transaction history for my users. I also query this table on the same page for a sum of earnings per product. here are my two mysql calls;
$earnperproduct = mysqli_query($con,"SELECT product, SUM(amount) AS totalearn FROM wp_payout_history WHERE user=$userid GROUP BY product");
$result = mysqli_query($con,"SELECT * FROM wp_payout_history WHERE user=$userid ORDER BY date DESC");
my fear is that as the table grows, the $earnperproduct call will become too intensive and slow down page loading. Therefore instead of doing a sum command every time the page loads, i think it would be easier to update a summary (example wp_summary_table) whenever wp_payout_history is changed to replace past values with new SUM(AMOUNT)values per user and product; and thus query something like this;
$earnperproduct = mysqli_query($con,"SELECT * FROM wp_payout_summary_table WHERE user=$userid ORDER BY product DESC");
TL;DR
What is the best method to go about updating a table using the $earnedperproduct style call? would I be better using mysql event scheduler or a php script with a crontab? Is there any tutorials that can help me create either option for my needs?

Answer 1

Both the control mechanisms you mention use time as the trigger for an action. But your description says that you really want to trigger an action when the data changes. And in a relational database the best way to trigger an action when data is changed is with a ....trigger. Which makes your question a duplicate of this.
Arguably it may be more efficient to snapshot the transactions, then something like....
[INSERT INTO summary_table (user, total_amount, last_id) ]
SELECT
user, SUM(amount), MAX(id)
FROM (
SELECT a.user, a.total_amount AS amount, a.last_id
FROM summary_table a
WHERE a.user=$user_id
AND last_id=(SELECT MAX(b.last_id)
FROM summary_table b
WHERE b.user=$user_id)
UNION
SELECT h.user, h.amount, h.id
FROM wp_payout_history h
WHERE h.user=$user_id
AND h.id>(SELECT MAX(c.last_id)
FROM summary_table c
WHERE c.user=$user_id)
) ilv
GROUP BY user;
...then it doesn't really matter what you use to refresh the history - the query will always give you an up to date response. If you go down this route then add a dummy integer column in the summary table and add 0 as unaggregatedrows to the second SELECT and SUM(1) to the 4th SELECT to work out when it will be most efficient to update the summary table.