Problems with SQL Merge time period

Suppose the table structure looks like this:

Tsheets
Field name	Field type	Constraints
Id	CHAR (10)	PRIMARY KEY
Start_date	DATE	CHECK (start_date<= end_date)
End_date	DATE

Enter as:
1, ' 1997-01-01 ', ' 1997-01-03 '
2, ' 1997-01-02 ', ' 1997-01-04 '
3, ' 1997-01-04 ', ' 1997-01-05 '
4, ' 1997-01-06 ', ' 1997-01-09 '
5, ' 1997-01-09 ', ' 1997-01-09 '
6, ' 1997-01-09 ', ' 1997-01-09 '
7, ' 1997-01-12 ', ' 1997-01-15 '
8, ' 1997-01-13 ', ' 1997-01-14 '
9, ' 1997-01-14 ', ' 1997-01-14 '
10, ' 1997-01-17 ', ' 1997-01-17 '
The output is:
Start_date end_date
1997-01-01 1997-01-05
1997-01-06 1997-01-09
1997-01-12 1997-01-15
1997-01-17 1997-01-17

1     SELECTX.start_date,MIN(x.end_date) asend_date2        from(SELECTt1.start_date,t2.end_date3              fromTsheets asT1,tsheets asT2,tsheets asT3WHERET1.end_date<=T2.end_dateGROUP  byt1.start_date,t2.end_date4              having MAX( Case5                when(t1.start_date>t3.start_date6                  andT1.start_date<=t3.end_date)7                 OR(t2.end_date>=t3.start_date8                  andT2.end_date<t3.end_date)9                  Then 1 ELSE 0 END)= 0) asXTen        GROUP  byX.start_date

Problems with SQL Merge time period