SELECT with default result for empty condition?

Question

I have a database table with following fields and values:

Bukrs | Werks | Btrtl | Persg | Persk | value
1000   1000     1001     1      20      1,20
1000                                    1,10

And I am building the query with the following key:

SELECT
FROM dbtab
INTO lv_value
WHERE bukrs = bukrs
    AND (
        werks = werks
        AND btrtl = btrtl
        AND persg = persg
        AND persk = persk
        )

So for query with the exact condition condition match the value must be 1,20, and that is correct.

But for another condition without full match e.g. bukrs = 1000 werks = 1002 btrtl = 1003 persg = 2 persk = 27, it must be 1,10.

So everything which doesn't fit full key should fallback to default line with value 1,10. For example:

Andrew has the following Parameters

Bukrs = 1000
Werks = 1000 
Btrtl = 1001
Persg = 1
Persk = 20

Peter has the following Parameters

Bukrs = 1000
Werks = 1004
Btrtl = 1002
Persg = 1
Persk = 27

For Andrew 1,20 should be selected, for Peter it should be 1,10.

Answer 1

Try this way:

DATA: Andrew TYPE dbtab.

Andrew-bukrs = '1000'.
Andrew-werks = '1000'.
Andrew-btrtl = '1001'.
Andrew-persg = '1'.
Andrew-persk = '20'.

SELECT SINGLE value INTO @DATA(Andy) 
  FROM dbtab WHERE werks = ANY ( SELECT CASE WHEN bukrs = @Andrew-bukrs 
                                              AND werks = @Andrew-werks 
                                              AND btrtl = @Andrew-btrtl
                                              AND persg = @Andrew-persg 
                                              AND persk = @Andrew-persk
                                        THEN werks 
                                        ELSE '9999' 
                                 END AS werks FROM dbtab 
                               ).

WRITE / Andy-value.

This snippet gives you 1.20, and the same query for the person with only BUKRS gives you 1.10.

DATA: Peter TYPE dbtab.

Peter-bukrs = '1000'.

SELECT ....

Explanation: here we simulate XOR operator for ABAP SQL through the subqueries. Our subquery always returns two values: only one truthful row from dbtab table, the other one is always a dummy 9999. This way the outer query will always return single value by the plant, either real or dummy.

Prerequisite for this solution: 9999 (subquery plant) must be invariably non-existent in dbtab.