Question

Is there any benefit to specifying the precision on the PK? Is 7,0 sufficient, given that there will probably never be more than a few thousand records?

Any dangers to not specifying the precision?

Answer 1

NUMBER(7, 0) just constrains the domain of values.

Their internal represenations do not differ:

CREATE TABLE t_pk (col1 NUMBER(7, 0) NOT NULL, col2 NUMBER(38) NOT NULL)

INSERT
INTO    t_pk
VALUES  (9999999, 9999999)

SELECT  DUMP(col1), DUMP(col2)
FROM    t_pk

DUMP(col1)                        DUMP(col2)
---                               ---
Typ=2 Len=5: 196,10,100,100,100   Typ=2 Len=5: 196,10,100,100,100

In Oracle, the NUMBERs are stored as centesimal digits of the numeric value normalized to 0.01 <= N < 1 and prepended with the exponent.

In the example above:

• 196 is the 192-based exponent (4).
• 10 is decimal 9
• 100‘s are decimal 99‘s

The whole number reads in decimal as 00.09 99 99 99 * (100 ^ 4) = 9,999,999

The more digits are required to satisfy the precision requested, the more of them will be stored of course.

When you insert a precise value into a less precise column, it just gets rounded to column’s precision and is stored rounded.

Therefore, it is safe performance-wise to declare you column NUMBER(38), since it implies no overhead over NUMBER(7, 0) (for the numbers that fit both types).

However, if your PRIMARY KEYs are integer by nature, you better specify precision as 0 to make sure no fractional value ever gets to your table.

Update:

@Mac also pointed that the clients may rely on the column datatype to figure out the values domain.

If your application expects an INT32, you should make your number a NUMBER(9) or below (or whatever type your client considers to be convertable to Int32).