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

CHAPTER 12 ■ DATATYPES 505
• BINARY_DOUBLE: This is an IEEE native double-precision floating-point number. On disk
it will consume 9 bytes of storage: 8 fixed bytes for the floating-point number and
1 length byte. It is capable of storing numbers in the range of ~ ± 10 308.25 with 13 digits
of precision.
As you can see from this quick overview, the Oracle NUMBER type has significantly larger
precision than the BINARY_FLOAT and the BINARY_DOUBLE types, but a much smaller range than
the BINARY_DOUBLE. That is, you can store numbers very precisely with many significant digits
in a NUMBER type, but you can store much smaller and larger numbers in the BINARY_FLOAT and
BINARY_DOUBLE types. As a quick example, we can create a table with the various datatypes in
them and see what is stored given the same inputs:
ops$tkyte@ORA10GR1> create table t
2 ( num_col number,
3 float_col binary_float,
4 dbl_col binary_double
5 )
6 /
Table created.
ops$tkyte@ORA10GR1> insert into t ( num_col, float_col, dbl_col )
2 values ( 1234567890.0987654321,
3 1234567890.0987654321,
4 1234567890.0987654321 );
1 row created.
ops$tkyte@ORA10GR1> set numformat 99999999999.99999999999
ops$tkyte@ORA10GR1> select * from t;
NUM_COL FLOAT_COL DBL_COL
------------------------ ------------------------ ------------------------
1234567890.09876543210 1234567940.00000000000 1234567890.09876540000
Note that the NUM_COL returns the exact number we provided as input. There are fewer
than 38 significant digits in the input number (I supplied a number with 20 significant digits),
so the exact number is preserved. The FLOAT_COL, however, using the new BINARY_FLOAT type,
was not able to accurately represent this number. In fact, it preserved only 7 digits accurately.
The DBL_COL faired much better, accurately representing the number in this case out to 17 digits.
Overall, though, this should be a good indication that the BINARY_FLOAT and BINARY_DOUBLE
types will not be appropriate for financial applications! If you play around with different values,
you’ll see different results:
ops$tkyte@ORA10GR1> delete from t;
1 row deleted.
ops$tkyte@ORA10GR1> insert into t ( num_col, float_col, dbl_col )
2 values ( 9999999999.9999999999,
3 9999999999.9999999999,