Describe the bug
When using sqlmap against a firebird backend, the -C options does not work properly.

When counting the number of items in the column, the select request appends the database name FIREBIRD_MASTERDB to the column name, which does not exists in a firebird context.

The consequence is that sqlmap shows all rows as NULL.

To Reproduce

1. Run sqlmap with the options -C MY_COLUMN_NAME on an sql injection with a firebird backend
2. See all rows reported as NULL

Expected behavior
sqmap should have a positive count of rows and start enumerating all rows.

Running environment:

• sqlmap version: 1.5.2
• Installation method: pacman -S sqlmap
• Operating system: Archlinux
• Python version: 3.9.1

Target details:

• DBMS: Firebird

Additional context
This problem can be avoided by retrieving the data using a select query.

It is also possible to write a tamper script to clear the invalid database name in all requests:

from lib.core.enums import PRIORITY

__priority__ = PRIORITY.NORMAL

def tamper(payload, **kwargs):

    retVal = payload.replace("FIREBIRD_MASTERDB.","")
    return retVal