1.去掉重复的数值
select owner from pet; select distinct owner from pet;
2.
CREATE TABLE t1 (year YEAR(4), month INT(2) UNSIGNED ZEROFILL, day INT(2) UNSIGNED ZEROFILL); INSERT INTO t1 VALUES(2000,1,1),(2000,1,20),(2000,1,30),(2000,2,2), (2000,2,23),(2000,2,23);
year(4)
insert into time values(78); #数据库中显示：1978
insert into time values(‘78‘); #数据库中显示：1978
insert into time values(‘1978‘); #数据库中显示：1978
UNSIGNED:
将数字类型无符号化，这与C和C++这些程序语言的unsigned含义相同。
INT的类型范围-2 147 483 648~2 147 483 647
INT UNSIGNED范围0~4 294 967 295
原文：http://www.cnblogs.com/mavischen916/p/7294280.html