Firebird 3.0

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CREATE TABLE data1(
  field1 int,
  field2 varchar(20),
  field3 varchar(20),
  field4 decimal(18,2)
);
EXECUTE BLOCK AS BEGIN
INSERT INTO data1(field1, field2, field3, field4) VALUES(0,'aaaaaaa', 'ABC', 12.20);
INSERT INTO data1(field1, field2, field3, field4) VALUES(0,'aaaaaaa', 'DEF', 23.20);
INSERT INTO data1(field1, field2, field3, field4) VALUES(0,'aaaaaaa', 'GHI', 45.20);
INSERT INTO data1(field1, field2, field3, field4) VALUES(0,'aaaaaaa', 'JKL', 32.20);
INSERT INTO data1(field1, field2, field3, field4) VALUES(0,'aaaaaaa', 'MNO', 44.20);
INSERT INTO data1(field1, field2, field3, field4) VALUES(0,'aaaaaaa', 'PQR', 56.20);
INSERT INTO data1(field1, field2, field3, field4) VALUES(0,'aaaaaaa', 'STU', 33.20);
INSERT INTO data1(field1, field2, field3, field4) VALUES(0,'bbbbbbb', 'ABC', 24.20);
INSERT INTO data1(field1, field2, field3, field4) VALUES(0,'bbbbbbb', 'DEF', 53.20);
INSERT INTO data1(field1, field2, field3, field4) VALUES(0,'ccccccc', 'ABC', 24.20);
INSERT INTO data1(field1, field2, field3, field4) VALUES(0,'ccccccc', 'DEF', 64.20);
INSERT INTO data1(field1, field2, field3, field4) VALUES(0,'ccccccc', 'GHI', 23.20);
INSERT INTO data1(field1, field2, field3, field4) VALUES(0,'ccccccc', 'JKL', 45.20);
INSERT INTO data1(field1, field2, field3, field4) VALUES(0,'ccccccc', 'MNO', 65.20);
END
14 rows affected

EXECUTE BLOCK RETURNS (FIELD1 int, FIELD2 varchar(20), FIELD3 varchar(20), FIELD4 varchar(20), NR int)
AS
DECLARE VARIABLE old varchar(20);
BEGIN
  NR = 0;
  old = '';
  FOR SELECT FIELD1, FIELD2, FIELD3, FIELD4
      FROM DATA1
      INTO :FIELD1, :FIELD2, :FIELD3, :FIELD4 DO
  BEGIN
    IF (old <> FIELD2) THEN NR = 0;
    NR = NR + 1;
    old = FIELD2;
    if (NR < 4) THEN SUSPEND;
  END
END


FIELD1
FIELD2
FIELD3
FIELD4
NR


0
aaaaaaa
ABC
12.20
1

0
aaaaaaa
DEF
23.20
2

0
aaaaaaa
GHI
45.20
3

0
bbbbbbb
ABC
24.20
1

0
bbbbbbb
DEF
53.20
2

0
ccccccc
ABC
24.20
1

0
ccccccc
DEF
64.20
2

0
ccccccc
GHI
23.20
3

FIELD2	FIELD3	FIELD4	NR
aaaaaaa	ABC	12.20	1
aaaaaaa	DEF	23.20	2
aaaaaaa	GHI	45.20	3
bbbbbbb	ABC	24.20	1
bbbbbbb	DEF	53.20	2
ccccccc	ABC	24.20	1
ccccccc	DEF	64.20	2
ccccccc	GHI	23.20	3