如果条件在Oracle SQL中

Question

I am working on a legacy system, and many of the database structures are horrendous (key / value pairs).

I have the following select statement:

(
    SELECT D.F_VALUE
        FROM T_WEB_QUOTES_DATA D
        WHERE
            D.F_QUOTE_ID = TO_CHAR(VR_RENTAL.QUOTEID)
        AND D.F_KEY = 'Secondary_Driver_Forename'
) AS "SECONDARY_DRIVER_FORENAME"

So as you can see it is looking for a record where the F_Key column has a value of Secondary_Driver_Forename . The problem is there is another F_Key that holds the same exact information and I need to check for both keys.

So what I want to do is:

If there are no records where F_Key = Secondary_Driver_Forename or of such a record exists, but the value is an empty string or null, then I would like to go and look for a record where the F_Key is 2ndary_Driver_FirstName and if that does not exist (or is null), I would like to return a string saying No Key

How can I achieve this in Oracle SQL?

Answer 1

I am thinking of something like this:

(
    SELECT (case when max(case when D.F_KEY in 'Secondary_Driver_Forename' then 1 else 0 end) = 1
                 then max(case when D.F_KEY in 'Secondary_Driver_Forename' then D.F_VALUE end)
                 else max(D.F_Value)
            end)
        FROM T_WEB_QUOTES_DATA D
        WHERE
            D.F_QUOTE_ID = TO_CHAR(VR_RENTAL.QUOTEID)
        AND D.F_KEY in ('Secondary_Driver_Forename', '2ndary_Driver_FirstName')
) AS "SECONDARY_DRIVER_FORENAME";

That is, do a conditional aggregation of the values. If the primary value is present, then use it. Otherwise, just choose the value that is there (either NULL or the value from the second key).