Firebird 3.0

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CREATE TABLE TBKURSZEILEN(
  ID_KURSZEILE INTEGER GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY,
  DATUM DATE,
  FK_KONTRAKT INT,
  C VARCHAR(10)
);
EXECUTE BLOCK AS BEGIN
INSERT INTO TBKURSZEILEN(DATUM, FK_KONTRAKT, C) VALUES('2024-01-01', 5, 'A1');
INSERT INTO TBKURSZEILEN(DATUM, FK_KONTRAKT, C) VALUES('2024-02-01', 5, 'A2');
INSERT INTO TBKURSZEILEN(DATUM, FK_KONTRAKT, C) VALUES('2024-03-01', 5, 'A3');
INSERT INTO TBKURSZEILEN(DATUM, FK_KONTRAKT, C) VALUES('2024-04-01', 5, 'A4');
INSERT INTO TBKURSZEILEN(DATUM, FK_KONTRAKT, C) VALUES('2024-05-01', 5, 'A5');
INSERT INTO TBKURSZEILEN(DATUM, FK_KONTRAKT, C) VALUES('2024-06-01', 5, 'A6');
INSERT INTO TBKURSZEILEN(DATUM, FK_KONTRAKT, C) VALUES('2024-07-01', 5, 'A7');
INSERT INTO TBKURSZEILEN(DATUM, FK_KONTRAKT, C) VALUES('2024-08-01', 5, 'A8');
INSERT INTO TBKURSZEILEN(DATUM, FK_KONTRAKT, C) VALUES('2024-05-15', 5, 'A9');
INSERT INTO TBKURSZEILEN(DATUM, FK_KONTRAKT, C) VALUES('2024-06-15', 5, 'A0');
INSERT INTO TBKURSZEILEN(DATUM, FK_KONTRAKT, C) VALUES('2024-05-01', 6, 'B1');
INSERT INTO TBKURSZEILEN(DATUM, FK_KONTRAKT, C) VALUES('2024-06-01', 6, 'B2');
INSERT INTO TBKURSZEILEN(DATUM, FK_KONTRAKT, C) VALUES('2024-07-01', 6, 'B3');
INSERT INTO TBKURSZEILEN(DATUM, FK_KONTRAKT, C) VALUES('2024-08-01', 6, 'B4');
INSERT INTO TBKURSZEILEN(DATUM, FK_KONTRAKT, C) VALUES('2024-09-01', 6, 'B5');
INSERT INTO TBKURSZEILEN(DATUM, FK_KONTRAKT, C) VALUES('2024-10-01', 6, 'B6');
INSERT INTO TBKURSZEILEN(DATUM, FK_KONTRAKT, C) VALUES('2024-11-01', 6, 'B7');
INSERT INTO TBKURSZEILEN(DATUM, FK_KONTRAKT, C) VALUES('2024-12-01', 6, 'B8');
INSERT INTO TBKURSZEILEN(DATUM, FK_KONTRAKT, C) VALUES('2024-01-15', 7, 'C9');
INSERT INTO TBKURSZEILEN(DATUM, FK_KONTRAKT, C) VALUES('2024-02-15', 7, 'C0');
INSERT INTO TBKURSZEILEN(DATUM, FK_KONTRAKT, C) VALUES('2024-03-01', 7, 'C1');
INSERT INTO TBKURSZEILEN(DATUM, FK_KONTRAKT, C) VALUES('2024-04-01', 7, 'C2');
INSERT INTO TBKURSZEILEN(DATUM, FK_KONTRAKT, C) VALUES('2024-05-01', 7, 'C3');
INSERT INTO TBKURSZEILEN(DATUM, FK_KONTRAKT, C) VALUES('2024-06-01', 7, 'C4');
INSERT INTO TBKURSZEILEN(DATUM, FK_KONTRAKT, C) VALUES('2024-07-01', 7, 'C5');
INSERT INTO TBKURSZEILEN(DATUM, FK_KONTRAKT, C) VALUES('2024-08-01', 7, 'C6');
INSERT INTO TBKURSZEILEN(DATUM, FK_KONTRAKT, C) VALUES('2024-09-01', 7, 'C7');
END
27 rows affected

SELECT ID_KURSZEILE, DATUM, FK_KONTRAKT, C,
   (
   SELECT COUNT(*)
   FROM TBKURSZEILEN B
   WHERE B.DATUM=A.DATUM AND (B.FK_KONTRAKT = '5' OR  B.FK_KONTRAKT = '6')
   ) AS X
FROM TBKURSZEILEN A
WHERE (
  SELECT COUNT(*)
  FROM TBKURSZEILEN B
  WHERE B.DATUM=A.DATUM AND (B.FK_KONTRAKT = '5' OR  B.FK_KONTRAKT = '6')
  )=2 
  AND (A.FK_KONTRAKT = '5' OR  A.FK_KONTRAKT = '6')
ORDER BY DATUM, ID_KURSZEILE


ID_KURSZEILE
DATUM
FK_KONTRAKT
C
X


5
2024-05-01
5
A5
2

11
2024-05-01
6
B1
2

6
2024-06-01
5
A6
2

12
2024-06-01
6
B2
2

7
2024-07-01
5
A7
2

13
2024-07-01
6
B3
2

8
2024-08-01
5
A8
2

14
2024-08-01
6
B4
2
ID_KURSZEILE	DATUM	FK_KONTRAKT	C	X
5	2024-05-01	5	A5	2
11	2024-05-01	6	B1	2
6	2024-06-01	5	A6	2
12	2024-06-01	6	B2	2
7	2024-07-01	5	A7	2
13	2024-07-01	6	B3	2
8	2024-08-01	5	A8	2
14	2024-08-01	6	B4	2