Decode statement with ||','||

Question

Hi ,
I've the following requriement where i need to append the 2 numbers with comma inside the decode stmt
create table  A_STY_VON ( C_1_ID number ,C_2_ID number ,C_3_ID number)
Insert into A_STY_VON
   (C_1_ID, C_2_ID, C_3_ID)
Values
   (1, 2, 3);
Insert into A_STY_VON
   (C_1_ID, C_3_ID)
Values
   (1, 3);
Insert into A_STY_VON
   (C_1_ID, C_2_ID)
Values
   (1, 2);
Insert into A_STY_VON
   (C_2_ID, C_3_ID)
Values
   (2, 3);And the following select stmt is working
SELECT   DECODE (
          A.C_3_ID,
          NULL, DECODE (A.C_2_ID,
                        NULL, A.C_1_ID,
                        A.C_1_ID || A.C_2_ID) ,
             A.C_1_ID
         || A.C_2_ID
         || A.C_3_Id) dcd
  FROM A_STY_VON A But i want the comma between the numbers so i tried the following ( with distinct )
where i'm getting the invalid number error
SELECT  distinct DECODE (
          A.C_3_ID,
          NULL, DECODE (A.C_2_ID,
                        NULL, A.C_1_ID,
                        A.C_1_ID ||','|| A.C_2_ID) ,
             A.C_1_ID
          ||','|| A.C_2_ID
          ||','|| A.C_3_Id) dcd
  FROM A_STY_VON A Could you please help me to achieve this
Thank you
Edited by: Smile on Apr 26, 2012 3:50 AM

Answer 1

Just so you can understand why the problem has happened...
There are some implicit datatype conversions going on in your statement, let's just look at a small part of it...
DECODE (A.C_2_ID,
                        NULL, A.C_1_ID,
                        A.C_1_ID || A.C_2_ID)Your ID's are numeric.
DECODE as a function can only return a single datatype. That datatype is determined by the datatype of the first value to be returned (if it's null that's another issue but let's not go there).
So, in your above statement the datatype returned by DECODE is determined by A.C_1_ID, which is numeric.
Also in your above statement you are doing a string concatenation of A.C_1_ID and A.C_2_ID, so those numbers are implicitly converted to strings and concatenated, but then because DECODE is now defined as needing a number to be returned, the concatenated string of numbers are implicitly converted back to a number, which is fine because the whole string is numeric.
In PL/SQL code this would go along these principles...
... function ...
declare
  v_retval NUMBER;
  v_c_1_id NUMBER := 123;
  v_c_2_id NUMBER := 234;
begin
  if v_c_2_id is null then
    v_retval := v_c_1_id;
  else
    v_retval := to_number(to_char(v_c_1_id)||to_char(v_c_2_id));
  end if;
  return v_retval;
end;Now, if you try and put a comma into your concatenation...
DECODE (A.C_2_ID,
                        NULL, A.C_1_ID,
                        A.C_1_ID ||','|| A.C_2_ID)Still the first value returned has defined the DECODE as needing to return a numeric value, but this time the second returned value (The 'else' part of the decode) has a string containing numeric digits with a comma in between. When it implicitly tries to convert this string to a number so it can be returned from the function, it finds that it's not a valid number.
And we can see this if we use the same PL/SQL type code...
SQL> declare
  2    v_retval NUMBER;
  3    v_c_1_id NUMBER := 123;
  4    v_c_2_id NUMBER := 234;
  5  begin
  6    if v_c_2_id is null then
  7      v_retval := v_c_1_id;
  8    else
  9      v_retval := to_number(to_char(v_c_1_id)||','||to_char(v_c_2_id));
10    end if;
11    --return v_retval;
12  end;
13  /
declare
ERROR at line 1:
ORA-06502: PL/SQL: numeric or value error: character to number conversion error
ORA-06512: at line 9It can't do the to_number on the string when it expects the return value to be numeric.
SQL has a nice NVL2 function (http://docs.oracle.com/cd/B19306_01/server.102/b14200/functions106.htm) which you can use instead when trying to determine different output based on one of the values being null...
SQL> ed
Wrote file afiedt.buf
  1  with a as (select 123 as c_1_id, 234 as c_2_id from dual union all
  2             select 789, null from dual)
  3  --
  4  -- end of test data
  5  --
  6  select c_1_id, c_2_id,
  7         nvl2(c_2_id,c_1_id||','||c_2_id,c_1_id) as result
  8* from a
SQL> /
    C_1_ID     C_2_ID RESULT
       123        234 123,234
       789            789Again, this is using implicit datatype conversion and the resultant datatype of NVL2 is determined by the first result (the second parameter) just as with decode, but because of the way it works, the first result is what it should do if the passed in first parameter is not null and therefore you can force the implicit conversion to a string datatype that way.