Demonstrates how to use the select statement, next to emp, dept, salgrade table structure commentary.
Employee emp table Whether the data type field name is null Remarks -------- ----------- -------- -------- NUMBER the EMPNO ( 4 ) Number of employees VARCHAR2 ENAME ( 10 ) the name of the Y-employees VARCHAR2 JOB ( 9 ) the Y-Job NUMBER MGR ( . 4 ) the higher the number of the Y HIREDATE DATE Y entry date NUMBER SAL ( 7 , 2 ) the Y-month salary NUMBER COMM ( . 7 , 2 ) the Y bonus NUMBER the DEPTNO ( 2 ) the Y-department ------------------------------------------- job fields: Poor staff clerk salesman sales manager manager analyst Analyst president, president
department table dept Whether the data type field name is null Remarks -------- ----------- -------- -------- NUMBER the DEPTNO ( 2 ) department number VARCHAR2 DNAME ( 14 ) the Y-department name (LOC VARCHAR2 13 ) the Y-sector location ------------------------------------------- DNAME field: accounting Finance Department research R & D Business operations salgrade wage level table Whether the data type field name is null Remarks -------- --------- -------- -------- GRADE NUMBER Y level LOSAL NUMBER Y Minimum Wage HISAL NUMBER Y highest wages
1, see the table structure
desc emp;
2, all queries column
the SELECT * from the dept; - Note: Avoid quick to use select *, * use efficiency is relatively low, especially in large table to pay attention.
3, switch the display operation time, operation time displayed at the bottom.
set timing on/off;
eg: sql> insert into tb_stu values('0001','zhangsan',24);
1 row inserted executed in 0.015 seconds
4, insert into ... select ... statements copy table
语法：insert into table2(field1,field2,...) select value1,value2,... from table1
- Create tb_dept
create table tb_dept ( deptno number(4) not null, dname varchar2(14), loc varchar2(13) ) - Add primary key constraint ALTER Table tb_dept the Add constraint tb_dept Primary Key (DEPTNO);
--insert into...select...用法 insert into tb_dept (deptno, dname, loc) select a.deptno, a.dname, a.loc from dept a;
5, statistical select count (*) from emp;