**UserMapper.xml** ~~~ <!--抽取xml中出现片段最高的sql--> <sql id="baseQuery"> select * from t_user </sql> <select id="findByIdList" resultMap="userMapper"> <include refid="baseQuery"></include> <where> <!-- collection:指定要遍历的(数据|集合)对象 item: 为当前遍历的元素指定一个引用 open: 条件左半部分 close: 条件右半部分 separator:每个元素的分割符 --> <foreach collection="ids" item="id" open="u_id in (" separator="," close=")"> #{id} </foreach> </where> </select> ~~~