2020 Changelog

#### New Feature[​](#new-feature-2 "Direct link to New Feature")

- Background data recompression. Add the ability to specify `TTL ... RECOMPRESS codec_name` for MergeTree table engines family. [#14494](https://github.com/ClickHouse/ClickHouse/pull/14494) ([alesapin](https://github.com/alesapin)).
- Add parallel quorum inserts. This closes [#15601](https://github.com/ClickHouse/ClickHouse/issues/15601). [#15601](https://github.com/ClickHouse/ClickHouse/pull/15601) ([Latysheva Alexandra](https://github.com/alexelex)).
- Settings for additional enforcement of data durability. Useful for non-replicated setups. [#11948](https://github.com/ClickHouse/ClickHouse/pull/11948) ([Anton Popov](https://github.com/CurtizJ)).
- When duplicate block is written to replica where it does not exist locally (has not been fetched from replicas), don't ignore it and write locally to achieve the same effect as if it was successfully replicated. [#11684](https://github.com/ClickHouse/ClickHouse/pull/11684) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Now we support `WITH <identifier> AS (subquery) ...`  to introduce named subqueries in the query context. This closes [#2416](https://github.com/ClickHouse/ClickHouse/issues/2416). This closes [#4967](https://github.com/ClickHouse/ClickHouse/issues/4967). [#14771](https://github.com/ClickHouse/ClickHouse/pull/14771) ([Amos Bird](https://github.com/amosbird)).
- Introduce `enable_global_with_statement` setting which propagates the first select's `WITH` statements to other select queries at the same level, and makes aliases in `WITH` statements visible to subqueries. [#15451](https://github.com/ClickHouse/ClickHouse/pull/15451) ([Amos Bird](https://github.com/amosbird)).
- Secure inter-cluster query execution (with initial\_user as current query user). [#13156](https://github.com/ClickHouse/ClickHouse/pull/13156) ([Azat Khuzhin](https://github.com/azat)). [#15551](https://github.com/ClickHouse/ClickHouse/pull/15551) ([Azat Khuzhin](https://github.com/azat)).
- Add the ability to remove column properties and table TTLs. Introduced queries `ALTER TABLE MODIFY COLUMN col_name REMOVE what_to_remove` and `ALTER TABLE REMOVE TTL`. Both operations are lightweight and executed at the metadata level. [#14742](https://github.com/ClickHouse/ClickHouse/pull/14742) ([alesapin](https://github.com/alesapin)).
- Added format `RawBLOB`. It is intended for input or output a single value without any escaping and delimiters. This closes [#15349](https://github.com/ClickHouse/ClickHouse/issues/15349). [#15364](https://github.com/ClickHouse/ClickHouse/pull/15364) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Add the `reinterpretAsUUID` function that allows to convert a big-endian byte string to UUID. [#15480](https://github.com/ClickHouse/ClickHouse/pull/15480) ([Alexander Kuzmenkov](https://github.com/akuzm)).
- Implement `force_data_skipping_indices` setting. [#15642](https://github.com/ClickHouse/ClickHouse/pull/15642) ([Azat Khuzhin](https://github.com/azat)).
- Add a setting `output_format_pretty_row_numbers` to numerate the result in Pretty formats. This closes [#15350](https://github.com/ClickHouse/ClickHouse/issues/15350). [#15443](https://github.com/ClickHouse/ClickHouse/pull/15443) ([flynn](https://github.com/ucasFL)).
- Added query obfuscation tool. It allows to share more queries for better testing. This closes [#15268](https://github.com/ClickHouse/ClickHouse/issues/15268). [#15321](https://github.com/ClickHouse/ClickHouse/pull/15321) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Add table function `null('structure')`. [#14797](https://github.com/ClickHouse/ClickHouse/pull/14797) ([vxider](https://github.com/Vxider)).
- Added `formatReadableQuantity` function. It is useful for reading big numbers by human. [#14725](https://github.com/ClickHouse/ClickHouse/pull/14725) ([Artem Hnilov](https://github.com/BooBSD)).
