Combining 2 columns in sql query based on alternate field

Question

I have 2 columns in a database(sent_time, accept_time) which each include time stamps, as well as a field that can have 2 different values (ref_col). I would like to find a way in my query to make a new column (result_col), which will check the value of ref_col, and copy sent_time if the value is 1, and copy accept_time if the value is 2.

I am using pandas to query the database in python, if that has any bearing on the answer.

Answer 1

When you say "I have 2 columns in a database ", what you actually mean is that you have 2 columns in a table , right?

In sql for postgresql it would be something like:

select (case when ref_col = 1 then sent_time else accept_time end) as result_col
from mytable

don't know how close from SQL standard that is, but would assume it's not that far.

Answer 2

Just use case expression statement :

SELECT sent_time,
       accept_time,
       ref_col,
       CASE WHEN ref_col = 1 THEN sent_col
            ELSE accept_col
        END AS result_col
  FROM Your_Table