Select all values ​​except repetitive

I have three tables. First. Name: ExTable. Column: id(integer), name(text)

--------------------
|  id  |    name |
--------------------
|  1   |    exA    |
|  2   |    exB    |
|  3   |    exC    |
--------------------

Second: Name: CerTable. Column: id(integer), name(text)

-------------------
|  id  |    name  |
-------------------
|  1   |    first |
|  2   |    second|
|  3   |    third |
-------------------

Third: Name: CerExTable. Column: id(integer), id_cer(integer) from CerTable, id_ex(integer) - from ExTable.

----------------------------------
|  id  |      id_cer     | id_ex |
----------------------------------
|  1   |    1 (first)    |1 (exA)|
|  2   |    1 (first)    |2 (exB)|
|  3   |    1 (first)    |3 (exC)|
|  3   |    2 (second)   |1 (exA)|
|  3   |    2 (second)   |3 (exC)|
|  3   |    3 (third)    |2 (exB)|
---------------------------------

So, I want to select data with id_cer = 2 and id_ex !=(not equal!) 1 and 3. So, I want to get next value: exB. if id_cer=3, I want to get: exA, exC, If id_cer=1, I want to get null.

My SQL query:

SELECT ExTable.id, ExTable.name FROM ExTable, CerExTable WHERE CerExTable.id_cer = 2 AND CerExTable.id_ex != ExTable.id

Expected result:

--------------------
|  id  |    name   |
--------------------
|  2   |    exB    |
--------------------

But result is next:

--------------------
|  id  |    name   |
--------------------
|  2   |    exB    |
|  3   |    exC    |
|  1   |    exA    |
|  2   |    exB    |
--------------------

because this query get data firstly for "except exA" - exB, exC, and then "except C" - exA, exB

How to get data exception instead of two lines(for example) "at one time"?