chenhao-db opened a new pull request, #45934:
URL: https://github.com/apache/spark/pull/45934
### What changes were proposed in this pull request?
This PR adds a new `schema_of_variant_agg` expression. It returns the merged
schema in the SQL format of a variant column. Compared to `schema_of_variant`,
which is a scalar expression and returns one schema for one row, the
`schema_of_variant_agg` expression merges the schema of all rows.
Usage examples:
```
> SELECT schema_of_variant_agg(parse_json(j)) FROM VALUES ('1'), ('2'),
('3') AS tab(j);
BIGINT
> SELECT schema_of_variant_agg(parse_json(j)) FROM VALUES ('{"a": 1}'),
('{"b": true}'), ('{"c": 1.23}') AS tab(j);
STRUCT<a: BIGINT, b: BOOLEAN, c: DECIMAL(3,2)>
```
### Why are the changes needed?
This expression can help the user explore the content of variant values.
### Does this PR introduce _any_ user-facing change?
Yes. A new SQL expression is added.
### How was this patch tested?
Unit tests.
### Was this patch authored or co-authored using generative AI tooling?
No.
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