Code:
 say2
(n)  title

(1)   Mom
(2)   WTD
(3)   SUN
(4)   Earth
(5)   Asia
(6)   Europe
(7)   Venus
(8)   Korea
Let's suppose I have my table named "say2" like the above.

The code1 below produces the result1 below.
Code:
code1
SELECT n, title
FROM say2
WHERE n=1 or n =3 or n =5

result1
(1) Mom
(3) SUN
(5) Asia
And the code2 below produces the result2 below.
Code:
code2
SELECT n, title
FROM say2
WHERE n=5 or n =7 or n =8

result2
(5) Asia
(7) Venus
(8) Korea
Let's UNION them like the below code3 and its result3.
Code:
code3
SELECT n, title
FROM say2
WHERE n=1 or n =3 or n =5
UNION
SELECT n, title
FROM say2
WHERE n=5 or n =7 or n =8

result3
(1) Mom
(3) SUN
(5) Asia
(7) Venus
(8) Korea
Now I think It would be better if there is the opposite of UNION in mySQL.
UNION means result1 + result2.
I mean that the opposite of UNION means result1 - result2.

The following would-be code4 doesn't work correctly, but I hope it shows what I want.
Code:
would-be code4
SELECT n, title
FROM say2
WHERE n=1 or n =3 or n =5
the opposite of UNION 
SELECT n, title
FROM say2
WHERE n=5 

target result4
(1) Mom
(3) SUN

or 

would-be code5
SELECT n, title
FROM say2
WHERE n=1 or n =3 or n =5
the opposite of UNION 
SELECT n, title
FROM say2
WHERE n=5 or n =7 or n =8

target result5
(1) Mom
(3) SUN