ektravel commented on code in PR #15173: URL: https://github.com/apache/druid/pull/15173#discussion_r1379154923
########## docs/do-not-merge.md: ########## @@ -0,0 +1,815 @@ +<!--Intentionally, there's no Apache license so that the GHA fails it. This file is not meant to be merged. +--> + +Apache Druid 28.0.0 contains over $NUMBER_FEATURES new features, bug fixes, performance enhancements, documentation improvements, and additional test coverage from $NUMBER_OF_CONTRIBUTORS contributors. + +See the [complete set of changes](https://github.com/apache/druid/issues?q=is%3Aclosed+milestone%3A28.0+sort%3Aupdated-desc+) for additional details, including bug fixes. + +Review the [upgrade notes](#upgrade-notes) and [incompatible changes](#incompatible-changes) before you upgrade to Druid 28.0.0. + +# Important changes and deprecations + +In Druid 28.0.0, we have made substantial improvements to querying to make the system more ANSI SQL compatible. This includes changes in handling NULL and boolean values as well as boolean logic. At the same time, the Apache Calcite library has been upgraded to the latest version. While we have documented known query behavior changes, please read the [upgrade notes](#upgrade-notes) section carefully. Test your application before rolling out to broad production scenarios while closely monitoring the query status. + +## SQL compatibility + +Druid continues to make SQL query execution more consistent with how standard SQL behaves. However, there are feature flags available to restore the old behavior if needed. + +### Three-valued logic + +Druid native filters now observe SQL [three-valued logic](https://en.wikipedia.org/wiki/Three-valued_logic#SQL) (`true`, `false`, or `unknown`) instead of Druid's classic two-state logic when you set the following configuration values: + +* `druid.generic.useThreeValueLogicForNativeFilters = true` +* `druid.expressions.useStrictBooleans = true` +* `druid.generic.useDefaultValueForNull = false` + +[#15058](https://github.com/apache/druid/pull/15058) + +### Strict booleans + +`druid.expressions.useStrictBooleans` is now enabled by default. +Druid now handles booleans strictly using `1` (true) or `0` (false). +Previously, true and false could be represented either as `true` and `false` as well as `1` and `0`, respectively. +In addition, Druid now returns a null value for Boolean comparisons like `True && NULL`. + +If you don't explicitly configure this property in `runtime.properties`, clusters now use LONG types for any ingested boolean values and in the output of boolean functions for transformations and query time operations. + +This change may impact your query results. For more information, see [SQL compatibility in the upgrade notes](#sql-compatibility-1). + +[#14734](https://github.com/apache/druid/pull/14734) + +### NULL handling + +`druid.generic.useDefaultValueForNull` is now disabled by default. +Druid now differentiates between empty records and null records. +Previously, Druid might treat empty records as empty or null. + +This change may impact your query results. For more information, see [SQL compatibility in the upgrade notes](#sql-compatibility-1). + +[#14792](https://github.com/apache/druid/pull/14792) + +## SQL planner improvements + +Druid uses Apache Calcite for SQL planning and optimization. Starting in Druid 28.0.0, the Calcite version has been upgraded from 1.21 to 1.35. This upgrade brings in many bug fixes in SQL planning from Calcite. As part of the upgrade, the behavior of type inference for [dynamic parameters](#dynamic-parameters) and the [recommended syntax for UNNEST](#new-syntax-for-sql-unnest) have changed. Review Comment: @clintropolis Since the updated recommendation for unnest isn't directly related to the calcite upgrade, I think we should move to "SQL UNNEST and ingestion flattening". -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
