What the difference between declaring a column using datatype 

number 
and 
number(n)? 

Ay advantage or disadvantge declaring one way and the another? 

Tom Kyte
Followup  

June 30, 2003 - 7:50 am UTC 

number(n) is a number with a constraint and edit.

ops$tkyte@ORA920>; create table t ( x number, y number(5) );

Table created.

ops$tkyte@ORA920>;
ops$tkyte@ORA920>; insert into t values ( 123.456, 123.456 );

1 row created.

ops$tkyte@ORA920>; insert into t values ( 123.999, 123.999 );

1 row created.

ops$tkyte@ORA920>; insert into t values ( 12345, 12345 );

1 row created.

ops$tkyte@ORA920>; insert into t values ( 123456, 123456 );
insert into t values ( 123456, 123456 )
                               *
ERROR at line 1:
ORA-01438: value larger than specified precision allows for this column


ops$tkyte@ORA920>; select * from t;

         X          Y
---------- ----------
   123.456        123
   123.999        124
     12345      12345


See how the number(5) behaves?  5 digits, no decimals, rounded.  

The advantage is 

a) you have 5 digits only, never more
b) you have no decimals, it is an integer type

consider it a constraint -- like a primary key, NOT NULL, check, whatever.  
If your data is such that the number should never be more then 5 digits, the only correct way to implement it would be as a number(5)