Why is Biot-Savart Law Zero for Cylinderical Uniform Current Density?

[hokhani]

if you want to calculate the magnetic field of a cylinderical uniform current density
by Biot-savart law,
it will be zero, but by Ampere law it is not zero?
why?
please guide me

 

[Meir Achuz]

if you want to calculate the magnetic field of a cylinderical uniform current density
by Biot-savart law,
it will be zero,

Why do you say that?

 

[hokhani]

oh sorry
I made a mistake