Oracle,SQLserver,mySQL,postgreSQL,DB2区别
1.端口
Oracle----1521
SqlServer---1433
MySQL-----3306
postgreSQL-----5432
DB2-----50000
2.自动生成主键
Oracle----sequence---select seq.nextval from dual;select seq.currval from dual;
SqlServer---identity(1,1)--studentId int primary key identity(1,1),
MySQL-----auto_increment ----studentId int primary key auto_increment,
postgreSQL-----sequence--------select currval('seq');select nextval('seq')
3.分页查询11-15
Oracle----select * from (select rownum rm,e.* from emp e) where rownum<=5 and rm>=11;
SqlServer---select top 5 * from student where sno not in (select top 10 sno from student);
MySQL---select * from student limit 10,5;(limit 5 offset 10)
postgreSQL---select * from student limit 5 offset 10;
DB2----select * from (select a.* ,rownumber() over() as rowid from emp a) as p where
p.rowid > 10 AND p.rowid < 16;
4.默认最大连接数
MySql---100
Oracle---150
PostgreSql---100
5.常用sql
mysql--select * from student limit 10 --查询前十条
oracle-- select * from student where rownum<=10 --查询前十条
select * from student where rownum=1 --这样可以,rownum=2不支持