INSERT INTO `table_name` (`language`, `image_path`, `page_content`, `ID`)
VALUES (
language_in,
image_path_in,
page_content_in,
CASE
WHEN exists(SELECT 1 from `table_name` where image_path = image_path_in) then
((select `ID` from `table_name` where image_path = image_path_in))
ELSE
((select max(`ID`) + 1 from `table_name`))
END
);