Oracle 11g Release 2

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create table test_table as
    select 10 as min, 121 as max from dual union all
    select 122 as min, 648 as max from dual union all
    select 1200 as min, 1599 as max from dual
    
    
3 rows affected

create table reference_table as
    select 50 as min, 106 as max from dual union all
    select 200 as min, 1400 as max from dual union all
    select 1450 as min, 1500 as max from dual
3 rows affected

with vals as (
      select min as x, 1 as inc, 0 as is_ref
      from test_table
      union all
      select max + 1, -1 as inc, 0 as is_ref
      from test_table
      union all
      select min as x, 0, 1 as is_ref
      from reference_table
      union all
      select max + 1 as x, 0, -1 as is_ref
      from reference_table
     )
select *
from (select refgrp, incgrp, ref, inc2, min(x) as min, (lead(min(x), 1, max(x) + 1) over (order by min(x))  - 1) as max
from (select v.*,
            row_number() over (order by x) - row_number() over (partition by ref order by x) as refgrp,
            row_number() over (order by x) - row_number() over (partition by inc2 order by x) as incgrp
      from (select v.*, sum(is_ref) over (order by x, inc) as ref,
                   sum(inc) over (order by x, inc) as inc2
            from vals v
           ) v
     ) v
group by refgrp, incgrp, ref, inc2
) v
where ref = 0 and inc2 = 1
order by min



REFGRP
INCGRP
REF
INC2
MIN
MAX


0
0
0
1
10
49

1
0
0
1
107
121

2
1
0
1
122
121

4
2
0
1
1401
1449

5
2
0
1
1501
1599


with vals as (
      select min as x, 1 as inc, 0 as is_ref
      from test_table
      union all
      select max + 1, -1 as inc, 0 as is_ref
      from test_table
      union all
      select min as x, 0, 1 as is_ref
      from reference_table
      union all
      select max + 1 as x, 0, -1 as is_ref
      from reference_table
     )


      select v.*,
            row_number() over (order by x, inc ) - row_number() over (partition by ref order by x, inc ) as refgrp,
            row_number() over (order by x, inc ) - row_number() over (partition by inc2 order by x, inc ) as incgrp
      from (select v.*, sum(is_ref) over (order by x, inc) as ref,
                   sum(inc) over (order by x, inc) as inc2
            from vals v
           ) v
order by x



X
INC
IS_REF
REF
INC2
REFGRP
INCGRP


10
1
0
0
1
0
0

50
0
1
1
1
1
0

107
0
-1
0
1
1
0

122
-1
0
0
0
1
3

122
1
0
0
1
1
1

200
0
1
1
1
4
1

649
-1
0
1
0
4
5

1200
1
0
1
1
4
2

1401
0
-1
0
1
4
2

1450
0
1
1
1
5
2

1501
0
-1
0
1
5
2

1600
-1
0
0
0
5
9
X	INC	IS_REF	REF	INC2	REFGRP	INCGRP
10	1	0	0	1	0	0
50	0	1	1	1	1	0
107	0	-1	0	1	1	0
122	-1	0	0	0	1	3
122	1	0	0	1	1	1
200	0	1	1	1	4	1
649	-1	0	1	0	4	5
1200	1	0	1	1	4	2
1401	0	-1	0	1	4	2
1450	0	1	1	1	5	2
1501	0	-1	0	1	5	2
1600	-1	0	0	0	5	9