andygrove commented on code in PR #3132: URL: https://github.com/apache/arrow-datafusion/pull/3132#discussion_r946055632
########## docs/source/user-guide/sql/subqueries.md: ########## @@ -0,0 +1,98 @@ +<!--- + 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. +--> + +# Subqueries + +DataFusion supports `EXISTS`, `IN`, and Scalar Subqueries. + +The examples below are based on the following table. + +```sql +❯ select * from x; ++----------+----------+ +| column_1 | column_2 | ++----------+----------+ +| 1 | 2 | ++----------+----------+ +``` + +## EXISTS + +The `EXISTS` syntax can be used to find all rows in a relation where a correlated subquery produces one or more matches +for that row. Only correlated subqueries are supported. + +```sql +❯ select * from x y where exists (select * from x where x.column_1 = y.column_1); ++----------+----------+ +| column_1 | column_2 | ++----------+----------+ +| 1 | 2 | ++----------+----------+ +1 row in set. +``` + +## NOT EXISTS + +The `NOT EXISTS` syntax can be used to find all rows in a relation where a correlated subquery produces zero matches +for that row. Only correlated subqueries are supported. + +```sql +❯ select * from x y where not exists (select * from x where x.column_1 = y.column_1); +0 rows in set. +``` + +## IN + +The `IN` syntax can be used to find all rows in a relation where a given expression's value can be found in the +results of a correlated subquery. Only correlated subqueries are supported. Review Comment: Ha. I am learning more about DataFusion! Documentation is good! -- 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]
