james-willis commented on code in PR #24865:
URL: https://github.com/apache/datafusion/pull/24865#discussion_r4392419661
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datafusion/common/src/metadata.rs:
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@@ -117,6 +117,36 @@ pub fn check_metadata_with_storage_equal(
Ok(())
}
+/// Compute the field metadata to propagate for an expression whose result
+/// may come from any one of several inputs coerced to a common type, such as
+/// `COALESCE`, `NVL2`, or `CASE WHEN`.
+///
+/// Returns the first non-empty metadata among the fields whose data type is
+/// not `Null` (an untyped NULL literal carries no metadata and cannot
+/// contribute a typed value), or empty metadata if there is none.
Review Comment:
This is what I found up doing. I think enforcing the extension names match
at least is good.
I agree its probably hard to be more strict on the metadata. I am thinking
of CRSes in SedonaDB
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