Different databases have different functions. Take oracle as an example: Common functions of single-sentence function: destinct (removing duplicate lines), to_char (converting from character string), to_date (date format function), sumstr (intercepting from character string), lower (converting letters to lowercase), upper (converting letters to lowercase) and char (converting numbers).

Grouping functions: min (minimum value), max (maximum value), avg (average value), sum (sum) and counnt record;