title: how to solve parameter in sp_executesql
body: <p>I have the following query:</p>
  
  <pre><code>create proc [dbo].GetCustById
  as
  DECLARE @sql nvarchar(500)
  DECLARE @Param  nvarchar(200)
  SET @sql = 'select @columnName from customer where custId = @custId'
  SET @Param = N'@columnName varchar(10), @custId int'
  
  EXEC sp_executesql @sql, @Param , @columnName = 'Address1', @custId = '42'
  </code></pre>
  
  <p>But it always return a string "Address1" instead of the value of Address1 column. Anyone can help?</p>
  
  <p>thanks</p>