crepererum commented on code in PR #13706: URL: https://github.com/apache/datafusion/pull/13706#discussion_r1878372370
########## docs/source/user-guide/sql/dialect.md: ########## @@ -0,0 +1,53 @@ +<!--- + Licensed to the Apache Software Foundation (ASF) under one + or more contributor license agreements. See the NOTICE file + distributed with this work for additional information + regarding copyright ownership. The ASF licenses this file + to you under the Apache License, Version 2.0 (the + "License"); you may not use this file except in compliance + with the License. You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, + software distributed under the License is distributed on an + "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY + KIND, either express or implied. See the License for the + specific language governing permissions and limitations + under the License. +--> + +# SQL Dialect + +The included SQL supported in Apache DataFusion mostly follows the [PostgreSQL +SQL dialect], including: + +- The sql parser and [SQL planner] +- Type checking, analyzer, and type coercions +- Semantics of functions bundled with DataFusion + +Notable exceptions: + +- Array/List functions and semantics follow the [DuckDB SQL dialect]. +- DataFusion's type system is based on the [Apache Arrow type system], and the mapping to PostgrSQL types is not always 1:1. +- DataFusion has its own syntax (dialect) for certain operations (like [`CREATE EXTERNAL TABLE`]) + +As Apache DataFusion is designed to be fully customizable, systems built on +DataFusion can and do implement different SQL semantics. Using DataFusion's APs, +you can provide alternate function definitions, type rules, and/or SQL syntax +that matches other systems such as Apache Spark or MySQL or your own custom +semantics. + +[postgresql sql dialect]: https://www.postgresql.org/docs/current/sql.html +[sql planner]: https://docs.rs/datafusion/latest/datafusion/sql/planner/struct.SqlToRel.html +[duckdb sql dialect]: https://duckdb.org/docs/sql/functions/array +[apache arrow type system]: https://arrow.apache.org/docs/format/Columnar.html#data-types +[`create external table`]: ddl.md#create-external-table + +## Rationale + +SQL Engines have a choice to either use an existing SQL dialect or define their +own. Using an existing dialect may not fit perfectly as it is hard to match +semantics exactly (need bug-for-bug compatibility), and is likely not what all Review Comment: More reasons for using pogstgres specifically: it is - rather extensive, in contrast to e.g. sqlite - rather well aligned w/ the SQL standard (at least that's my personal impression, after having faced MySQL) -- 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: github-unsubscr...@datafusion.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org --------------------------------------------------------------------- To unsubscribe, e-mail: github-unsubscr...@datafusion.apache.org For additional commands, e-mail: github-h...@datafusion.apache.org
