<!-- 1:后面跟1=1 决对成立-->
	<select id="queryPersonByidAndNo">
		select * from person where 1=1
		<if test=" id !=null and id !='' ">
			 and id = #{id}
		</if>
		<if test=" id !=null and id !='' ">
			and  no = #{no}
		</if>
	</select>
	<!-- 2 ：后面跟where标签，会将第一个and过滤（不会过滤第二个）-->
	<select id="queryPersonByidAndNo">
		select * from person where
		<where>
			<if test=" id !=null and id !='' ">
			 and id = #{id}
			</if>
			<if test=" id !=null and id !='' ">
				and  no = #{no}
			</if>
		</where>
	</select>