数据库约束长度前两位

alter table CS01 add constraint CK_A800 check (LEN(A8)=8)

alter table CS01 add constraint CK_A8001 check (A8 like '00%')

alter table CS01 add constraint CK_A8003 check (ascii(substring(A8,3,1))>=48 and ascii(substring(A8,3,1))<=57)

alter table CS01 add constraint CK_A8004 check (ascii(substring(A8,4,1))>=48 and ascii(substring(A8,4,1))<=57)

--下划线是通配符

alter table CS01 add constraint CK_A8005 check (ascii(substring(A8,5,1))>=ascii('_'))

--只允许输入大写字母

alter table CS01 add constraint CK_A8006 check (ascii(substring(A8,6,1))>=65 and ascii(substring(A8,6,1))<=90)

alter table CS01 add constraint CK_A8007 check (ascii(substring(A8,7,1))>=65 and ascii(substring(A8,7,1))<=90)

alter table CS01 add constraint CK_A8008 check (ascii(substring(A8,8,1))>=65 and ascii(substring(A8,8,1))<=90)我也是菜鸟一个 这么写看着确实有点傻

你是什么数据库，如果是oracle，那么你可以用这个语句

select 工号 from tablename where substr(工号，1,2)=‘10’

substr函数的意思，第一个参数，要截取的字符串，第二个参数的意思是从第几位起，第三个参数是取几位。

用order 倒叙字段

select * from user where 1=1 order by age desc

这个是在用户表中，用年龄倒序的

去3行数据 mysql的 select * from user where 1=1 order by age desc limit 3

去3行数据 oracle的 select * from user where 1=1 order by age desc rownum 3

---