Oracle 11g Release 2

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with YourTable ( FILE_NUM, START_DATE, END_DATE ) as (
select 1111, to_date( 'Apr. 04, 1977', 'Mon. DD, YYYY', 'nls_date_language = english' ), to_date( 'Jun. 30, 1984', 'Mon. DD, YYYY', 'nls_date_language = english' ) from dual 
union all
select 1112, to_date( 'Jan. 03, 1987', 'Mon. DD, YYYY', 'nls_date_language = english' ), to_date( 'Sep. 05, 2010', 'Mon. DD, YYYY', 'nls_date_language = english' ) from dual 
union all
select 1113, to_date( 'May. 14, 1962', 'Mon. DD, YYYY', 'nls_date_language = english' ), to_date( 'Jan. 30, 1998', 'Mon. DD, YYYY', 'nls_date_language = english' ) from dual 
union all
select 1114, to_date( 'Oct. 09, 2001', 'Mon. DD, YYYY', 'nls_date_language = english' ), to_date( 'Aug. 22, 2025', 'Mon. DD, YYYY', 'nls_date_language = english' ) from dual 
union all
select 1115, to_date( 'Nov. 18, 2003', 'Mon. DD, YYYY', 'nls_date_language = english' ), to_date( 'Aug. 22, 2028', 'Mon. DD, YYYY', 'nls_date_language = english' ) from dual
)
SELECT dec_start, dec_end, COUNT(*) nb
FROM (
    SELECT t.*, level
        ,   10 * trunc( extract ( year from (START_DATE) ) / 10 ) + 10 * LEVEL - 10 dec_start
        ,   10 * trunc( extract ( year from (START_DATE) ) / 10 ) + 10 * LEVEL - 1 dec_end
    FROM YourTable T
    CONNECT BY 
        10 * TRUNC( EXTRACT ( YEAR FROM (START_DATE) ) / 10 ) + 10 * LEVEL - 10 
            <   10 * CEIL( EXTRACT ( YEAR FROM (END_DATE) ) / 10 )
    AND PRIOR FILE_NUM = FILE_NUM
    AND PRIOR START_DATE = START_DATE
    AND PRIOR END_DATE = END_DATE
    AND PRIOR SYS_GUID() IS NOT NULL
)
group by dec_start, dec_end 
order by dec_start, dec_end
;

DEC_START	DEC_END	NB
1960	1969	1
1970	1979	2
1980	1989	3
1990	1999	2
2000	2009	3
2010	2019	2
2020	2029	2