Strange decode or just Strange Day (for me)

Question

Hi,
Why does this work:
SQL> ed
Wrote file afiedt.buf
1 declare
2 p_cont varchar2(1) := 'C';
3 v_x VARCHAR2(1) := NULL;
4 CURSOR chek_p_cont
5 IS
6 SELECT 'X'
7 FROM dual
8 WHERE p_cont = DECODE (
9 p_cont, 'A'--,'A'
10 , p_cont, 'B'--,'B'
11 , p_cont, 'C'--,'C'
12 , p_cont, 'D'--,'D'
13 , p_cont, 'E'--,'E'
14 );
15 begin
16 open chek_p_cont;
17 FETCH chek_p_cont
18 INTO v_x;
19 if ( chek_p_cont%FOUND ) THEN dbms_output.put_line('trus');
20 end if;
21* end;
SQL> /
trus
PL/SQL procedure successfully completed.
SQL>
And this does not:
SQL> l
1 declare
2 p_cont varchar2(1) := 'C';
3 v_x VARCHAR2(1) := NULL;
4 CURSOR chek_p_cont
5 IS
6 SELECT 'X'
7 FROM dual
8 WHERE p_cont = DECODE (
9 p_cont, 'A','A'
10 , p_cont, 'B','B'
11 , p_cont, 'C','C'
12 , p_cont, 'D','D'
13 , p_cont, 'E','E'
14 );
15 begin
16 open chek_p_cont;
17 FETCH chek_p_cont
18 INTO v_x;
19 if ( chek_p_cont%FOUND ) THEN dbms_output.put_line('trus');
20 end if;
21* end;
SQL> /
PL/SQL procedure successfully completed.
SQL>
Am i missing something here guys .
thanks
n.

Answer 1

In the first Decode you are saying
IF p_cont = 'A' then return p_cont
ELSIF p_cont = 'B' then return p_cont
ELSIF p_cont = 'C' then return p_cont
ELSIF p_cont = 'D' then return p_cont
ELSIF p_cont = 'E' then return p_cont
END IF;
In the second I'm not sure what you are trying to say. But it does not make sense. Here is some of it
IF p_cont = 'A' then return 'A'
elsif p_cont = p_cont then return 'B'
The DECODE works as follows
Decode( p_val ,
              'A' , 'ONE'
              'B' , 'TWO',
              'NONE' ) ;IF p_val = 'A' then 'ONE'
elsif p_val = 'B' then 'TWO'
else 'NONE'
end if;
If only takes one parameter and does the compare(s) and returns a value. To test what will be returned from the decode put it as a column in the query.