Mybatis动态SQL trim

<insert id="insertSelective" parameterType="com.geo.entity.SysUser">    insert into sys_user    <trim prefix="(" suffix=")" suffixOverrides=",">      <if test="id != null">        id,      </if>      <if test="userName != null">        user_name,      </if>      <if test="userPassword != null">        user_password,      </if>      <if test="userEmail != null">        user_email,      </if>      <if test="userInfo != null">        user_info,      </if>    </trim>    <trim prefix="values (" suffix=")" suffixOverrides=",">      <if test="id != null">        #{id,jdbcType=INTEGER},      </if>      <if test="userName != null">        #{userName,jdbcType=VARCHAR},      </if>      <if test="userPassword != null">        #{userPassword,jdbcType=VARCHAR},      </if>      <if test="userEmail != null">        #{userEmail,jdbcType=VARCHAR},      </if>      <if test="userInfo != null">        #{userInfo,jdbcType=VARCHAR},      </if>    </trim>  </insert>

trim 标签有四个属性：
prefix: 增加的前缀
prefixOverrides:删除指定的前缀
suffix:增加指定后缀
suffixOverrides:删除指定后缀

where标签，和set标签都是通过trim标签实现的!