首页 > 数据库 > Oracle >

Oracle中常用SQL语句(一)

2017-07-03

Oracle中常用SQL语句(一)。

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1

select * 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2

select * 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;

相关文章
最新文章
热点推荐