Teradata中的SQL案例语句

Question

I'm trying to write a simple IF/ELSE statement in Teradata. As far as I understand you have to use a CASE. What I want to do is write a statement that will check if a column IS NOT NULL and display something. ELSE if it IS NULL, display something else.

Every example I found simply replaces a single value with a hard coded string or int. I'm looking for something more along the lines of this which uses the THEN statement to make another SELECT:

  SELECT CARS.VIN_NUM, CARS.DRIVER_NAMES
     CASE
       WHEN CARS.FUEL IS NOT NULL THEN SELECT CARS.DESTINATIONS
       WHEN CARS.FUEL IS NULL THEN SELECT CARS.GAS_STATIONS
     END
  FROM AUTOMOBILES CARS
  WHERE CARS.VIN_NUM IN
  ('345353',
   '354632',
   '535231')
  ORDER BY CARS.VIN_NUM

The end result should be a table displaying the VIN_NUM, DRIVER_NAMES, DESTINATIONS OR GAS_STATIONS based on the CASE. Is something like this possible or am I going about it the wrong way?

Answer 1

If DESTINATIONS and GAS_STATIONS are columns in the table AUTOMOBILES (aliased CARS ) then the following should work:

 SELECT CARS.VIN_NUM, 
        CARS.DRIVER_NAMES,
     CASE
       WHEN CARS.FUEL IS NOT NULL THEN CARS.DESTINATIONS
       ELSE CARS.GAS_STATIONS
     END
  FROM AUTOMOBILES CARS
  WHERE CARS.VIN_NUM IN
  ('345353',
   '354632',
   '535231')
  ORDER BY CARS.VIN_NUM;