[基础] 从字符串转换为smalldatetime数据类型时发生语法错误

我现在用数据环境设计器打印，语句为
select * from orderbooks where order_date >= '" + Str(DTPicker1.Value) + "'and  order_date<='" + Str(DTPicker2.Value) + "'and yw_memo is null order by bm_code
出现错误
“从字符串转换为smalldatetime数据类型时发生语法错误”
帮忙看看哪错了，谢谢