How to reference numeric variables in dynamic SQL statements

CodeAs follows:
Declare @ uid int;
Set @ uid = 7;

Declare @ SQL nvarchar (1000 );
Set @ SQL = 'select * from [AAA] Where uid = '@ uid
Exec (@ SQL)

Prompt
Message 245, level 16, state 1, 9th rows
Failed to convert varchar value 'select * from [AAA] Where uid = 'to data type Int.

If I define @ UID as varchar, there will be no problem. How can this problem be solved? Thank you!

Declare @ uid int;
Set @ uid = 7;

Declare @ SQL nvarchar (1000 );
Set @ SQL = 'select * from [AAA] Where uid = 'rtrim (@ UID)
Exec (@ SQL)

Declare @ uid int
Set @ uid = 7

Declare @ SQL nvarchar (1000)
Set @ SQL = 'select * from [AAA] Where uid = 'Cast (@ UID as nvarchar)
Exec (@ SQL)

Declare @ uid int;
Set @ uid = 7;

Declare @ SQL nvarchar (1000 );
Set @ SQL = n' select * from [AAA] Where uid = @ uid'
Exec sp_executesql @ SQL, n' @ uid int', @ uid