2010/8/18 João Luiz <jll.listas@...>

> I'm using Firebird 2.1.3.

So you certainly made a typo somewhere

$ isql localhost:employee -user SYSDBA -password masterkey
Database: localhost:employee, User: SYSDBA
SQL> show version;
ISQL Version: UI-V2.1.3.18185 Firebird 2.1
Server version:
Firebird/Darwin/Intel64 (access method), version "UI-V2.1.3.18185 Firebird 2.1"
Firebird/Darwin/Intel64 (remote server), version "UI-V2.1.3.18185
Firebird 2.1/tcp (callandor.local)/P11"
Firebird/Darwin/Intel64 (remote interface), version "UI-V2.1.3.18185
Firebird 2.1/tcp (callandor.local)/P11"
on disk structure version 11.1
SQL> SELECT EMP_NO, case EMP_NO when 11 then 'oi' end as caso
CON> FROM EMPLOYEE;

EMP_NO CASO
======= ======
2 <null>
4 <null>
5 <null>
8 <null>
9 <null>
11 oi
12 <null>
14 <null>