tidb: Query returns duplicated result

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do? 执行sql : select id,task_id from $table_name where task_id in (id1,id2,id3...) ORDER BY work_time, index_id; 说明：

   • sql的长度390k (in条件数量1万多个)
   • id是主键

2. What did you expect to see? 同一条记录(主键id相同)，出现一次

3. What did you see instead? 同一条记录(主键id相同)，在返回结果中出现多次

4. What version of TiDB are you using (tidb-server -V or run select tidb_version(); on TiDB)? 5.7.10-TiDB-v2.0.0