Conditional columns query

Question

hi
Iam trying to write a query which is as follows
select A1,A2,A3,A4,A5,A5,A6,A7 from table.
such that columns A1,A2,A3 must be displayed only when A1 is not null
and columns A4,A5,A6 must be displayed only when A4 is not null.
any help..
thanks
Kumar

Answer 1

Alternatively:
SELECT NVL2(a1, a1, NULL) a1, NVL2(a1, a2, NULL) a2, NVL2(a1, a3, NULL) a3,
       NVL2(a4, a4, NULL) a4, NVL2(a4, a5, NULL) a5, NVL2(a4, a6, NULL) a6
FROM <table_name>;NVL2 demos here:
http://www.morganslibrary.org/reference/misc_func.html#mfn2
SQL> create table test1 (
  2  a1 number,
  3  a2 number,
  4  a3 number,
  5  a4 number,
  6  a5 number,
  7  a6 number);
Table created.
SQL> insert into test1 values (NULL,1,1,1,1,1);
1 row created.
SQL> insert into test1 values (1,1,1,NULL,1,1);
1 row created.
SQL> insert into test1 values(1,1,1,1,1,1);
1 row created.
SQL> set timing on
SQL> DECLARE
  2  CURSOR casecur IS
  3  SELECT  (CASE WHEN A1 IS NOT NULL THEN A1 END) AS A1
  4  ,       (CASE WHEN A1 IS NOT NULL THEN A2 END) AS A2
  5  ,       (CASE WHEN A1 IS NOT NULL THEN A3 END) AS A3
  6  ,       (CASE WHEN A2 IS NOT NULL THEN A4 END) AS A4
  7  ,       (CASE WHEN A2 IS NOT NULL THEN A5 END) AS A5
  8  ,       (CASE WHEN A2 IS NOT NULL THEN A6 END) AS A6
  9  FROM test1;
10  BEGIN
11    FOR i IN 1 .. 100000 LOOP
12      FOR caserec IN casecur LOOP
13        NULL;
14      END LOOP;
15    END LOOP;
16  END;
17  /
PL/SQL procedure successfully completed.
Elapsed: 00:00:06.67
SQL> DECLARE
  2  CURSOR casecur IS
  3  SELECT NVL2(a1, a1, NULL) a1, NVL2(a1, a2, NULL) a2, NVL2(a1, a3, NULL) a3,
  4         NVL2(a4, a4, NULL) a4, NVL2(a4, a5, NULL) a5, NVL2(a4, a6, NULL) a6
  5  FROM test1;
  6  BEGIN
  7    FOR i IN 1 .. 100000 LOOP
  8      FOR caserec IN casecur LOOP
  9        NULL;
10      END LOOP;
11    END LOOP;
12  END;
13  /
PL/SQL procedure successfully completed.
Elapsed: 00:00:06.62
SQL> I don't think it is going to much matter which you choose.