how to create a MySQL View to select the smallest and largest Records?

Question

i have a table contains items units details (st_items_units) like :-

id	stitems_ID	unit	stitemsu_UnitNum	unit price
1	1	u1	1	2
2	1	u2	10	20
3	1	u3	100	200
4	2	u1	1	5
5	2	u2	12	60
6	3	u1	1	10
7	4	u1	1	3
8	4	u3	12	36
9	4	u4	100	300

  

as the table every item may be have only one unit or 2 unit or 3 unit or more.

i want to create 2 view :

 

1- to select the two smallest unit (if there is one unit for the item , repeat the only one ). as this table :

stitems_ID	SmallUnit	LargeUnit	SmallUnitPrice	LargeUnitPrice	UnitNum
1	u1	u2	2	20	10
2	u1	u2	5	60	12
3	u1	u1	10	10	1
4	u1	u3	3	36	12

 

2- to select the smallest unit & the largest Unit (if there is one unit for the item , repeat the only one ). as this table :

 

stitems_ID	SmallUnit	LargeUnit	SmallUnitPrice	LargeUnitPrice	UnitNum
1	u1	u3	2	200	100
2	u1	u2	5	60	12
3	u1	u1	10	10	1
4	u1	u4	3	300	100