[SOLVED] SQL Case Statement selecting data

SQL Case Statement selecting data

I'm working on my first SQL case statement - and unsure how to do this.
I have two different columns of data, one is for drive A, the other drive B.
I want to select data from drive A for display when drive A is active, and display data from drive B when it is active.

I'm having trouble understanding how to use the case statement as a part of the select statement.

I know that the case statement returns a boolean value, but I'm unsure of how to incorporate this into my Select expression. Right now I have:

SELECT t_stamp AS DateTime, 
    CASE WHEN DriveAActive 
         THEN DriveA_TorqueActual 
         ELSE DriveB_TorqueActual

I don't see a good reference on this topic - any pointers?

Solution

Mysql CASE statement is simple and syntax like:

CASE
   WHEN condition_1 THEN result_1
   WHEN condition_2 THEN result_2 
   ... ... ...
   WHEN condition_m THEN result_m
   ELSE result_n
END AS column_name

Your question is not clear. According to question there are two columns DriveA & DriveB. Need to display data which one is 'Active'.

I think DriveA has high priority. So, design code as follows:

  SELECT
      t_stamp AS DateTime, 
      CASE 
          WHEN(DriveA = 'Active')
            THEN DriveA_TorqueActual 
          WHEN(DriveB = 'Active')
            THEN DriveB_TorqueActual
          ELSE NULL
      END AS ACTIVE_DRIVE
  FROM SQL_TABLE

  SELECT
      t_stamp AS DateTime, 
      CASE 
          WHEN(DriveA = 'Active' AND DriveB = 'Active')
            THEN result1
          WHEN(DriveA = 'Active' AND DriveB <> 'Active')
            THEN result2
          WHEN(DriveA <> 'Active' AND DriveB = 'Active')
            THEN result3
          ELSE result4
      END AS ACTIVE_DRIVE
  FROM SQL_TABLE