MySQL query to get table name with numerically highest number

Question

I have a WordPress multisite database, which has a lot of orphan tables I need to get rid of. The names are structured like this. The number in the table name is the site ID.

wp_9892_wc_booking_relationships
wp_10001_wc_booking_relationships
wp_18992_wc_deposits_payment_plans
wp_20003_followup_coupons
wp_245633_followup_coupon_logs

I want to make a query to find out the highest site ID from the table names.

I've tried queries like this

SELECT table_name FROM information_schema.tables
WHERE table_type = 'base table'
AND table_name REGEXP '^wp_[0-9]+_[a-z0-9]+'
ORDER BY table_name DESC
LIMIT 1; 

But that sorts the results in an unexpected way: I get

wp_9_woocommerce_log

When with LIMIT 10 I see there are names with higher numbers:

wp_99_woocommerce_log
wp_999_woocommerce_log
wp_999_wc_webhooks
wp_999_wc_download_log
wp_999_wcpv_per_product_shipping_rules
wp_999_wcpv_commissions
wp_9999_wcpv_per_product_shipping_rules
wp_9999_wcpv_commissions
wp_9998_wc_points_rewards_user_points_log

Is this something that's doable with a SQL query?

Answer 1

Consider the following data example.

CREATE TABLE test(
table_name  varchar(255) );

insert into test values
('wp_99_woocommerce_log'),
('wp_999_woocommerce_log'),
('wp_999_wc_webhooks'),
('wp_999_wc_download_log'),
('wp_999_wcpv_per_product_shipping_rules'),
('wp_999_wcpv_commissions'),
('wp_9999_wcpv_per_product_shipping_rules'),
('wp_9999_wcpv_commissions'),
('wp_9998_wc_points_rewards_user_points_log');

Using,

SELECT table_name 
FROM test
order by (substring_index(substring_index(table_name, 'wp_', -1), '_', 1) * 1 )  desc ;

Will give the following result:

table_name
wp_9999_wcpv_per_product_shipping_rules
wp_9999_wcpv_commissions
wp_9998_wc_points_rewards_user_points_log
wp_999_woocommerce_log
wp_999_wc_webhooks
wp_999_wc_download_log
wp_999_wcpv_per_product_shipping_rules
wp_999_wcpv_commissions
wp_99_woocommerce_log

https://dbfiddle.uk/590L44Xr

Using substring_index twice we get the number between wp_ and the second _.

* 1 is a shortcut to cast the varchar to int.

In your case it will be something like

SELECT table_name 
FROM information_schema.tables
WHERE table_type = 'base table'
AND table_name REGEXP '^wp_[0-9]+_[a-z0-9]+'
ORDER BY  (substring_index(substring_index(table_name, 'wp_', -1), '_', 1) * 1 )   DESC
LIMIT 1;