If you'll accept a decimal, then it's .0123456789
If you want whole numbers only, and you'll accept a leading zero, then it's 0,123,456,789.
If not, then it's 1,023,456,789.
1,234,567
The smallest 4-digit number without any repeated digits is 1023, as it starts with the smallest possible digit (1) followed by the next smallest digits (0, 2, 3). The largest 4-digit number without any repeated digits is 9876, which uses the largest digits available in descending order.
5
5
none
0132 or 1234 0123 or without 0 at front = 1023
The smallest number with no digits repeated would either be zero or one, depending on the set of numbers you want to choose from.
102
10234567
1023456789
0123456789
123456.