> select contract_id, contract_ext_id
  from contract.contract
 where contract_id = 62948;

 contract_id | contract_ext_id
-------------+-----------------
       62948 |           60737
       62948 |
(2 строки)

> select contract_id, contract_ext_id
  from contract.contract
 where contract_id = 62948
   and contract_ext_id <> 60737;

 contract_id | contract_ext_id
-------------+-----------------
(0 строк)

> select contract_id, contract_ext_id
  from contract.contract
 where contract_id = 62948
   and coalesce(contract_ext_id,0) <> 60737;

 contract_id | contract_ext_id
-------------+-----------------
       62948 |
(1 строка)

> select version();
                                                  version
-----------------------------------------------------------------------------------------------------------
 PostgreSQL 9.5.10 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-18), 64-bit
(1 строка)

----------------

contract_id INTEGER,
contract_ext_id INTEGER,