cloud-fan commented on a change in pull request #25107: [SPARK-28344][SQL]
detect ambiguous self-join and fail the query
URL: https://github.com/apache/spark/pull/25107#discussion_r309639009
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File path: sql/core/src/main/scala/org/apache/spark/sql/Column.scala
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@@ -144,11 +153,16 @@ class Column(val expr: Expression) extends Logging {
override def toString: String = toPrettySQL(expr)
override def equals(that: Any): Boolean = that match {
- case that: Column => that.expr.equals(this.expr)
+ case that: Column => that.normalizedExpr().equals(this.normalizedExpr())
case _ => false
}
- override def hashCode: Int = this.expr.hashCode()
+ override def hashCode: Int = this.normalizedExpr().hashCode()
+
+ private def normalizedExpr(): Expression = expr match {
Review comment:
good catch!
However, I'm not able to test it. The `normalizedExpr` is only used in
`equals` and `hashCode`. For `df("a.b")`, we will create a new alias everytime,
see `AttributeSeq.resolve`.
That said, if we get multiple `Column` instances via calling `df("a.b")`
multiple times, these `Column` instances will never equal to each other,
because the alias is different.
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