-- Count entries in database
SELECT count(*);

-- Count rows in table
SELECT count(*) FROM peoples;
-- returns the number of rows in this table

-- Count rows with filter
SELECT count(*) FROM peoples WHERE age = 20;
-- returns the number of rows/peoples with an age of 20

-- If none (matching) row is in the specified
-- table it will return 0. So you can
-- check for "if (SQL_return >= 1)"