1.mapper多参数语句：

select * from table where age= #{age}

<if test="uname !=null and uname !=' ' ">  //判断非空

and uname like concat ( concat('%',#{uname}),'%') //like语句

</if>

2.foreach语句：

接口：public List<book> get(@Param("isbns") Set<String> isbns) throws Exception;

mapper语句：<select id="get" resultType="book">

select isbn, bname ,press from book where isbn in

<foreach item="isbn" index="index" collection="isbns" open="(" separator="," close=")">

#{isbn}

</>

3.语义冲突

//错误提示：The content of elements must consist of well-formed character data or markup. <= 是和等左边的符号冲突，需要用 进行转义

<![CDATA[ and buytime <= #{endDate} ]]>