website is vulnerable

sql injection error is : Query failed: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '\'a' at line 1

i use command order by and i got 23 columns but when i paste link in browser like this

UNION ALL SELECT 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20 ,21,22,23--

page load normally and i can not see printable field

can help me what i am doing mistake