Union and Union All Concept in SQL

Difference between Union and Union All 

select * from XX_STUDENT_TL

STUDENT_NAME	MARKS	PHYSICAL_MARKS	RESULT	GRADE
Amit	33	80	F	A
Bharat	20	30	F
Jai Prakash	99	100	P	A++
Manoj	20	98	F	A+
Pinky	90	30	P	A+
Rahul	45	55
Ravi	50	90	P	A+
Sanjay	80	40	P	A+

--====================================================

UNION

--====================================================

select * from XX_STUDENT_TL

where RESULT = 'P'

UNION

select * from XX_STUDENT_TL

WHERE GRADE = 'A+'

STUDENT_NAME	MARKS	PHYSICAL_MARKS	RESULT	GRADE
Jai Prakash	99	100	P	A++
Manoj	20	98	F	A+
Pinky	90	30	P	A+
Ravi	50	90	P	A+
Sanjay	80	40	P	A+

--====================================================

UNION ALL

--====================================================

select * from XX_STUDENT_TL

where RESULT = 'P'

UNION ALL

select * from XX_STUDENT_TL

WHERE GRADE = 'A+'

order by 1

STUDENT_NAME	MARKS	PHYSICAL_MARKS	RESULT	GRADE
Jai Prakash	99	100	P	A++
Manoj	20	98	F	A+
Pinky	90	30	P	A+
Pinky	90	30	P	A+
Ravi	50	90	P	A+
Ravi	50	90	P	A+
Sanjay	80	40	P	A+
Sanjay	80	40	P	A+

--====================================================

Mandatory Rules for Union and Union ALL

--====================================================

select STUDENT_NAME,RESULT, MARKS,GRADE  from XX_STUDENT_TL

where RESULT = 'P'

UNION

select GRADE ,GRADE,MARKS,RESULT   from XX_STUDENT_TL

WHERE GRADE = 'A+'

STUDENT_NAME	RESULT	MARKS	GRADE
A+	A+	20	F
A+	A+	50	P
A+	A+	80	P
A+	A+	90	P
Jai Prakash	P	99	A++
Pinky	P	90	A+
Ravi	P	50	A+
Sanjay	P	80	A+

select STUDENT_NAME,RESULT, MARKS,GRADE  from XX_STUDENT_TL

where RESULT = 'P'

UNION

select  STUDENT_NAME,RESULT, MARKS,GRADE from XX_STUDENT_TL

WHERE GRADE = 'A+'

STUDENT_NAME	RESULT	MARKS	GRADE
Jai Prakash	P	99	A++
Manoj	F	20	A+
Pinky	P	90	A+
Ravi	P	50	A+
Sanjay	P	80	A+