date_diff Teradata UDF (SQL)

This function will return the difference between two timestamps.
Input parameters are :
Desire Difference (e.g. year, month, day, minute, hour, second)
Start timestamp (e.g. ‘2000-10-18 22:03:07’)
End timestamp(e.g. ‘2018-12-18 08:10:07’)
Syntax:
date_diff(‘year’, TIMESTAMP ‘2000-10-18 22:03:07’, TIMESTAMP ‘2018-12-18 08:10:07’)

REPLACE FUNCTION syslib.date_diff(vDiff VARCHAR(255), StartTimestamp TIMESTAMP, EndTimeStamp TIMESTAMP)
  RETURNS INT
  LANGUAGE SQL
  CONTAINS SQL
  DETERMINISTIC
  SQL SECURITY DEFINER
  COLLATION INVOKER
  INLINE TYPE 1
  RETURN 
      ROUND(
      CASE WHEN UPPER(vDiff) = 'YEAR' THEN
              (EXTRACT(DAY FROM (EndTimeStamp  - StartTimestamp DAY(4) TO SECOND)) / 365)
          WHEN  UPPER(vDiff) = 'MONTH' THEN
              (EXTRACT(DAY FROM (EndTimeStamp  - StartTimestamp DAY(4) TO SECOND)) / 365)*12
          WHEN  UPPER(vDiff) = 'DAY' THEN
              (EXTRACT(DAY FROM (EndTimeStamp  - StartTimestamp DAY(4) TO SECOND)))
          WHEN  UPPER(vDiff) = 'HOUR' THEN
              (EXTRACT(DAY FROM (EndTimeStamp  - StartTimestamp DAY(4) TO SECOND)) * (24))
             + (EXTRACT(HOUR FROM (EndTimeStamp - StartTimestamp DAY(4) TO SECOND)))
          WHEN  UPPER(vDiff) = 'MINUTE' THEN
              (EXTRACT(DAY FROM (EndTimeStamp  - StartTimestamp DAY(4) TO SECOND)) * (24*60))
             + (EXTRACT(HOUR FROM (EndTimeStamp - StartTimestamp DAY(4) TO SECOND)) * 60)
             + (EXTRACT(MINUTE FROM (EndTimeStamp - StartTimestamp DAY(4) TO SECOND)) )
          WHEN  UPPER(vDiff) = 'SECOND' THEN
              (EXTRACT(DAY FROM (EndTimeStamp  - StartTimestamp DAY(4) TO SECOND)) * (246060))
             + (EXTRACT(HOUR FROM (EndTimeStamp - StartTimestamp DAY(4) TO SECOND)) * (60*60))
             + (EXTRACT(MINUTE FROM (EndTimeStamp - StartTimestamp DAY(4) TO SECOND)) * 60)
             + EXTRACT(SECOND FROM (EndTimeStamp - StartTimestamp DAY(4) TO SECOND))
      ELSE -1
      END
     )
     ; 

Testing SQL

WITH tsval AS 
   (
      SELECT TIMESTAMP '2000-10-18 22:03:07' starttime
           , TIMESTAMP '2018-12-18 22:03:07' endtime 
   ),
   dv AS
   (
      SELECT 'YEAR' (VARCHAR(255)) dval FROM (SELECT 1 a) a UNION
      SELECT 'MONTH' (VARCHAR(255)) dval FROM (SELECT 1 a) a UNION
      SELECT 'day' (VARCHAR(255)) dval FROM (SELECT 1 a) a UNION
      SELECT 'hOuR' (VARCHAR(255)) dval FROM (SELECT 1 a) a UNION
      SELECT 'SeCoNd' (VARCHAR(255)) dval FROM (SELECT 1 a) a UNION
      SELECT 'MiNute' (VARCHAR(255)) dval FROM (SELECT 1 a) a  
   )
     SELECT dval , starttime, endtime, syslib.date_diff(dval, starttime, endtime) 
     FROM tsval, dv