Question

is there a way to apply a query to each table in a mysql database?

Something like

SELECT count(*) FROM {ALL TABLES}
-- gives the number of count(*) in each Table

and

DELETE FROM {ALL TABLES}
-- Like DELETE FROM TABLE applied on each Table

Answer 1

select sum(table_rows) as total_rows
from information_schema.tables
where table_schema = 'your_db_name'

beware this is just an approximate value

In order to delete the contents of all your tables you can do something like this

select concat('truncate ',table_name,';')
from information_schema.tables
where table_schema = 'your_db_name'

Then run the output of this query.

UPDATE.

This is a stored procedure to apply truncate table to all tables in a specific database

delimiter //
drop procedure if exists delete_contents //
create procedure delete_contents (in db_name varchar(100))
begin
declare finish int default 0;
declare tab varchar(100);
declare cur_tables cursor for select table_name from information_schema.tables where table_schema = db_name and table_type = 'base table';
declare continue handler for not found set finish = 1;
open cur_tables;
my_loop:loop
fetch cur_tables into tab;
if finish = 1 then
leave my_loop;
end if;

set @str = concat('truncate ', tab);
prepare stmt from @str;
execute stmt;
deallocate prepare stmt;
end loop;
close cur_tables;
end; //
delimiter ;

call delete_contents('your_db_name');