Types in MySQL: BigInt(20) vs Int(20)

Question

I was wondering what the difference between BigInt, MediumInt, and Int are... it would seem obvious that they would allow for larger numbers; however, I can make an Int(20) or a BigInt(20) and that would make seem that it is not necessarily about size.

Some insight would be awesome, just kind of curious. I have been using MySQL for a while and trying to apply business needs when choosing types, but I never understood this aspect.

Answer 1

See http://dev.mysql.com/doc/refman/8.0/en/numeric-types.html

• INT is a four-byte signed integer.

• BIGINT is an eight-byte signed integer.

They each accept no more and no fewer values than can be stored in their respective number of bytes. That means 2³² values in an INT and 2⁶⁴ values in a BIGINT.

The 20 in INT(20) and BIGINT(20) means almost nothing. It's a hint for display width. It has nothing to do with storage, nor the range of values that column will accept.

Practically, it affects only the ZEROFILL option:

CREATE TABLE foo ( bar INT(20) ZEROFILL );
INSERT INTO foo (bar) VALUES (1234);
SELECT bar from foo;

+----------------------+
| bar                  |
+----------------------+
| 00000000000000001234 |
+----------------------+

It's a common source of confusion for MySQL users to see INT(20) and assume it's a size limit, something analogous to CHAR(20). This is not the case.