CREATE TRIGGER TRANSACTION_START
ACTIVE ON TRANSACTION START
AS
BEGIN
  IF (RDB$GET_CONTEXT ('SYSTEM', 'READ_ONLY') = 'FALSE') THEN
    IN AUTONOMOUS TRANSACTION DO
      INSERT INTO USER_TRANSACTION (USER_NAME, TRANSACTION_ID) VALUES (CURRENT_USER, CURRENT_TRANSACTION);
END;

EXECUTE STATEMENT ...
WITH AUTONOMOUS TRANSACTION
AS USER "специальный" PASSWORD '12345'
ON EXTERNAL DATA SOURCE ...

RECREATE TABLE U_TRANS
EXTERNAL FILE '. . .'
(
    USER_NAME       CHAR(31),
    TRANSACTION_ID  CHAR(20),
    CONNECTION_ID   CHAR(20),
    CLIENT_PROCESS  CHAR(255),
    CLIENT_ADDRESS  CHAR(255),
    DATE_START      CHAR(26) DEFAULT CURRENT_TIMESTAMP NOT NULL
);

GRANT SELECT ON TABLE U_TRANS TO PUBLIC;

CREATE OR ALTER TRIGGER ON_TRANSACTION_START
ACTIVE ON TRANSACTION START
AS
BEGIN
  IF (RDB$GET_CONTEXT ('SYSTEM', 'READ_ONLY') = 'FALSE') THEN
    INSERT INTO U_TRANS (USER_NAME, TRANSACTION_ID, CONNECTION_ID, CLIENT_PROCESS, CLIENT_ADDRESS)
      VALUES (CURRENT_USER, CURRENT_TRANSACTION, CURRENT_CONNECTION, RDB$GET_CONTEXT('SYSTEM', 'CLIENT_PROCESS'), RDB$GET_CONTEXT('SYSTEM', 'CLIENT_ADDRESS'));
END;

GRANT SELECT, INSERT ON TABLE U_TRANS TO TRIGGER ON_TRANSACTION_START;