-- 0. 传入参数
@tablename   NVARCHAR(32)   = '',           --表名
@fieldname   NVARCHAR(32)   = '',           --字段名
@sqlstring   NVARCHAR(1024) = '',           --查询条件，不含WHERE
@results     NVARCHAR(256)  = ''  OUTPUT    --输出结果
AS

DECLARE @sql   NVARCHAR(2048);
BEGIN
    BEGIN TRAN
        SET @sql =N'SELECT @results = ' + @fieldname + ' FROM ' + @tablename;
        IF (LTRIM(RTRIM(@sqlstring))<>'' AND @sqlstring IS NOT NULL)
            SET @sql = @sql + ' WHERE ' + @sqlstring;
        ELSE
            SET @sqlstring = '';

        EXECUTE sp_executesql @sql,N'@results NVARCHAR(256) OUT',@results OUTPUT
        IF @results IS NULL OR LTRIM(RTRIM(@results)) = ''
            SELECT @results = '';
        ELSE
            SELECT @results = LTRIM(RTRIM(@results));
        IF @@ERROR <> 0
        BEGIN
            ROLLBACK TRAN
            RETURN '';
        END
        ELSE
        BEGIN
            COMMIT TRAN
            RETURN @results;
        END
END