Is “NUMBER” and “NUMBER(*,0)” the same in Oracle?

问题

In Oracle documentation it is mentioned that

NUMBER (precision, scale)

If a precision is not specified, the column stores values as given. If no scale is specified, the scale is zero.

But NUMBER (without precision and scale) is also accepting floating point numbers (34.30) but according to documentation if scale is not specified it should be zero scale by default so it should allow only integers, am I wrong?.

And in another questions it is mentioned that

default precision is 38, default scale is zero

So NUMBER and NUMBER(*,0) should be equal but they are not.

Where am I wrong?

回答1:

The default of scale is not zero, which has no value in it. Hence it can accept any value between -84 to 127. If you limit it to zero then it will not accept any presicion even the value contains the scale value

create table aaaaa
(
sno number(*,0),
sno1 number
);

The user_tab_columns will give you the value of your precision and scale

SQL> select column_name,data_precision,data_scale from user_tab_columns where ta
ble_name = 'AAAAA';

COLUMN_NAME                    DATA_PRECISION DATA_SCALE
------------------------------ -------------- ----------
SNO                                                    0
SNO1

SQL>

Please find the below workings

SQL> select * from aaaaa;

no rows selected

SQL> insert into aaaaa values (123.123123,123123.21344);

1 row created.

SQL> commit;

Commit complete.

SQL> select * from aaaaa;

       SNO       SNO1
---------- ----------
       123 123123.213

SQL>

回答2:

I think the sentence in the documentation

If a precision is not specified, the column stores values as given. If no scale is specified, the scale is zero.

is a bit confusing. The scale is zero if a precision is specified and a scale is not specified. So, for example, NUMBER(19) is equivalent to NUMBER(19,0). NUMBER, by itself, will have 38 digits of precision but no defined scale. So a column defined as a NUMBER can accept values of any scale, as long as their precision is 38 digits or less (basically, 38 numerical digits with a decimal point in any place).

You can also specify a scale without a precision: NUMBER(*, <scale>), but that just creates the column with 38 digits of precision so I'm not sure it's particularly useful.

The table How Scale Factors Affect Numeric Data Storage on this page might be helpful.

回答3:

This parts of Oracle documentation makes it absolutely clear:

Specify an integer using the following form:

NUMBER(p)

This represents a fixed-point number with precision p and scale 0 and is equivalent to NUMBER(p,0).

and

Specify a floating-point number using the following form:

NUMBER

The absence of precision and scale designators specifies the maximum range and precision for an Oracle number.

The meaning of the star precision is documented here and means the precision of 38

来源：https://stackoverflow.com/questions/28207708/is-number-and-number-0-the-same-in-oracle