往前走，一片诱人的新绿尽收眼底，那是满池的新荷。荷叶有的平展着圆盘浮在水面上；有的绿伞般在空中摇曳；有的兜着水珠把阳光反射得灿烂夺目；有的长得非常高，却未展开叶面，勇敢地挺立着。荷花则多半含苞待放，白中透粉的一朵朵花儿，活像一个个花仙子借着微风，在池中裙袂飞扬，翩然起舞。
Select * from tablename SQL> select * from employees;
Select select list from tablename
SQL> select employee_id,first_name from employees;
Select distinct … from tablename
SQL> select distinct manager_id from employees;
||连接符使用以及 加减乘除以及括号的使用
SQL> select employee_id,first_name||'.'||last_name,salary*(1+0.1)/100,manager_id
2 from employees;
+-做正负号使用
SQL> select -salary from employees;
<>,>,<,=,!=等比较操作符
SQL> select * from employees where salary >13000;
SQL> select * from employees where salary <13000;
SQL> select * from employees where salary <>13000;
SQL> select * from employees where salary =13000;
In
SQL> select -salary from employees where employee_id in (100,101,102);
SQL> select -salary from employees where employee_id in (select employee_id from employees);
not in
SQL> select -salary from employees where employee_id not in (100,101,102);
Any(比任意一个都)
select * from employees where employee_id >any(100,101,102);
some 是 SQL-92 标准的 any 的等效物
select * from employees where employee_id >any(100,101,102);
all（比所有的都）
select * from employees where employee_id >all(100,101,102);
between and
select * from employees where employee_id between 100 and 102;
not between and
select * from employees where employee_id not between 100 and 102;
逻辑操作符
And 和 or
select * from employees where employee_id > 100 and employee_id < 1000;
select * from employees where employee_id > 100 or employee_id < 1000;
Order by
Desc
select * from employees where employee_id between 100 and 102 order by employee_id desc;
Asc
select * from employees where employee_id between 100 and 102 order by employee_id asc;
dual哑元表没有表需要查询的时候可以用它
select sysdate from dual;
select 1*2*3*4*5 from dual;
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