Oracle 18c

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create table t as
     select 340 as column1, 9870 as column2, 'abc' as column3, 'mno' as column4 from dual union all
     select 338 as column1, 9870 as column2, 'abc' as column3, 'mno' as column4 from dual union all
     select 337 as column1, 3456 as column2, 'abc' as column3, 'mno' as column4 from dual union all
     select 336 as column1, 3456 as column2, 'abc' as column3, 'mno' as column4 from dual union all
     select 335 as column1, 3456 as column2, 'abc' as column3, 'mno' as column4 from dual union all
     select 334 as column1, 3456 as column2, 'abc' as column3, 'mno' as column4 from dual union all
     select 332 as column1, 3456 as column2, 'abc' as column3, 'mno' as column4 from dual union all
     select 331 as column1, 3456 as column2, 'abc' as column3, 'mno' as column4 from dual union all
     select 252 as column1, 2132 as column2, 'abc' as column3, 'mno' as column4 from dual union all
     select 251 as column1, 2132 as column2, 'abc' as column3, 'mno' as column4 from dual union all
     select 249 as column1, 2132 as column2, 'abc' as column3, 'mno' as column4 from dual

11 rows affected

COLUMN1	COLUMN2	COLUMN3	COLUMN4	PREV_COLUMN1	GRP	COLUMN5
340	9870	abc	mno	338	4	1
338	9870	abc	mno	337	3	5
337	3456	abc	mno	336	3	4
336	3456	abc	mno	335	3	3
335	3456	abc	mno	334	3	2
334	3456	abc	mno	332	3	1
332	3456	abc	mno	331	2	4
331	3456	abc	mno	252	2	3
252	2132	abc	mno	251	2	2
251	2132	abc	mno	249	2	1
249	2132	abc	mno	null	1	1