annagobova commented on code in PR #10983: URL: https://github.com/apache/ignite/pull/10983#discussion_r1358039586
########## docs/_docs/SQL/sql-calcite.adoc: ########## @@ -241,3 +228,150 @@ Below are the data types supported by the Calcite-based SQL engine: |`java.lang.Object` |=== + +== Optimizer hints [[hints]] + +The query optimizer does its best to build the fastest excution plan. But it is a far way to create an optimizer which +is the most effective for each case. You may have better knowledge of your data design, application design or data +distribution in the cluster. The SQL hints can help the optimizer to make optimizations more rationally or build +execution plan faster. + +[NOTE] +==== +SQL hints are not mandatory to apply and might be skipped in some cases. +==== + +=== Hints format +Sql hints are defined with the special comment +++/*+ HINT */+++ reffered as _hint block_. Spaces before and after the +hint name are required. Hint block is placed right after a relation operator. Usually, after _SELECT_. Several hint +blocks for one relation operator *are not allowed*. + +Example: +[source, SQL] +---- +SELECT /*+ NO_INDEX */ T1.* FROM TBL1 where T1.V1=? and T1.V2=? +---- + +It is allowed to define several hints for the same relation operator. For that, hints are separated with comma +(spaces are optional). + +Example: +[source, SQL] +---- +SELECT /*+ NO_INDEX, EXPAND_DISTINCT_AGG */ SUM(DISTINCT V1), AVG(DISTINCT V2) FROM TBL1 GROUP BY V3 WHERE V3=? +---- + +==== Hint parameters +Hint parameters, if required, are placed within brackets after the hint name and are separated with commas. + +Hint parameter can be quoted. Quoted parameter is case sensitive. Quoted and unquoted parameters *cannot be* Review Comment: The hint parameter can be quoted. Quoted parameter is case-sensitive. The quoted and unquoted parameters cannot be defined for the same hint. -- 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]
