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;