What is the difference between precision and scale?
Precision is the number of significant digits. Oracle guarantees the portability of numbers with precision ranging from 1 to 38.
Scale is the number of digits to the right (positive) or left (negative) of the decimal point. The scale can range from -84 to 127.
In your case, ID with precision 6 means it won't accept a number with 7 or more significant digits.
Reference:
http://download.oracle.com/docs/cd/B28359_01/server.111/b28318/datatype.htm#CNCPT1832
That page also has some examples that will make you understand precision and scale.
Precision is the total number of digits, can be between 1 and 38.
Scale is the number of digits after the decimal point, may also be set as negative for rounding.
Example:
NUMBER(7,5): 12.12345
NUMBER(5,0): 12345
More details on the ORACLE website:
https://docs.oracle.com/cd/B28359_01/server.111/b28318/datatype.htm#CNCPT1832