–asc 按升序排列
select t.amount,ROWNUM from T_STUDENT T order by T.times asc–desc 按降序排列
select t.amount,ROWNUM from T_STUDENT T order by T.times desc–类似
select * from T_STUDENT where username like '三%'–选择多个条件的数据
select * from T_STUDENT where username in('张三','张三9')–选择多个条件的数据
select * from T_STUDENT where username in(SELECT username FROM T_STUDENT )–是空判断
select * from T_STUDENT where age is null–非空判断
select * from T_STUDENT where age is not null–select的查询语句可支持多层
select * from T_STUDENT where (SELECT age FROM T_STUDENT WHERE AGE=78)=AGE–复制表的结构及数据
create table T_STUDENT as select * from T_STUDENT2–distinst rows 两个表的数据记录全部合并显示但是去除重select t.username, t.age from T_STUDENT t union select t.username, t.age from T_STUDENT t –all rows 两个表的数据记录全部合并显示
select t.username, t.age from T_STUDENT t union all select t.username, t.age from T_STUDENT t– left join inner join right join 左联结 内联结 右联结 – left join (左联接) 返回包括左表中的所有记录和右表中联结字段相等的记录 – right join (右联接) 返回包括右表中的所有记录和左表中联结字段相等的记录 – inner join (等值连接) 只返回两个表中联结字段相等的行
select t.name,d.pro_name,d.price from USERS t inner JOIN T_ORDER d on d.username_id = t.name select t.name,d.pro_name,d.price from USERS t,T_ORDER d where d.username_id(+) = t.name–分页
SELECT * FROM ( SELECT A.*, ROWNUM RN FROM (SELECT * FROM SIXGOD2) A WHERE ROWNUM <= 40 ) WHERE RN >= 1–分页第二个方式，可以使用between and的方式做分页
SELECT * FROM ( SELECT A.*, ROWNUM RN FROM (SELECT * FROM T_STUDENT) A ) WHERE RN BETWEEN 2 AND 4–条件取值decode,类似if else，后面可以写多个else
select DECODE(T.AGE,78,'张三78',26,'张三26',t.username), t.age from T_STUDENT t–条件取值case when，类似If else
select case T.AGE when 78 then '张三78' end from SIXGOD2 t–生成随机值
select sys_guid() from dual–判断是否为空，如果为空就显示第二个参数
select NVL (T.USERNAME_ID, ' IS NULL ') from T_ORDER t