当使用Map做为参数和pojo作参数时，两者配置文件写法相同

     <select id="SelectifwhereTestMap" parameterType="map" resultType="user">
    select * from user
    <where>
    <if test="username!=null and username!=''">
    and username like '%${username}%' 
    </if>
    
    <if test="sex!=null and sex!=''">
    and sex=#{sex} 
    </if>
    
    <if test="address!=null and address!=''">
    and address like '%${address}%' 
    </if>
    </where><!--where可以去除第一个空格或者OR-->
    </select> 
    ```

<select id="SelectifwhereTestUser" parameterType="user" resultType="user">
select * from user
<where><!--where可以去除第一个空格或者OR-->
<if test="username!=null and username!=''">
and username like '%${username}%' 
</if>

<if test="sex!=null and sex!=''">
and sex=#{sex} 
</if>

<if test="address!=null and address!=''">
and address like '%${address}%' 
</if>
</where>
</select>