If..then..else statement in SQL with 'generalized' conditions in the if sta

Question

it is possible to write something approaching an if..then..else statement in SQL with 'generalized' conditions in the if statement.
Attached is the query for the payment register, in which I've written a series of decode statements, one for each possible value of the payment code. The query works OK - however, its specific and as the number of paycodes expand (and they do), the report won't pick up the new paycode until the code is changed. More importantly, the report won't be correct until someone 'discovers' that a paycode is missing, which might take months.
If I were writing the equivalent of this series of decode statements in Focus, it would be something like this:
DEFINE.......
PAYMED/D12.2 = IF PAYMENT_CD LE 18
               THEN PAYMENT_AMT
               ELSE 0 ;
PAYIND/D12.2 = IF PAYMENT_CD GE 19 AND PAYMENT_CD LE 49
               THEN PAYMENT_AMT
               ELSE 0 ;
PAYEXP/D12.2 = IF PAYMENT_CD GE 70
               THEN PAYMENT_AMT
               ELSE 0 ;
PAYREC/D12.2 = IF PAYMENT_CD GE 50 AND PAYMENT_CD LE 69
               THEN PAYMENT_AMT
               ELSE 0;
END
IN SQL/PLUS:
SELECT ACCOUNT_NAME,
LOCATION_1,
CLMNT_LAST_NAME,
CLAIM_NBR,
DATE_OF_INJURY,
DATE_CHECK_REGISTER,
PAYEE_NAME_1,
PAYMENT_CD,
SERV_OFC,
CPO_CHECK_NBR,
PAYMENT_FORM,
DECODE(PAYMENT_CD, 20, PAYMENT_AMT, 21, PAYMENT_AMT,
22, PAYMENT_AMT, 23, PAYMENT_AMT, 25, PAYMENT_AMT,
26, PAYMENT_AMT, 27, PAYMENT_AMT, 28, PAYMENT_AMT,
29, PAYMENT_AMT, 30, PAYMENT_AMT, 31, PAYMENT_AMT,
32, PAYMENT_AMT, 33, PAYMENT_AMT, 34, PAYMENT_AMT,
35, PAYMENT_AMT, 36, PAYMENT_AMT, 37, PAYMENT_AMT,
39, PAYMENT_AMT, 40, PAYMENT_AMT, 41, PAYMENT_AMT,
42, PAYMENT_AMT, 43, PAYMENT_AMT, 44, PAYMENT_AMT,
45, PAYMENT_AMT, 46, PAYMENT_AMT, 47, PAYMENT_AMT,
48, PAYMENT_AMT, 49, PAYMENT_AMT, NULL) INDEMNITY,
DECODE(PAYMENT_CD, 0, PAYMENT_AMT, 1, PAYMENT_AMT,
2, PAYMENT_AMT, 3, PAYMENT_AMT, 4, PAYMENT_AMT,
5, PAYMENT_AMT, 6, PAYMENT_AMT, 7, PAYMENT_AMT,
8, PAYMENT_AMT, 9, PAYMENT_AMT, 10, PAYMENT_AMT,
11, PAYMENT_AMT, 12, PAYMENT_AMT, 13, PAYMENT_AMT,
14, PAYMENT_AMT, 15, PAYMENT_AMT, 18, PAYMENT_AMT,
17, PAYMENT_AMT, NULL) MEDICAL,
DECODE(PAYMENT_CD, 70, PAYMENT_AMT, 71, PAYMENT_AMT,
72, PAYMENT_AMT, 73, PAYMENT_AMT, 74, PAYMENT_AMT,
75, PAYMENT_AMT, 76, PAYMENT_AMT, 77, PAYMENT_AMT,
78, PAYMENT_AMT, 79, PAYMENT_AMT, 80, PAYMENT_AMT,
81, PAYMENT_AMT, 82, PAYMENT_AMT, 83, PAYMENT_AMT,
84, PAYMENT_AMT, 85, PAYMENT_AMT, 86, PAYMENT_AMT,
87, PAYMENT_AMT, 88, PAYMENT_AMT, 89, PAYMENT_AMT,
90, PAYMENT_AMT, NULL) EXPENSES,
DECODE(PAYMENT_CD, 50, PAYMENT_AMT, 51, PAYMENT_AMT,
52, PAYMENT_AMT, 53, PAYMENT_AMT, 54, PAYMENT_AMT,
55, PAYMENT_AMT, 56, PAYMENT_AMT, 57, PAYMENT_AMT,
58, PAYMENT_AMT, NULL) RECOVERIES,
DECODE(PAYMENT_FORM, 'N', PAYMENT_AMT, NULL) NONCASH,
DATE_FROM_SERVICE,
DATE_THRU_SERVICE
FROM &INPUT_TABLES
WHERE &SECURITYCOND
DATE_OF_PAYMENT BETWEEN :START_DATE AND :END_DATE
ORDER BY LOCATION_1, CPO_CHECK_NBR
As you can see, this is both much easier to write and covers the possibility of expansion of paycodes (expansions always fit in these defined ranges).
My question is, then, is it possible to write something like this in SQL and, if so, could you give me some sample code? (I'm one of those people who learn best from looking at the code as opposed to a set of instructions)

Answer 1

Here is one way you could do it.
Create a table that has columns like:
Payment_code varchar2(2),
Effective_Date Date,
Payment_type varchar2(20),
Expiration_Date Date)
Payment type for example could be
I- indemnity
M- medical
R- recovery
E- expenses
Let the table name for example be PAYMENT_CODE.
The select query would look like
SELECT ACCOUNT_NAME,
LOCATION_1,
CLMNT_LAST_NAME,
CLAIM_NBR,
DATE_OF_INJURY,
DATE_CHECK_REGISTER,
PAYEE_NAME_1,
PAYMENT_CD,
SERV_OFC,
CPO_CHECK_NBR,
PAYMENT_FORM,
DECODE(p.payment_type,'E',PAYMENT_AMOUNT,0) expenses,
DECODE(p.payment_type,'I',PAYMENT_AMOUNT,0) indemnity,
DECODE(p.payment_type,'M',PAYMENT_AMOUNT,0) Medical,
DECODE(p.payment_type,'R',PAYMENT_AMOUNT,0) recoveries,
DECODE(PAYMENT_FORM, 'N', PAYMENT_AMT, NULL) NONCASH
FROM &INPUT_TABLES,
PAYMENT_CODE P
WHERE P.PAYMENT_CODE = SOMEINPUT_TABLE.PAYMENT_CODE
and other conditions
The idea is to group all the payment codes into a few groups to reduce the clutter. If there is ever a change to the payment code, you could modify the table and it will be reflected in your select query.