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docs: Added Special Functions Page (#13102)
* Added special function page * Add index entry, tweak wording * Improve example * Update docs/source/user-guide/sql/special_functions.md --------- Co-authored-by: Andrew Lamb <[email protected]> Co-authored-by: Oleks V <[email protected]>
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‎docs/source/user-guide/sql/index.rst‎

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window_functions_new
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scalar_functions
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scalar_functions_new
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special_functions
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sql_status
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write_options

‎docs/source/user-guide/sql/scalar_functions.md‎

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## Array Functions
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- [unnest](#unnest)
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- [range](#range)
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### `unnest`
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Transforms an array into rows.
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#### Arguments
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- **array**: Array expression to unnest.
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Can be a constant, column, or function, and any combination of array operators.
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#### Examples
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```
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> select unnest(make_array(1, 2, 3, 4, 5));
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+------------------------------------------------------------------+
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| unnest(make_array(Int64(1),Int64(2),Int64(3),Int64(4),Int64(5))) |
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+------------------------------------------------------------------+
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| 1 |
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| 5 |
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+------------------------------------------------------------------+
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```
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```
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> select unnest(range(0, 10));
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+-----------------------------------+
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| unnest(range(Int64(0),Int64(10))) |
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+-----------------------------------+
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| 0 |
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| 1 |
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+-----------------------------------+
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```
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### `range`
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Returns an Arrow array between start and stop with step. `SELECT range(2, 10, 3) -> [2, 5, 8]` or
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- generate_series
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## Struct Functions
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- [unnest](#unnest-struct)
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For more struct functions see the new documentation [
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`here`](https://datafusion.apache.org/user-guide/sql/scalar_functions_new.html)
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### `unnest (struct)`
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Unwraps struct fields into columns.
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#### Arguments
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- **struct**: Object expression to unnest.
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Can be a constant, column, or function, and any combination of object operators.
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#### Examples
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```
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> select * from foo;
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+---------------------+
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| column1 |
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+---------------------+
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| {a: 5, b: a string} |
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+---------------------+
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> select unnest(column1) from foo;
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+-----------------------+-----------------------+
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| unnest(foo.column1).a | unnest(foo.column1).b |
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+-----------------------+-----------------------+
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| 5 | a string |
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+-----------------------+-----------------------+
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```
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## Other Functions
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See the new documentation [`here`](https://datafusion.apache.org/user-guide/sql/scalar_functions_new.html)

‎docs/source/user-guide/sql/special_functions.md‎

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<!---
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Licensed to the Apache Software Foundation (ASF) under one
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or more contributor license agreements. See the NOTICE file
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distributed with this work for additional information
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regarding copyright ownership. The ASF licenses this file
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to you under the Apache License, Version 2.0 (the
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"License"); you may not use this file except in compliance
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with the License. You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing,
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software distributed under the License is distributed on an
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"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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KIND, either express or implied. See the License for the
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specific language governing permissions and limitations
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under the License.
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-->
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# Special Functions
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## Expansion Functions
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- [unnest](#unnest)
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- [unnest(struct)](#unnest-struct)
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### `unnest`
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Expands an array or map into rows.
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#### Arguments
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- **array**: Array expression to unnest.
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Can be a constant, column, or function, and any combination of array operators.
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#### Examples
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```sql
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> select unnest(make_array(1, 2, 3, 4, 5)) as unnested;
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+----------+
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| unnested |
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+----------+
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| 1 |
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| 2 |
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| 3 |
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| 4 |
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| 5 |
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+----------+
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```
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```sql
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> select unnest(range(0, 10)) as unnested_range;
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+----------------+
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| unnested_range |
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+----------------+
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| 0 |
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| 1 |
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| 4 |
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| 6 |
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| 7 |
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| 8 |
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| 9 |
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+----------------+
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```
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### `unnest (struct)`
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Expand a struct fields into individual columns.
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#### Arguments
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- **struct**: Object expression to unnest.
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Can be a constant, column, or function, and any combination of object operators.
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#### Examples
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```sql
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> create table foo as values ({a: 5, b: 'a string'}), ({a:6, b: 'another string'});
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> create view foov as select column1 as struct_column from foo;
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> select * from foov;
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+---------------------------+
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| struct_column |
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+---------------------------+
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| {a: 5, b: a string} |
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| {a: 6, b: another string} |
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+---------------------------+
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> select unnest(struct_column) from foov;
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+------------------------------------------+------------------------------------------+
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| unnest_placeholder(foov.struct_column).a | unnest_placeholder(foov.struct_column).b |
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+------------------------------------------+------------------------------------------+
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| 5 | a string |
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| 6 | another string |
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+------------------------------------------+------------------------------------------+
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```

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