一条记录update一次，性能比较差，容易造成阻塞
MySQL没有提供直接的方法来实现批量更新，但可以使用case when语法来实现这个功能。

<update id="updateBatch" parameterType="list">update course<trim prefix="set" suffixOverrides=","><trim prefix="peopleId =case" suffix="end,"><foreach collection="list" item="i" index="index"><if test="i.peopleId!=null">when id=#{i.id} then #{i.peopleId}</if></foreach></trim><trim prefix=" roadgridid =case" suffix="end,"><foreach collection="list" item="i" index="index"><if test="i.roadgridid!=null">when id=#{i.id} then #{i.roadgridid}</if></foreach></trim><trim prefix="type =case" suffix="end," ><foreach collection="list" item="i" index="index"><if test="i.type!=null">when id=#{i.id} then #{i.type}</if></foreach></trim><trim prefix="unitsid =case" suffix="end," ><foreach collection="list" item="i" index="index"><if test="i.unitsid!=null">when id=#{i.id} then #{i.unitsid}</if></foreach></trim></trim>where<foreach collection="list" separator="or" item="i" index="index" >id=#{i.id}</foreach>
</update>