mysql里的BIGINT类型有人用吗

INT is a four-byte signed integer. BIGINT is an eight-byte signed integer.

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. 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).