since NUMBER(8) is not enough to store the maximum number of bigint.
Oracle NUMBER(p,0) as handled as integer
because there is no dedicated integer sql data type exist in Oracle database.

Also NUMBER(p,s) precision can take up to 38. p means the number of digits, not the byte length.
bigint type needs 19 digits as follows.

	$ irb
	2.2.2 :001 > limit = 8
	 => 8
	2.2.2 :002 > maxvalue_of_bigint = 1 << ( limit * 8 - 1)
	 => 9223372036854775808
	2.2.2 :003 > puts maxvalue_of_bigint.to_s.length
	19
	 => nil
	2.2.2 :004 >