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Support Union as a function #10206
Description
Is your feature request related to a problem or challenge?
We have recently issues show that it is time to support Union
#10161 #10139 ScalarValue::iter_to_array
#10180 comparison_coercion
I think the first step is able to create Union in slt file.
Describe the solution you'd like
Follow DuckDB Union or others well-known system.
https://duckdb.org/docs/sql/data_types/union.html
First step might be able to create table with union type
query error DataFusion error: Error during planning: Inconsistent data type across values list at row 1 column 0\. Was Int64 but found Utf8
create table t1 (u union(num interger, str varchar)) as values
(1),
('two');
Describe alternatives you've considered
No response
Additional context
- Built Union on top of Struct
- Impl with
ScalarUDFImpl
Activity
[-]Support `Union`[/-][+]Support `Union` Type[/+][-]Support `Union` Type[/-][+]Support `Union` as a function[/+]vaibhawvipul commentedon Apr 24, 2024
I would like to work on this.
samuelcolvin commentedon Apr 24, 2024
As I mentioned here #7845 (comment), the most useful thing for me would be less ugly errors when you do try to compare a union with something else.
Also it would be good to be able to force people to cast unions in my case, so it would be nice if we could switch off
comparison_coercionsomehow.@vaibhawvipul if you're working on this, you might be interested in my logic in
datafusion-contrib/datafusion-functions-json/src/common_union.rsvaibhawvipul commentedon Apr 25, 2024
This was helpful @samuelcolvin. Thank you.
My approach is similar -
union_extract.vaibhawvipul commentedon May 16, 2024
take
gstvg commentedon Jun 25, 2024
I opened a PR that adds support for Union datatype on sqlparser which I hope can help here. If so, some review would be very appreciated, since sqlparser-rs dev-bandwith is a bit limited. Thanks 🙏
alamb commentedon Jan 13, 2026
I think we now have reasonable
UnionArraysupport -- see https://github.com/apache/datafusion/blob/main/datafusion/sqllogictest/test_files/union.sltalamb commentedon Jan 13, 2026
Let's open follow on tickets with any specific features we want to support