SQL & PL/SQL :: Number Of Years Calculation

for making the query for following data,when we give start and end date then query need to calculate number of years.

if less than one year then return 0
if exact one year then return 1
if exact 1.5 years (18 months) then return 2
if exact 2 years (24 months) then also return 2
if exact 2.5 years (30 months) then return 3
if exact 3 years (36 months) then also return 3
if exact 3.5 years (42 months) then return 4
if exact 4 years (48 months) then also return 4
and so.

also we need to add leap year 1 day if exist in start and end date.

YearSalary
11
1.52
22
2.53
33
3.54
44
4.55
55
[code]....