Oracle Basic Query filtering sort instances

Basic query:

View plain-Query All employees ' information select * from EMP;   --Set the line wide set Linesize 120;   --Sets the width of the column width to four digits col empno for 9999;   --Set column width, A is a string of eight-bit length col ename for A8--set pagesize display 30 records per page set pagesize 30;   Arithmetic expressions are supported in--sql, note: If an expression contains a null value, the entire expression is an empty select Empno,ename,sal,sal*12,comm,sal*12+comm from EMP;   --Using an empty filter function, if comm is empty, replaces the Select EMPNO,ENAME,SAL,SAL*12,COMM,SAL*12+NVL (comm,0) from EMP with 0; --three ways to use aliases, aliases have the difference between the unique quotes: with double quotes can contain spaces and special characters, without double quotes cannot select Empno as "employee number", ename "name", Sal monthly salary, COMM,SAL*12+NVL (comm,0)   Annual income from EMP;   For Disctinct, the same record is taken only once select distinct deptno from EMP;   -When disctinct with multiple values, it is considered to be the same record select distinct deptno,job from emp when Deptno and job are the same; --Use of connectors