What data type is recommended for ID columns?

Question

I realize this question is very likely to have been asked before, but I\'ve searched around a little among questions on StackOverflow, and I didn\'t really find an answer to

Answer 1

Any integer type of sufficient size to store anticipated data ranges. Generally 32 bit ints are viewed as too small (rightly or wrongly) for tables with a lot of rows or changes. A 64 bit int is plenty. Many databases won't have or won't use that integer type but will use a NUMBER type with specified scale and precision. 10-15 digits is a fairly common size.

The reason for choosing integer types is twofold:

1. Size; and
2. Speed.

The size of an integer is:

• 32 bit: 4 bytes;
• 64 bit: 8 bytes;
• Binary coded decimal: two digits per byte plus as much as a byte for sign, scale and/or precision.

Compare that to a GUID, which is 128 bits or a normal string, which is at least one byte per character (more in certain character encodings) plus an overhead that might be as little as one byte (terminating null) or could be much more in some cases.

Sorting integers is trivial and, assuming they are unique and the range is sufficiently small, can actually be done in O(n) time, compared to, at best, O(n log n).

also, just as importantly, most databases can generate unique IDs by means of auto-increment columns and/or sequences. Guaranteeing uniqueness in an application is otherwise actually quite hard and tends to result in bloated keys.

Plus auto-generated integer keys are typically either loosely or absolutely ordered (depending on database and configuration), which is a useful quality. Randomly generated GUIDs are basically unordered, which is far less useful.