mybatis update语句 返回值为null

解决方案：检查xml中对应的sql语句，标签不是select而是update
错误写法：

    <select id="lockSkuStock" resultType="java.lang.Long">
        update wms_ware_sku
        set stock_locked = stock_locked + #{num}
        where sku_id = #{skuId}
          and ware_id = #{wareId}
          and stock - stock_locked > 0
    </select>

控制台输出：null

修改为：

    <update id="lockSkuStock">
        update wms_ware_sku
        set stock_locked = stock_locked + #{num}
        where sku_id = #{skuId}
          and ware_id = #{wareId}
          and stock - stock_locked > 0
    </update>