Mysql funcation

How to create function in mysql many examples 

 DELIMITER $$
CREATE DEFINER=`skyaws`@`%` FUNCTION `calRh1730ForDS`(_data_date DATE,_stationId INTEGER) RETURNS double
BEGIN
 DECLARE RES DOUBLE;
    SELECT ROUND(Hmdt_Avg,1) INTO RES  FROM STATION_DATA  
    WHERE DATE_FORMAT(DATA_DATE,'%Y-%m-%d %H:%i') = concat(_data_date,'17:30')
    AND STATION_ID=_stationId;
    
    RETURN RES;
    
 END$$
DELIMITER ;

DELIMITER $$
CREATE DEFINER=`skyaws`@`%` FUNCTION `getMaxHumidityForCertificate`(dataDate TIMESTAMP,st_id INTEGER, formulaID INTEGER,cid INTEGER) RETURNS double
BEGIN
DECLARE RES DOUBLE;
IF (formulaID = 2) THEN
      SELECT ROUND(MAX(Humidity),2) INTO RES FROM STATION_DATA st,COMPANY_STATION_MAPPING csm WHERE
      st.IS_UPDATED=1 and
      st.STATION_ID = st_id
       AND DATA_DATE>=DATE_FORMAT(dataDate, '%Y-%m-%d 01:00:00')  AND DATA_DATE<=DATE_FORMAT(DATE_ADD(dataDate, INTERVAL 1 DAY), '%Y-%m-%d 00:00:00')
       AND DATE(DATA_DATE)<=DATE(DATA_TO_DATE) AND COMPANY_ID=cid AND csm.STATION_ID=st.STATION_ID;
  ELSE
      SELECT ROUND(MAX(Humidity),2) INTO RES FROM STATION_DATA WHERE
      IS_UPDATED=1 and
      STATION_ID = st_id
       AND DATA_DATE>=DATE_FORMAT(dataDate, '%Y-%m-%d 00:00:00') AND DATA_DATE<=DATE_FORMAT(dataDate, '%Y-%m-%d 23:59:59');
  END IF;
RETURN RES;
   
    END$$
DELIMITER ;

DELIMITER $$
CREATE DEFINER=`skyaws`@`%` FUNCTION `getDirectionByAngle`(angle FLOAT) RETURNS text CHARSET utf8
BEGIN
DECLARE winddirection TEXT; 
  SELECT
   CASE
        WHEN  348.75<angle && angle<360 THEN 'N'
        WHEN  0<=angle  &&  angle<=11.25  THEN 'N'
        WHEN  11.25<angle   &&  angle<=33.75  THEN 'NNE'
        WHEN  33.75<angle   &&  angle<=56.25  THEN 'NE'
        WHEN  56.25<angle   &&  angle<=78.75  THEN 'ENE'
        WHEN  78.75<angle   &&  angle<=101.25 THEN 'E'
        WHEN  101.25<angle  &&  angle<=123.75 THEN 'ESE'
        WHEN  123.75<angle  &&  angle<=146.25 THEN 'SE'
        WHEN  146.25<angle  &&  angle<=168.75 THEN 'SSE'
        WHEN  168.75<angle  &&  angle<=191.25 THEN 'S'
        WHEN  191.25<angle  &&  angle<=213.75 THEN 'SSW'
        WHEN  213.75<angle  &&  angle<=236.25 THEN 'SW'
        WHEN  236.25<angle  &&  angle<=258.75 THEN 'WSW'
        WHEN  258.75<angle  &&  angle<=281.25 THEN 'W'
        WHEN  281.25<angle  &&  angle<=303.75 THEN 'WNW'
        WHEN  303.75<angle  &&  angle<=326.25 THEN 'NW'
        WHEN  326.25<angle  &&  angle<=348.75 THEN 'NNW' 
        ELSE   'N'
    END AS dir INTO winddirection;    
  RETURN winddirection;
END$$
DELIMITER ;

DELIMITER $$
CREATE DEFINER=`root`@`localhost` FUNCTION `getDistanceFromLatlon`(lat1 FLOAT, lon1 FLOAT, lat2 FLOAT, lon2 FLOAT) RETURNS float
BEGIN SET @radi=6371; SET @dlat=RADIANS(lat1-lat2); SET @dlon=RADIANS(lon1-lon2); SET @a=( SIN(@dlat/2) * SIN(@dlat/2) + RADIANS(COS(lat1)) * RADIANS(COS(lat2))  * SIN(@dlon/2) * SIN(@dlon/2) );  SET @c=2*ATAN2(SQRT(@a), SQRT(1-@a)); SET @distance=@radi * @c; RETURN @distance;

END$$
DELIMITER ;

DELIMITER $$
CREATE DEFINER=`skyaws`@`%` FUNCTION `getMaxTempForCertificate`(dataDate TIMESTAMP,st_id INTEGER, formulaID INTEGER,cid INTEGER) RETURNS double
BEGIN
DECLARE RES DOUBLE;
IF (formulaID = 2) THEN
      SELECT ROUND(MAX(PYRANO),2) INTO RES FROM STATION_DATA st,COMPANY_STATION_MAPPING csm WHERE
      st.IS_UPDATED=1 and
      st.STATION_ID = st_id
       AND DATA_DATE>=DATE_FORMAT(dataDate, '%Y-%m-%d 01:00:00')  AND DATA_DATE<=DATE_FORMAT(DATE_ADD(dataDate, INTERVAL 1 DAY), '%Y-%m-%d 00:00:00')
       #AND DATE(DATA_DATE)<=DATE(DATA_TO_DATE)
       AND COMPANY_ID=cid AND csm.STATION_ID=st.STATION_ID;
  ELSE
      SELECT ROUND(MAX(PYRANO),2) INTO RES FROM STATION_DATA WHERE
      IS_UPDATED=1 and
      STATION_ID = st_id
       AND DATA_DATE>=DATE_FORMAT(dataDate, '%Y-%m-%d 00:00:00') AND DATA_DATE<=DATE_FORMAT(dataDate, '%Y-%m-%d 23:59:59');
  END IF;
RETURN RES;
   
    END$$
DELIMITER ;