[Oracle 8i] Handling null in case statement

Question

The following bit of my query is causing the error 'inconsistent datatypes':
CASE
     WHEN b.days_diff < 0
     THEN plan_start
     ELSE plan_start + b.days_diff
ENDThe problem is that b.days_diff can be null.
I've tried to work around this, by using the NVL statement and by nesting 2 case statements to try to deal with the null, but can't seem to work around it.
Does anyone have anything else I can try?

Answer 1

Apologies...internet server went down yesterday...
I've had this issue before with my database. When I look at user_tab_columns, it says plan_start is a date. However, I have had to use TO_DATE in the past with it to get some things to work. It's very odd, and I have no idea why it's like that.
Anyway, below, I have provided some sample data, and the full query I'm trying to run:
CREATE TABLE     ord (
ord_nbr          char(10)
ord_stat     char(2)
INSERT INTO     ord
VALUES          ('0000012345', 'OP');
INSERT INTO     ord
VALUES          ('0000012346', 'OP');
INSERT INTO     ord
VALUES          ('0000012347', 'CL');
INSERT INTO     ord
VALUES          ('0000012348', 'OP');
CREATE TABLE     op (
ord_nbr          char(10)
operation     char(4)
op_status     char(2)
plan_start     date
pln_due          date
dt_complete     date
INSERT INTO     op
VALUES          ('0000012345', '0001', 'CL', {ts '2009-01-01 00:00:00'}, {ts '2009-01-02 00:00:00'}, {ts '2009-01-04 00:00:00'});
INSERT INTO     op
VALUES          ('0000012345', '0002', 'CL', {ts '2009-01-02 00:00:00'}, {ts '2009-01-03 00:00:00'}, {ts '2009-01-06 00:00:00'});
INSERT INTO     op
VALUES          ('0000012345', '0003', 'CL', {ts '2009-01-03 00:00:00'}, {ts '2009-01-04 00:00:00'}, {ts '2009-01-09 00:00:00'});
INSERT INTO     op
VALUES          ('0000012345', '0004', 'WK', {ts '2009-01-04 00:00:00'}, {ts '2009-01-05 00:00:00'}, {ts '1900-12-31 00:00:00'});
INSERT INTO     op
VALUES          ('0000012345', '0005', 'OP', {ts '2009-01-05 00:00:00'}, {ts '2009-01-06 00:00:00'}, {ts '2009-01-02 00:00:00'});
INSERT INTO     op
VALUES          ('0000012346', '0001', 'CL', {ts '2009-01-01 00:00:00'}, {ts '2009-01-02 00:00:00'}, {ts '2009-01-01 00:00:00'});
INSERT INTO     op
VALUES          ('0000012346', '0002', 'OP', {ts '2009-01-02 00:00:00'}, {ts '2009-01-04 00:00:00'}, {ts '1900-12-31 00:00:00'});
INSERT INTO     op
VALUES          ('0000012346', '0003', 'OP', {ts '2009-01-04 00:00:00'}, {ts '2009-01-06 00:00:00'}, {ts '1900-12-31 00:00:00'});
INSERT INTO     op
VALUES          ('0000012347', '0001', 'CL', {ts '2009-01-01 00:00:00'}, {ts '2009-01-02 00:00:00'}, {ts '2009-01-03 00:00:00'});
INSERT INTO     op
VALUES          ('0000012347', '0002', 'CL', {ts '2009-01-02 00:00:00'}, {ts '2009-01-05 00:00:00'}, {ts '2009-01-06 00:00:00'});
INSERT INTO     op
VALUES          ('0000012348', '0001', 'OP', {ts '2009-01-15 00:00:00'}, {ts '2009-01-17 00:00:00'}, {ts '1900-12-31 00:00:00'});
INSERT INTO     op
VALUES          ('0000012348', '0002', 'OP', {ts '2009-01-17 00:00:00'}, {ts '2009-01-20 00:00:00'}, {ts '1900-12-31 00:00:00'});Full query:
SELECT     ord.ord_nbr
,     ord.ord_stat
,     op.operation
,     op.op_status
,     op.plan_start
,     //where I want to return plan_start + days_diff if days_diff is not null or negative
     //otherwise, I want to return just plan_start
     AS adjusted_start
,     op.dt_complete
,     b.max_cl_op
,     b.pln_due
,     b.dt_complete
,     b.days_diff
FROM     ord
,     op
     SELECT     a.ord_nbr
     ,     a.max_cl_op
     ,     op.pln_due
     ,     op.dt_complete
     ,     (op.dt_complete-op.pln_due)     AS days_diff
     FROM     (
          SELECT          op.ord_nbr
          ,          MAX(TO_NUMBER(op.operation))     AS max_cl_op
          FROM          ord
          ,          op
          WHERE          ord.ord_nbr     = op.ord_nbr
          AND          ord.ord_stat     != 'CL'
          AND          op.op_status     ='CL'
          GROUP BY     op.ord_nbr
          ) a
     WHERE     op.ord_nbr     = a.ord_nbr
     AND     op.operation     = a.max_cl_op
     ) b
WHERE     ord.ord_nbr     = op.ord_nbr
AND     op.ord_nbr     = b.ord_nbr (+)
AND     ord.ord_stat     != 'CL'
AND     op.op_status     != 'CL'
AND     op.plan_start     <= ADD_MONTHS(sysdate, 12)The results I want to get:
ord.ord_nbr     ord.ord_stat     op.operation     op.op_status     op.plan_start     adjusted_start     op.dt_complete     b.max_cl_op     b.pln_due     b.dt_complete     b.days_diff
'0000012345'     'OP'          '0004'          'WK'          1/4/2009     1/9/2009     12/31/1900     '0003'          1/4/2009     1/9/2009     5     
'0000012345'     'OP'          '0005'          'OP'          1/5/2009     1/10/2009     12/31/1900     '0003'          1/4/2009     1/9/2009     5
'0000012346'     'OP'          '0002'          'OP'          1/2/2009     1/2/2009     12/31/1900     '0001'          1/2/2009     1/1/2009     -1
'0000012346'     'OP'          '0003'          'OP'          1/4/2009     1/4/2009     12/31/1900     '0001'          1/2/2009     1/1/2009     -1
'0000012348'     'OP'          '0001'          'OP'          1/15/2009     1/15/2009     12/31/1900                                   
'0000012348'     'OP'          '0002'          'OP'          1/17/2009     1/17/2009     12/31/1900