EXECUTE BLOCK
RETURNS (VAL INTEGER)
AS
DECLARE VARIABLE VAL_PARAM VARCHAR(30000);
DECLARE VARIABLE LEN INTEGER;
BEGIN
    RDB$SET_CONTEXT('USER_SESSION', LPAD('', 100, '0'), LPAD('', 100, '1'));
    VAL_PARAM = RDB$GET_CONTEXT('USER_SESSION', LPAD('', 100, '0'));
    VAL = CHAR_LENGTH(:VAL_PARAM);
    SUSPEND;
END

SELECT * FROM MON$CONTEXT_VARIABLES

Arithmetic overflow or division by zero has occurred.
arithmetic exception, numeric overflow, or string truncation.
string right truncation.
expected length 80, actual 100.

Таблица 7.3. Параметры функции RDB$GET_CONTEXT
Тип возвращаемого результата: VARCHAR(255)

CREATE TABLE MON$CONTEXT_VARIABLES (
    MON$ATTACHMENT_ID   BIGINT,
    MON$TRANSACTION_ID  BIGINT,
    MON$VARIABLE_NAME   VARCHAR(80) CHARACTER SET NONE,
    MON$VARIABLE_VALUE  VARCHAR(32765) CHARACTER SET NONE
);

EXECUTE BLOCK
RETURNS (VAL INTEGER)
AS
DECLARE VARIABLE PARAM VARCHAR(30000);
DECLARE VARIABLE VAL_PARAM VARCHAR(30000);
DECLARE VARIABLE LEN INTEGER;
BEGIN
    PARAM = LPAD('', 10000, '0');
    LEN = CHAR_LENGTH(:PARAM);
    RDB$SET_CONTEXT('USER_SESSION', 'CONT_PARAM', :PARAM);
    VAL_PARAM = RDB$GET_CONTEXT('USER_SESSION', 'CONT_PARAM');

    VAL = CHAR_LENGTH(:VAL_PARAM);
    SUSPEND;
END

SELECT * FROM MON$CONTEXT_VARIABLES

SELECT RDB$GET_CONTEXT('USER_SESSION', 'CONT_PARAM') FROM RDB$DATABASE

Arithmetic overflow or division by zero has occurred.
arithmetic exception, numeric overflow, or string truncation.
string right truncation.
expected length 255, actual 10000.