解決問題：insert後需要用到自動生成的主鍵"id"

解決方法：

    <!-- 直接寫到insert語句中 -->
    <selectKey resultType="java.lang.Integer" order="AFTER" keyProperty="id">
              SELECT LAST_INSERT_ID()
    </selectKey>

使用示例：

<insert id="insertSelective" parameterType="po.TTask">
    <selectKey resultType="java.lang.Integer" order="AFTER" keyProperty="id">
          SELECT LAST_INSERT_ID()
    </selectKey>
    insert into t_task
    <trim prefix="(" suffix=")" suffixOverrides=",">
      <if test="id != null">
        id,
      </if>
      <if test="username != null">
        username,
      </if>
      <if test="stat != null">
        stat,
      </if>
      <if test="ts != null">
        ts,
      </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="stat != null">
        #{stat,jdbcType=INTEGER},
      </if>
      <if test="ts != null">
        #{ts,jdbcType=TIMESTAMP},
      </if>
    </trim>
  </insert>