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= Working with SQL

Ignite comes with ANSI-99 compliant, horizontally scalable and fault-tolerant distributed SQL database. The distribution is provided either by partitioning the data across cluster nodes or by full replication, depending on the use case.

As a SQL database, Ignite supports all DML commands including SELECT, UPDATE, INSERT, and DELETE queries and also implements a subset of DDL commands relevant for distributed systems.

You can interact with Ignite as you would with any other SQL enabled storage by connecting with link:SQL/JDBC/jdbc-driver/[JDBC] or link:SQL/ODBC/odbc-driver[ODBC] drivers from both external tools and applications. Java, .NET and C++ developers can leverage native  link:SQL/sql-api[SQL APIs].

Internally, SQL tables have the same data structure as link:data-modeling/data-modeling#key-value-cache-vs-sql-table[key-value caches]. It means that you can change partition distribution of your data and leverage link:data-modeling/affinity-collocation[affinity colocation techniques] for better performance.

Ignite's default SQL engine uses H2 Database to parse and optimize queries and generate execution plans, but also the Apache Calcite-based SQL engine can be enabled to execute queries. For more information about Apache Calcite-based SQL engine, see the link:SQL/sql-calcite[Calcite-based SQL engine, window=_blank] section.

== Distributed Queries

Queries against link:data-modeling/data-partitioning#partitioned[partitioned] tables are executed in a distributed manner:

- The query is parsed and split into multiple “map” queries and a single “reduce” query.
- All the map queries are executed on all the nodes where required data resides.
- All the nodes provide result sets of local execution to the query initiator that, in turn, will merge provided result sets into the final results.

You can force a query to be processed locally, i.e. on the subset of data that is stored on the node where the query is executed.

== Local Queries

If a query is executed over a link:data-modeling/data-partitioning#replicated[replicated] table, it will be run against the local data.

Queries over partitioned tables are executed in a distributed manner.
However, you can force local execution of a query over a partitioned table.
See link:SQL/sql-api#local-execution[Local Execution] for details.


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== Known Limitations
TODO

https://apacheignite-sql.readme.io/docs/how-ignite-sql-works#section-known-limitations

https://issues.apache.org/jira/browse/IGNITE-7822 - describe this if not fixed
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