Hi,

I have 2 tables (relation: T100 and T110 ==> 1:n)

CREATE TABLE T100 (
T100_ID INTEGER NOT NULL,
T100_COL1 VARCHAR(40),
T100_COL2 SMALLINT,
CONSTRAINT PK_T100 PRIMARY KEY (T100_ID)
);

CREATE TABLE T110 (
T110_ID INTEGER NOT NULL,
T100_ID INTEGER NOT NULL,
T110_NR INTEGER NOT NULL,
CONSTRAINT PK_T110 PRIMARY KEY (T110_ID)
);

CREATE UNIQUE DESC INDEX IDX_T110 ON T110 (T100_ID,T110_NR);

ALTER TABLE T110
ADD CONSTRAINT FK_T110_REF_T100 FOREIGN KEY (T100_ID)
REFERENCES T100 (T100_ID);


Select:
SELECT T100.T100_COL1
, T100.T100_COL2
, T110.T110_NR
FROM T110
JOIN T100
ON T100.T100_ID = T110.T100_ID
ORDER BY T110.T100_ID DESC, T110.T110_NR DESC

1. If the tables are empty, than:
PLAN JOIN (T110 ORDER IDX_T110,T100 INDEX (PK_T100))

2. If it contains records, than:
PLAN SORT (JOIN (T100 NATURAL,T110 INDEX (FK_T110_REF_T100)))
^^^^^^^^^^^^^^ why?

Why does not the server (FB 1.5.2.4731) use the indexes
according to the first plan (in case of empty tables)?

Regards,
Norbert