Select operators or set operators

Also called a set operators

Union:
This is combines the results of two queries and returns the set of distinct rows returned by either query.
Union All:
This is combines the results of two queries and returns all rows returned by either query,including  duplicates.
Intersect:

This combines the results of two queries and returns the set of distinct rows returned by both queries

Minus:

This combines the results of two queries and returns the distinct rows that were in the first query, but not in the second

 
Other select operators

(+)Denotes that the preceding column is an outer join

* wildcard operator.Equals all columns in a select statement 

Prior Denotes a parent-child relation ship operator in prior

Sample Emp Tables Backup

CREATE TABLE DEPT ( DEPTNO  NUMBER(2) NOT NULL primary key,
                    DNAME   CHAR(14),
                    LOC     CHAR(13));

INSERT INTO DEPT VALUES (10,'ACCOUNTING','NEW YORK');
INSERT INTO DEPT VALUES (20,'RESEARCH','DALLAS');
INSERT INTO DEPT VALUES (30,'SALES','CHICAGO');
INSERT INTO DEPT VALUES (40,'OPERATIONS','BOSTON');

CREATE TABLE EMP (
 EMPNO               NUMBER(4) NOT NULL,
 ENAME               CHAR(10),
 JOB                 CHAR(9),
 MGR                 NUMBER(4) CONSTRAINT EMP_SELF_KEY REFERENCES EMP (EMPNO),
 HIREDATE            DATE,
 SAL                 NUMBER(7,2),
 COMM                NUMBER(7,2),
 DEPTNO              NUMBER(2) NOT NULL,
 CONSTRAINT EMP_FOREIGN_KEY FOREIGN KEY (DEPTNO) REFERENCES DEPT (DEPTNO),
 CONSTRAINT EMP_PRIMARY_KEY PRIMARY KEY (EMPNO));

INSERT INTO EMP VALUES (7839,'KING','PRESIDENT',NULL,'17-NOV-81',5000,NULL,10);
INSERT INTO EMP VALUES (7698,'BLAKE','MANAGER',7839,'1-MAY-81',2850,NULL,30);
INSERT INTO EMP VALUES (7782,'CLARK','MANAGER',7839,'9-JUN-81',2450,NULL,10);
INSERT INTO EMP VALUES (7566,'JONES','MANAGER',7839,'2-APR-81',2975,NULL,20);
INSERT INTO EMP VALUES (7654,'MARTIN','SALESMAN',7698,'28-SEP-81',1250,1400,30);
INSERT INTO EMP VALUES (7499,'ALLEN','SALESMAN',7698,'20-FEB-81',1600,300,30);
INSERT INTO EMP VALUES (7844,'TURNER','SALESMAN',7698,'8-SEP-81',1500,0,30);
INSERT INTO EMP VALUES (7900,'JAMES','CLERK',7698,'3-DEC-81',950,NULL,30);
INSERT INTO EMP VALUES (7521,'WARD','SALESMAN',7698,'22-FEB-81',1250,500,30);
INSERT INTO EMP VALUES (7902,'FORD','ANALYST',7566,'3-DEC-81',3000,NULL,20);
INSERT INTO EMP VALUES (7369,'SMITH','CLERK',7902,'17-DEC-80',800,NULL,20);
INSERT INTO EMP VALUES (7788,'SCOTT','ANALYST',7566,'09-DEC-82',3000,NULL,20);
INSERT INTO EMP VALUES (7876,'ADAMS','CLERK',7788,'12-JAN-83',1100,NULL,20);
INSERT INTO EMP VALUES (7934,'MILLER','CLERK',7782,'23-JAN-82',1300,NULL,10);

CREATE TABLE BONUS (
ENAME               CHAR(10),
JOB                 CHAR(9),
SAL                 NUMBER,
COMM                NUMBER);

CREATE TABLE SALGRADE
 ( GRADE               NUMBER,
   LOSAL               NUMBER,
   HISAL               NUMBER);

INSERT INTO SALGRADE VALUES (1,700,1200);
INSERT INTO SALGRADE VALUES (2,1201,1400);
INSERT INTO SALGRADE VALUES (3,1401,2000);
INSERT INTO SALGRADE VALUES (4,2001,3000);
INSERT INTO SALGRADE VALUES (5,3001,9999);

Q: How to enter a single quotation mark in Oracle?

Ans: Although this may be a undervalued question, I got many a search for my blog with this question. This is where I wanted to address this question elaborately or rather in multiple ways.

Method 1
The most simple and most used way is to use a single quotation mark with two single quotation marks in both sides.

SELECT 'test single quote''' from dual;

The output of the above statement would be:
test single quote'

Simply stating you require an additional single quote character to print a single quote character. That is if you put two single quote characters Oracle will print one. The first one acts like an escape character.

This is the simplest way to print single quotation marks in Oracle. But it will get complex when you have to print a set of quotation marks instead of just one. In this situation the following method works fine. But it requires some more typing labour.

Method 2
I like this method personally because it is easy to read and less complex to understand. I append a single quote character either from a variable or use the CHR() function to insert the single quote character.

The same example inside PL/SQL I will use like following:

DECLARE
l_single_quote CHAR(1) := '''';
l_output VARCHAR2(20);
BEGIN
SELECT 'test single quote'||l_single_quote
INTO l_output FROM dual;
DBMS_OUTPUT.PUT_LINE(l_single_quote);
END;

The output above is same as the Method 1.

Now my favourite while in SQL is CHR(39) function. This is what I would have used personally:

SELECT 'test single quote'||CHR(39) FROM dual;

The output is same in all the cases.