SELECT .... WHERE something equals with Chinese characters

In a C# window application, when I do

select * from myTable where category = '牛奶'

or

select * from myTable where category = 'baby牛奶'

The result does not return any rows.

But

select * from myTable where category = 'baby'

This result returns some rows. Could anyone tell me why please?

Note: in myTable, some category of column has some values with 牛奶 or baby牛奶, and I have no problems displaying Chinese characters on the window application.

牛奶 are Chinese characters.