Draft of a function that returns the first weekday of a month

first_week_day.sql

DROP FUNCTION first_week_day;
DELIMITER //
CREATE FUNCTION first_week_day (year INT,  month INT, weekday_index INT)
    RETURNS VARCHAR(10)
    DETERMINISTIC
    BEGIN
       DECLARE day_number INT DEFAULT 1;
       DECLARE date_string VARCHAR(10); 
       SET date_string = CONCAT(convert(year, char), "-", convert(month, char), "-", convert(day_number, char));
       return date_string;
	END
//

SELECT STR_TO_DATE(first_week_day(2015, 29, 0), '%d/%m/%Y');