String Comparison process on Sqlite

select * from x where date <= x

Test case:

//String....................

str1 = "12/10/2015";

str2 = "08/10/2015";

str3 = "8/10/2015";

str4 = "8";

str5 = "8/"

str6 = "80"

str1 <= str2  ans: false

str1 <= str3  ans: true

str1 <= str4  ans: false

str1 <= str5  ans: true

str1 <= str6  ans: false

Can any one explain this String comparison? I tried this on SQLITE and got those answer, but confused about how string is comparing here.