Oracle中常用SQL语句（一）

1、常用SQL

--新建表：create table table1( id varchar(300) primary key, name varchar(200) not null);--插入数据   insert into table1 (id,name) values ('aa','bb');--更新数据   update table1 set id = 'bb' where id='cc';--删除数据   delete from table1 where id ='cc';--删除表    drop table table1;--修改表名： alter table table1 rename to table2;--表数据复制：insert into table1 (select * from table2);--复制表结构： create table table1 select * from table2 where 1>1;--复制表结构和数据：create table table1 select * from table2;--复制指定字段： create table table1 as select id, name from table2 where 1>1;--条件查询： select id,name (case gender when 0 then '男' when 1 then ‘女’ end  ) gender from  table1;

2、数学函数

--绝对值：abs()select abs(-2) value from dual;          --(2)--取整函数（大）：ceil（）select ceil(-2.001) value from dual;       --(-2)--取整函数（小）：floor（）select floor(-2.001) value from dual;       --(-3)--取整函数（截取）：trunc（）select trunc(-2.001) value from dual;       -- (-2)--四舍五入：round（）select round(1.234564,4) value from dual;       --(1.2346)--取平方：Power（m,n）select power(4,2) value from dual;       --(16)--取平方根:SQRT()select sqrt(16) value from dual;       --(4)--取随机数:dbms_random(minvalue,maxvalue)select dbms_random.value() from dual;  (默认是0到1之间)select dbms_random.value(2,4) value from dual;  （2-4之间随机数）--取符号：Sign()select sign(-3) value from dual; --(-1)select sign(3) value from dual; --(1)--取集合的最大值:greatest(value)select greatest(-1,3,5,7,9) value from dual;       --(9)--取集合的最小值:least(value)select least(-1,3,5,7,9) value from dual;       --(-1)--处理Null值：nvl(空值，代替值)select  nvl(null,10) value from dual;     --(10)select nvl(score,10) score from student;  --如果sccore为空，则为10，否则为score

3、rownum相关

--rownum小于某个数时可以直接作为查询条件（注意oracle不支持select top）select * from student where rownum <3;--查询rownum大于某个数值,需要使用子查询，并且rownum需要有别名select * from (select rownum rn ,id,name from student) where rn>2;select * from (select rownum rn, student.* from student) where rn >3;--区间查询select * from (select rownum rn, student.* from student) where rn >3 and rn<6;--排序+前n条select * from (select rownum rn, t.* from ( select d.* from DJDRUVER d order  by drivernumber)t )p where p.rn<10;--排序+区间查询1select * from (select rownum rn, t.* from ( select d.* from DJDRIVER d order by DJDRIVER_DRIVERTIMES)t )p where p.rn<9 and p.rn>6;--排序+区间查询2select * from (select rownum rn, t.* from ( select d.* from DJDRIVER d order by DJDRIVER_DRIVERTIMES)t where rownum<9 )p where p.rn>6;  --效率远高于方式1

4、分页查询（假设每页显示10条）

4.1 不包含排序

--效率低select * from (select rownum rn, d.* from DJDRIVER d  )p where p.rn<=20 and p.rn>=10;select * from (select rownum rn, d.* from DJDRIVER d  )p where p.rn between 10 and 20;--效率高 select * from (select rownum rn, d.* from DJDRIVER d where rownum<=20 )p where p.rn>=10;

4.2 包含排序

--排序+区间查询1（效率低）select * from (select rownum rn, t.* from ( select d.* from DJDRIVER d order by DJDRIVER_DRIVERTIMES)t )p where p.rn<=20 and p.rn>=10;select * from (select rownum rn, t.* from ( select d.* from DJDRIVER d order by DJDRIVER_DRIVERTIMES)t )p where p.rn between 10 and 20;--排序+区间查询2（效率高） select * from (select rownum rn, t.* from ( select d.* from DJDRIVER d order by DJDRIVER_DRIVERTIMES)t where rownum<=20 )p where p.rn>=10;