Oracle Getting Started sixth day (middle)--set operator (orthogonal difference set)

I. Overview

　　What is the 1.SET operator?　

To concatenate multiple queries into a new query with the SET operator

　　　　　　Union/union all--and set

　　　　　　intersect--intersection

　　　　　　minus--difference Set (a\b=a the elements in B are removed)

　　　　For MySQL, the intersection, the difference set, reference : http://blog.csdn.net/goodleiwei/article/details/42149567

　　2. Illustrations

　　　

second, intersection--union

Union intersection (automatic de-weight and requires two result set columns to be merged)

SELECT *  from employees1 UNION SELECT *  from Employees2

　　　UNION all does not go heavy:

SELECT *  from employees1 UNION  All SELECT *  from Employees2

　　　　The sorting can be done in the following ways: (Because the department_id is the 11th column, so directly write the above number can)

SELECT *  from employees1 UNION SELECT *  from Employees2 ORDER  by  One

　　　　You can also take a second layer of the wording, reference:https://www.2cto.com/database/201210/163404.html

　　Of course, if the columns do not match, you can adjust them in the following form:

SELECT department_id, to_number (null) location        , hire_datefrom    EmployeesUNIONSELECT department_id, location_id,  to_date (null)  from   Departments;

SELECT employee_id, Job_id,salary  from    EmployeesUNIONSELECT employee_id, job_id,0from   job_ History

third, intersection--intersect

　　

SELECT *  from employees1 INTERSECT SELECT *  from Employees2

Four, the difference set--minus

　　

SELECT employee_id,job_id  from    employeesminusSELECT  employee_id,job_idfrom   job_history;

Oracle Getting Started sixth day (middle)--set operator (orthogonal difference set)