Mybaits的去掉多余的符号问题

Question

<insert id="insertSelective" keyColumn="id" keyProperty="id" parameterType="com.second.hand.trading.server.model.IdleItemModel" useGeneratedKeys="true">
    insert into sh_idle_item
    <trim prefix="(" suffix=")" suffixOverrides=",">
      <if test="idleName != null">
        idle_name,
      </if>
      <if test="idleDetails != null">
        idle_details,
      </if>
      <if test="pictureList != null">
        picture_list,
      </if>
      <if test="idlePrice != null">
        idle_price,
      </if>
      <if test="idlePlace != null">
        idle_place,
      </if>
      <if test="idleLabel != null">
        idle_label,
      </if>
      <if test="releaseTime != null">
        release_time,
      </if>
      <if test="idleStatus != null">
        idle_status,
      </if>
      <if test="userId != null">
        user_id,
      </if>
    </trim>
    <trim prefix="values (" suffix=")" suffixOverrides=",">
      <if test="idleName != null">
        #{idleName,jdbcType=VARCHAR},
      </if>
      <if test="idleDetails != null">
        #{idleDetails,jdbcType=VARCHAR},
      </if>
      <if test="pictureList != null">
        #{pictureList,jdbcType=VARCHAR},
      </if>
      <if test="idlePrice != null">
        #{idlePrice,jdbcType=DECIMAL},
      </if>
      <if test="idlePlace != null">
        #{idlePlace,jdbcType=VARCHAR},
      </if>
      <if test="idleLabel != null">
        #{idleLabel,jdbcType=INTEGER},
      </if>
      <if test="releaseTime != null">
        #{releaseTime,jdbcType=TIMESTAMP},
      </if>
      <if test="idleStatus != null">
        #{idleStatus,jdbcType=TINYINT},
      </if>
      <if test="userId != null">
        #{userId,jdbcType=BIGINT},
      </if>
    </trim>

这个mybaits的是插入一个商品的信息，为什么要重复两次，两个trim标签的作用是什么？

Answer 1

当然需要2个了，1个是字段，1个是值。

insert into student (id,name) values(1,"张三");

其中标签，可以理解为for循环。开头(。结尾)。中间，分割。