Apress.Expert.Oracle.Database.Architecture.9i.and.10g.Programming.Techniques.and.Solutions.Sep.2005

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CHAPTER 12 ■ DATATYPES
MSG
NUM_COL
---------- ----------
123.45 123.45
123.456 123.46
Notice how the number 123.456, with more than five digits, succeeded this time. That is
because the scale we used in this example was used to round 123.456 to two digits, resulting in
123.46, and then 123.46 was validated against the precision, found to fit, and inserted. However,
if we attempt the following insert, it fails:
ops$tkyte@ORA10GR1> insert into t (msg,num_col) values ( '1234', 1234 );
insert into t (msg,num_col) values ( '1234', 1234 )
*
ERROR at line 1:
ORA-01438: value larger than specified precision allows for this column
because the number 1234.00 has more than five digits in total. When you specify the scale of 2,
at most three digits may be to the left of the decimal place and two to the right. Hence, that
number does not fit. The NUMBER(5,2) column can hold all values between 999.99 and –999.99.
It may seem strange to allow the scale to vary from –84 to 127. What purpose could a negative
scale fulfill? It allows you to round values to the left of the decimal place. Just as the
NUMBER(5,2) rounded values to the nearest .01, so a NUMBER(5,-2) would round to the nearest
100, for example:
ops$tkyte@ORA10GR1> create table t ( msg varchar2(10), num_col number(5,-2) );
Table created.
ops$tkyte@ORA10GR1> insert into t (msg,num_col) values ( '123.45', 123.45 );
1 row created.
ops$tkyte@ORA10GR1> insert into t (msg,num_col) values ( '123.456', 123.456 );
1 row created.
ops$tkyte@ORA10GR1> select * from t;
MSG
NUM_COL
---------- ----------
123.45 100
123.456 100
The numbers were rounded up to the nearest 100. We still have five digits of precision, but
there are now seven digits (including the trailing two 0s) permitted to the left of the decimal
point:
ops$tkyte@ORA10GR1> insert into t (msg,num_col) values ( '1234567', 1234567 );
1 row created.
ops$tkyte@ORA10GR1> select * from t;