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;
下一篇: oracle的序列号(sequence)
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