Submitted by: @hvlad

1. Prepare metatada:

CREATE TABLE TABLE1 (
FIELD1 INTEGER NOT NULL
);
ALTER TABLE TABLE1 ADD CONSTRAINT PK_TABLE1 PRIMARY KEY (FIELD1);

CREATE TABLE TABLE2 (
FIELD1 INTEGER NOT NULL,
DATE1 DATE NOT NULL
);
ALTER TABLE TABLE2 ADD CONSTRAINT PK_TABLE2 PRIMARY KEY (FIELD1, DATE1)
USING DESCENDING INDEX PK_TABLE2;
CREATE INDEX IDX_TABLE2 ON TABLE2 (FIELD1, DATE1);
COMMIT;

2. Problem query:
WITH AA
AS (SELECT T1.FIELD1,
(SELECT FIRST 1 T2.DATE1
FROM TABLE2 T2
WHERE T2.FIELD1 = T1.FIELD1
PLAN(T2 INDEX(IDX_TABLE2))
ORDER BY T2.FIELD1 ASC, T2.DATE1 ASC) AS DATE1
FROM TABLE1 T1)

SELECT DATE1, COUNT('x')
FROM AA
GROUP BY 1

Note, if PLAN clause commented out, Firebird will not crash

Commits: 5e296cb FirebirdSQL/fbt-repository@7c68250