- Add format `LineAsString` that accepts a sequence of lines separated by newlines, every line is parsed as a whole as a single String field. [#14703](https://github.com/ClickHouse/ClickHouse/pull/14703) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)), [#13846](https://github.com/ClickHouse/ClickHouse/pull/13846) ([hexiaoting](https://github.com/hexiaoting)).
- Add `JSONStrings` format which output data in arrays of strings. [#14333](https://github.com/ClickHouse/ClickHouse/pull/14333) ([hcz](https://github.com/hczhcz)).
- Add support for "Raw" column format for `Regexp` format. It allows to simply extract subpatterns as a whole without any escaping rules. [#15363](https://github.com/ClickHouse/ClickHouse/pull/15363) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Allow configurable `NULL` representation for `TSV` output format. It is controlled by the setting `output_format_tsv_null_representation` which is `\N` by default. This closes [#9375](https://github.com/ClickHouse/ClickHouse/issues/9375). Note that the setting only controls output format and `\N` is the only supported `NULL` representation for `TSV` input format. [#14586](https://github.com/ClickHouse/ClickHouse/pull/14586) ([Kruglov Pavel](https://github.com/Avogar)).
- Support Decimal data type for `MaterializeMySQL`. `MaterializeMySQL` is an experimental feature. [#14535](https://github.com/ClickHouse/ClickHouse/pull/14535) ([Winter Zhang](https://github.com/zhang2014)).
- Add new feature: `SHOW DATABASES LIKE 'xxx'`. [#14521](https://github.com/ClickHouse/ClickHouse/pull/14521) ([hexiaoting](https://github.com/hexiaoting)).
- Added a script to import (arbitrary) git repository to ClickHouse as a sample dataset. [#14471](https://github.com/ClickHouse/ClickHouse/pull/14471) ([alexey-milovidov](https://github.com/alexey-milovidov)).
- Now insert statements can have asterisk (or variants) with column transformers in the column list. [#14453](https://github.com/ClickHouse/ClickHouse/pull/14453) ([Amos Bird](https://github.com/amosbird)).
- New query complexity limit settings `max_rows_to_read_leaf`, `max_bytes_to_read_leaf` for distributed queries to limit max rows/bytes read on the leaf nodes. Limit is applied for local reads only, *excluding* the final merge stage on the root node. [#14221](https://github.com/ClickHouse/ClickHouse/pull/14221) ([Roman Khavronenko](https://github.com/hagen1778)).
- Allow user to specify settings for `ReplicatedMergeTree*` storage in `<replicated_merge_tree>` section of config file. It works similarly to `<merge_tree>` section. For `ReplicatedMergeTree*` storages settings from `<merge_tree>` and `<replicated_merge_tree>` are applied together, but settings from `<replicated_merge_tree>` has higher priority. Added `system.replicated_merge_tree_settings` table. [#13573](https://github.com/ClickHouse/ClickHouse/pull/13573) ([Amos Bird](https://github.com/amosbird)).
- Add `mapPopulateSeries` function. [#13166](https://github.com/ClickHouse/ClickHouse/pull/13166) ([Ildus Kurbangaliev](https://github.com/ildus)).
- Supporting MySQL types: `decimal` (as ClickHouse `Decimal`) and `datetime` with sub-second precision (as `DateTime64`). [#11512](https://github.com/ClickHouse/ClickHouse/pull/11512) ([Vasily Nemkov](https://github.com/Enmk)).
- Introduce `event_time_microseconds` field to `system.text_log`, `system.trace_log`, `system.query_log` and `system.query_thread_log` tables. [#14760](https://github.com/ClickHouse/ClickHouse/pull/14760) ([Bharat Nallan](https://github.com/bharatnc)).
- Add `event_time_microseconds` to `system.asynchronous_metric_log` & `system.metric_log` tables. [#14514](https://github.com/ClickHouse/ClickHouse/pull/14514) ([Bharat Nallan](https://github.com/bharatnc)).
- Add `query_start_time_microseconds` field to `system.query_log` & `system.query_thread_log` tables. [#14252](https://github.com/ClickHouse/ClickHouse/pull/14252) ([Bharat Nallan](https://github.com/bharatnc)).

#### Bug Fix[​](#bug-fix-9 "Direct link to Bug Fix")