DECLARE @MyINT int = 0;
   declare @MyVarChar varchar(12) = NULL;
   IF @MyINT = @MyVarChar
      PRINT 'TRUE! 0 equals ''''';
   ELSE 
   PRINT 'FALSE!';
   Result:
    FALSE 

declare @MyVarChar varchar(12) = '';

declare @MyVarcharInt int

set @MyVarcharInt = @MyVarChar

select @MyVarChar MyVarchar, @MyVarcharInt MyVarcharInt

select cast('' as int)
-----------
0

SELECT TO_NUMBER('') FROM dual;
----------
(null)

' 1'
'01'

' '
'0'

''
' '

''
' '
'0'