Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/17185#discussion_r207702684
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/package.scala
---
@@ -169,25 +181,50 @@ package object expressions {
})
}
- // Find matches for the given name assuming that the 1st part is a
qualifier (i.e. table name,
- // alias, or subquery alias) and the 2nd part is the actual name.
This returns a tuple of
+ // Find matches for the given name assuming that the 1st two parts
are qualifier
+ // (i.e. database name and table name) and the 3rd part is the
actual column name.
+ //
+ // For example, consider an example where "db1" is the database
name, "a" is the table name
+ // and "b" is the column name and "c" is the struct field name.
+ // If the name parts is db1.a.b.c, then Attribute will match
--- End diff --
we may need to check the SQL standard about how to resolve the ambiguity.
For `a.b.c`, it's possible that `a` is db name, `b` is table name, `c` is
column name. If there is no column named `c`, we should fail. It's also
possible that `a` is table name, `b` is column name, `c` is nested field name,
and it exists. What's the expected behavior here?
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