Aleksey Plekhanov created IGNITE-23745:
------------------------------------------
Summary: Calcite engine. Add ability to extent SQL engine with new
system functions/operators
Key: IGNITE-23745
URL: https://issues.apache.org/jira/browse/IGNITE-23745
Project: Ignite
Issue Type: Improvement
Reporter: Aleksey Plekhanov
Assignee: Aleksey Plekhanov
Old H2-based SQL engine has a lot of functions and operators, which are
currently not supported by Calcite-based SQL engine. Some of these
functions/operators have another syntax and duplicating it just to provide
compatibility is not a good idea. For example, there is a function {{SUBSTR(a,
b, c)}}, supported by H2-engine and not supported by Calcite-engine. Instead
Calcite-engine supports {{SUBSTRING}} function (also described by SQL
standard). Adding {{SUBSTR}} to the Calcite-engine will lead to overloading
functions list with duplicates. User defined functions can't fully cover all
features that Calcite has to implement system functions. So, it's proposed to
add an ability to implement new system functions by plugins or extensions.
I see several points of extension on different stages of query execution:
* {{IgniteStdSqlOperatorTable}} - a table of operators which can be used by SQL
engine. We already have public method {{register}} here.
* {{IgniteSqlCallRewriteTable}} - a table of rewriters for operators (before
validation, SqlNode to SqlNode). We already have public methid {{register}}
here too.
* IgniteConvertletTable - a table of convertlet (validated SqlNode to RexNode).
Protected methods {{registerOp}} and {{addAlias}} can be converted to public.
* {{RexImpTable}} - a table of implementors (RexNode to Expression). Here we
have some private methods (all they just register implementor in {{map}}), and
a set of predefined implementors, some of them can be converted to public.
* {{Accumulators}} - a table of aggregate functions. Refactoring required here.
Currently the list of aggregate functions is hardcoded with switch/case block.
(Perhaps we can fix {{Accumulators}} by another ticket).
Also, it will be useful to somehow extend grammer, but I see no simple way how
to do it right now.
--
This message was sent by Atlassian Jira
(v8.20.10#820010)
