Varchar and nvarchar are different. Careful Error

Today's call Program Always reports an error when executing SQL statements. The final result is varchar and nvarchar. Depressed.
This problem is not solved, but the character string passed by the API user is incorrectly encoded, leading to garbled characters. Create   Table   [ Test ] (
[ Nn ]   [ Varchar ] ( 50 ) Collate chinese_prc_ci_as Not   Null ,
Constraint   [ Pk_test ]   Primary   Key Clustered  
(
[ Nn ]
) On   [ Primary ]  
) On   [ Primary ]
Go

Select   *   From Test

Insert   Into Test (NN)
Values (N ' BSS? Why? § ID ' )

Insert   Into Test (NN)
Values (N ' BSS zookeeper» § ID ' )
/**/ /*
Server: Message 2627, Level 14, status 1, Row 1
The primary key constraint 'pk _ test' is violated '. Duplicate keys cannot be inserted in the object 'test.
The statement has been terminated.

*/

Declare   @ S   Nvarchar ( 50 )
, @ S2   Nvarchar ( 50 )

Select   @ S   = N ' BSS? Why? § ID ' , @ S2   = N ' BSS zookeeper» § ID '

Select   1   Where   @ S = @ S2

Select   1   Where N ' BSS? Why? § ID ' = N ' BSS zookeeper» § ID '
/**/ /*

(The number of affected rows is 0)


(The number of affected rows is 0)
*/

Declare   @ S   Varchar ( 50 )
, @ S2   Varchar ( 50 )

Select   @ S   = N ' BSS? Why? § ID ' , @ S2   = N ' BSS zookeeper» § ID '

Select   1   Where   @ S = @ S2

Select   1   Where N ' BSS? Why? § ID ' = N ' BSS zookeeper» § ID '
/**/ /*

(The number of affected rows is 1)


(The number of affected rows is 0)

*/