How to ensure result of null will default to datatype of column

Question

I have a question
suppose i have two tables with customers and Sales transactions
create SalesTransactionTBL
customerID
,itemID
,itemQuanity
,itemPrice
,orderDateTime
create customerTbl
customerID
customerName
Some customers have bought something as found in SalesTransactionTBL,
some just registered and hand't brought anything and not found in SalesTransactionTBL
If I left join two tables based on customerID, i will get null on many of the fields from SalesTransactionTbl
select *
from customerTbl c
left join SalesTransactionTBL s
on c.CustomerID =s.CustomerID
what is the way to ensure the result of the null value will default to something based on the data type of the column?

Answer 1

What do you mean by ...
+what is the way to ensure the result of the null value will
default to something based on the data type of the column?+
Can you please describe / elaborate?
Why do you want to ensure this?
In Oracle, null value does not have a specific data type.
The data type of columns themself will (by default) will be based on data type of columns from base tables.
sudhakar@ORCL>drop table t1;
Table dropped.
sudhakar@ORCL>create table t1 (c1 int , s1 varchar2(20), d1 date);
Table created.
sudhakar@ORCL>drop table t2;
drop table t2
ERROR at line 1:
ORA-00942: table or view does not exist
sudhakar@ORCL>create table t2 (c2 int , s2 varchar2(20), d2 date);
Table created.
sudhakar@ORCL>
sudhakar@ORCL>insert into t1 values(1,'AAA',sysdate-3);
1 row created.
sudhakar@ORCL>insert into t1 values(2,'BBB',sysdate-2);
1 row created.
sudhakar@ORCL>commit;
Commit complete.
sudhakar@ORCL>select * from t1,t2
  2  where c1 = c2(+);
        C1 S1                   D1                C2 S2                   D2
         1 AAA                  06-MAY-10
         2 BBB                  07-MAY-10
sudhakar@ORCL>create view v1 as
  2  select * from t1,t2
  3  where c1 = c2(+);
View created.
sudhakar@ORCL>desc v1
Name                                                  Null?    Type
C1                                                             NUMBER(38)
S1                                                             VARCHAR2(20)
D1                                                             DATE
C2                                                             NUMBER(38)
S2                                                             VARCHAR2(20)
D2                                                             DATE
sudhakar@ORCL>