2018 Changelog

#### Bug Fixes:[​](#bug-fixes-1 "Direct link to Bug Fixes:")

- Fixes and performance improvements for the `LowCardinality` data type. `GROUP BY` using `LowCardinality(Nullable(...))`. Getting the values of `extremes`. Processing high-order functions. `LEFT ARRAY JOIN`. Distributed `GROUP BY`. Functions that return `Array`. Execution of `ORDER BY`. Writing to `Distributed` tables (nicelulu). Backward compatibility for `INSERT` queries from old clients that implement the `Native` protocol. Support for `LowCardinality` for `JOIN`. Improved performance when working in a single stream. [#3823](https://github.com/ClickHouse/ClickHouse/pull/3823) [#3803](https://github.com/ClickHouse/ClickHouse/pull/3803) [#3799](https://github.com/ClickHouse/ClickHouse/pull/3799) [#3769](https://github.com/ClickHouse/ClickHouse/pull/3769) [#3744](https://github.com/ClickHouse/ClickHouse/pull/3744) [#3681](https://github.com/ClickHouse/ClickHouse/pull/3681) [#3651](https://github.com/ClickHouse/ClickHouse/pull/3651) [#3649](https://github.com/ClickHouse/ClickHouse/pull/3649) [#3641](https://github.com/ClickHouse/ClickHouse/pull/3641) [#3632](https://github.com/ClickHouse/ClickHouse/pull/3632) [#3568](https://github.com/ClickHouse/ClickHouse/pull/3568) [#3523](https://github.com/ClickHouse/ClickHouse/pull/3523) [#3518](https://github.com/ClickHouse/ClickHouse/pull/3518)
- Fixed how the `select_sequential_consistency` option works. Previously, when this setting was enabled, an incomplete result was sometimes returned after beginning to write to a new partition. [#2863](https://github.com/ClickHouse/ClickHouse/pull/2863)
- Databases are correctly specified when executing DDL `ON CLUSTER` queries and `ALTER UPDATE/DELETE`. [#3772](https://github.com/ClickHouse/ClickHouse/pull/3772) [#3460](https://github.com/ClickHouse/ClickHouse/pull/3460)
- Databases are correctly specified for subqueries inside a VIEW. [#3521](https://github.com/ClickHouse/ClickHouse/pull/3521)
- Fixed a bug in `PREWHERE` with `FINAL` for `VersionedCollapsingMergeTree`. [7167bfd7](https://github.com/ClickHouse/ClickHouse/commit/7167bfd7b365538f7a91c4307ad77e552ab4e8c1)
- Now you can use `KILL QUERY` to cancel queries that have not started yet because they are waiting for the table to be locked. [#3517](https://github.com/ClickHouse/ClickHouse/pull/3517)
- Corrected date and time calculations if the clocks were moved back at midnight (this happens in Iran, and happened in Moscow from 1981 to 1983). Previously, this led to the time being reset a day earlier than necessary, and also caused incorrect formatting of the date and time in text format. [#3819](https://github.com/ClickHouse/ClickHouse/pull/3819)
- Fixed bugs in some cases of `VIEW` and subqueries that omit the database. [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/3521)
- Fixed a race condition when simultaneously reading from a `MATERIALIZED VIEW` and deleting a `MATERIALIZED VIEW` due to not locking the internal `MATERIALIZED VIEW`. [#3404](https://github.com/ClickHouse/ClickHouse/pull/3404) [#3694](https://github.com/ClickHouse/ClickHouse/pull/3694)
- Fixed the error `Lock handler cannot be nullptr.` [#3689](https://github.com/ClickHouse/ClickHouse/pull/3689)
- Fixed query processing when the `compile_expressions` option is enabled (it's enabled by default). Nondeterministic constant expressions like the `now` function are no longer unfolded. [#3457](https://github.com/ClickHouse/ClickHouse/pull/3457)
- Fixed a crash when specifying a non-constant scale argument in `toDecimal32/64/128` functions.
- Fixed an error when trying to insert an array with `NULL` elements in the `Values` format into a column of type `Array` without `Nullable` (if `input_format_values_interpret_expressions` = 1). [#3487](https://github.com/ClickHouse/ClickHouse/pull/3487) [#3503](https://github.com/ClickHouse/ClickHouse/pull/3503)
- Fixed continuous error logging in `DDLWorker` if ZooKeeper is not available. [8f50c620](https://github.com/ClickHouse/ClickHouse/commit/8f50c620334988b28018213ec0092fe6423847e2)
- Fixed the return type for `quantile*` functions from `Date` and `DateTime` types of arguments. [#3580](https://github.com/ClickHouse/ClickHouse/pull/3580)
- Fixed the `WITH` clause if it specifies a simple alias without expressions. [#3570](https://github.com/ClickHouse/ClickHouse/pull/3570)
- Fixed processing of queries with named sub-queries and qualified column names when `enable_optimize_predicate_expression` is enabled. [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/3588)
- Fixed the error `Attempt to attach to nullptr thread group` when working with materialized views. [Marek Vavruša](https://github.com/ClickHouse/ClickHouse/pull/3623)
- Fixed a crash when passing certain incorrect arguments to the `arrayReverse` function. [73e3a7b6](https://github.com/ClickHouse/ClickHouse/commit/73e3a7b662161d6005e7727d8a711b930386b871)
- Fixed the buffer overflow in the `extractURLParameter` function. Improved performance. Added correct processing of strings containing zero bytes. [141e9799](https://github.com/ClickHouse/ClickHouse/commit/141e9799e49201d84ea8e951d1bed4fb6d3dacb5)
- Fixed buffer overflow in the `lowerUTF8` and `upperUTF8` functions. Removed the ability to execute these functions over `FixedString` type arguments. [#3662](https://github.com/ClickHouse/ClickHouse/pull/3662)
- Fixed a rare race condition when deleting `MergeTree` tables. [#3680](https://github.com/ClickHouse/ClickHouse/pull/3680)
- Fixed a race condition when reading from `Buffer` tables and simultaneously performing `ALTER` or `DROP` on the target tables. [#3719](https://github.com/ClickHouse/ClickHouse/pull/3719)
- Fixed a segfault if the `max_temporary_non_const_columns` limit was exceeded. [#3788](https://github.com/ClickHouse/ClickHouse/pull/3788)

#### Improvements:[​](#improvements-1 "Direct link to Improvements:")