<update id="updateRole" parameterType="com.coship.web.uc.dto.RoleParam">
        update t_role
        set 
        <if test="name != null and name !=''">
            name=#{name}
        </if>
        <if test="msg != null and msg !=''">
            ,msg=#{msg}
        </if>
        <if test="type != null and type !=''">
            ,type=#{type}
        </if>
        <if test="creator_id != null and creator_id !=''">
            ,creator_id=#{creator_id}
        </if>
        <if test="level != null and level !=''">
            ,level=#{level}
        </if>
        where id=#{id}
    </update>

<update id="updateRole" parameterType="com.coship.web.uc.dto.RoleParam">
        update t_role
        set 
        <if test="name != null and name !=''">
            name=#{name},
        </if>
        <if test="msg != null and msg !=''">
            msg=#{msg},
        </if>
        <if test="type != null and type !=''">
            type=#{type},
        </if>
        <if test="creator_id != null and creator_id !=''">
            creator_id=#{creator_id},
        </if>
        <if test="level != null and level !=''">
            level=#{level}
        </if>
        where id=#{id}
    </update>

乍一看，握草，这他妈没啥区别啊。但是仔细观察后会发现，这两个mapper的细微区别：逗号的位置不同，第一种写法代码的健壮性比较强，而第二种写法当我只传部分属性例如只传name、msg、id这三个属性的时候sql将变成：update t_role set name="武大郎"，msg="卖烧饼，被西门大官人绿", where id="1"   此时报sql语法错误，而第一种写法能巧妙避免该问题。