I can’t separate the array by commas

implode(",", [500,756]) will definitely return "500,756", therefore you have some other problem.

If the field type of the ‘num’ field is a numeric type such as MySQL’s INT, then MySQL or PHP might try and convert this string to a number and so "500,756" could become 500.

Check the data type of the ‘num’ field in the ‘number’ table. To store the string you want to store it needs to be a string type such as VARCHAR. Or if you’re trying to store a number with stuff after the decimal point make sure it’s e.g. a FLOAT / DECIMAL, etc. and add the value using a decimal point, e.g. 500.756.

If you need further help, show the CREATE TABLE output for your table