存储过程中动态调用SQL语句

1.DECLARE @sql nvarchar(4000), -- nvarchar(MAX) on SQL 2005.
@col sysname,
@min varchar(20)
SELECT @col = N'au_fname'
SELECT @sql = N'SELECT @min = convert(varchar(20), MIN(' + @col +
N')) FROM authors'
EXEC sp_executesql @sql, N'@min varchar(20) OUTPUT', @min OUTPUT
SELECT @min