Empty row using decode

Question

when I use the decode function I always get extra empty rows in my results. Why is this? Is it because I don't use a default value?
I always have to use a where statement to eliminate those empty rows, like in the following statement.
select
decode(table.field1,'field1value','output')
from
table
where
table.field1='field1value'

Answer 1

Let me try to explain using your example:
SQL> create table mytable
  2  as
  3  select 'Weight' field1, '2' field2 from dual union all
  4  select 'Colour', 'red' from dual union all
  5  select 'Size', 'L' from dual
  6  /
Tabel is aangemaakt.So, the table has three rows.
SQL> select decode(Field1,'Weight',Field2)
  2    from mytable
  3  /
DEC
2
3 rijen zijn geselecteerd.Since you don't have a where clause, you don't restrict the number of rows returned. The row appears empty because of the decode function, which says: "if field1 is equal to 'Weight' then display field2 else display nothing".
SQL> select field1
  2       , field2
  3       , decode(Field1,'Weight',Field2)
  4       , decode(Field1,'Weight',Field2, field1)
  5    from mytable
  6  /
FIELD1 FIE DEC DECODE
Weight 2   2   2
Colour red     Colour
Size   L       Size
3 rijen zijn geselecteerd.This shows that the rows are not empty, only the third column is. The fourth column is a similar decode function but with a fourth argument that additionally says "if field1 is not equal to 'Weight' then show me field1 instead of field2"
But I guess you really want one row, the row containing 'Weight', which can be easily achieved by a where clause:
SQL> select field2
  2    from mytable
  3   where field1 = 'Weight'
  4  /
FIE
2
1 rij is geselecteerd.Hope this clarifies.
Regards,
Rob.