I'm using Firebird 1.5 Final Release (Win32).

The DDL is as follows:

CREATE TABLE L_WORKSELENA (
NUM_REC SMALLINT,
KOD CHAR(8),
KLASS_STR VARCHAR(50),
ED_IZM VARCHAR(10),
ARTICUL VARCHAR(20),
KOL NUMERIC(15,5),
CENA NUMERIC(15,5),
SUMMA NUMERIC(10,2)
);

CREATE INDEX IX_L_WORKSELENA_NUM_REC ON L_WORKSELENA (NUM_REC);

The components used are IB Xpress 6.08.