CHANGELOG: add release notes for v2.1.7 (#9916)

CHANGELOG.md

@@ -1,6 +1,22 @@
 # TiDB Changelog
 All notable changes to this project will be documented in this file. See also [Release Notes](https://github.com/pingcap/docs/blob/master/releases/rn.md), [TiKV Changelog](https://github.com/tikv/tikv/blob/master/CHANGELOG.md) and [PD Changelog](https://github.com/pingcap/pd/blob/master/CHANGELOG.md).
 
+## [2.1.7] 2019-03-27
+
+* Fix the issue of longer startup time when upgrading the program caused by canceling DDL operations [#9768](https://github.com/pingcap/tidb/pull/9768)
+* Fix the issue that the `check-mb4-value-in-utf8` configuration item is in the wrong position in the `config.example.toml` file [#9852](https://github.com/pingcap/tidb/pull/9852)
+* Improve the compatibility of the `str_to_date` built-in function with MySQL [#9817](https://github.com/pingcap/tidb/pull/9817)
+* Fix the compatibility issue of the `last_day` built-in function [#9750](https://github.com/pingcap/tidb/pull/9750)
+* Add the `tidb_table_id` column for `infoschema.tables` to facilitate getting `table_id` by using SQL statements and add the `tidb_indexes` system table to manage the relationship between Table and Index [#9862](https://github.com/pingcap/tidb/pull/9862)
+* Add a check about the null definition of Table Partition [#9663](https://github.com/pingcap/tidb/pull/9663)
+* Change the privileges required by `Truncate Table` from `Delete` to `Drop` to make it consistent with MySQL [#9876](https://github.com/pingcap/tidb/pull/9876)
+* Support using subqueries in the `DO` statement [#9877](https://github.com/pingcap/tidb/pull/9877) 
+* Fix the issue that the `default_week_format` variable does not take effect in the `week` function [#9753](https://github.com/pingcap/tidb/pull/9753) 
+* Support the plugin framework [#9880](https://github.com/pingcap/tidb/pull/9880), [#9888](https://github.com/pingcap/tidb/pull/9888) 
+* Support checking the enabling state of binlog by using the `log_bin` system variable [#9634](https://github.com/pingcap/tidb/pull/9634) 
+* Support checking the Pump/Drainer status by using SQL statements [#9896](https://github.com/pingcap/tidb/pull/9896) 
+* Fix the compatibility issue about checking mb4 character on utf8 when upgrading TiDB [#9887](https://github.com/pingcap/tidb/pull/9887) 
+
 ## [2.1.6] 2019-03-15
 
 ### SQL Optimizer/Executor