dengziming commented on code in PR #51686:
URL: https://github.com/apache/spark/pull/51686#discussion_r2239419467
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sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/v2/V2ScanRelationPushDown.scala:
##########
@@ -226,10 +195,50 @@ object V2ScanRelationPushDown extends Rule[LogicalPlan]
with PredicateHelper {
}
}
- def generateJoinOutputAlias(name: String): String =
- s"${name}_${java.util.UUID.randomUUID().toString.replace("-", "_")}"
+ private def generateColumnAliasesForDuplicatedName(
+ leftSideRequiredColumnNames: Array[String],
+ rightSideRequiredColumnNames: Array[String]
+ ): (Array[SupportsPushDownJoin.ColumnWithAlias],
+ Array[SupportsPushDownJoin.ColumnWithAlias]) = {
+ // Count occurrences of each column name across both sides to identify
duplicates.
+ val allRequiredColumnNames = leftSideRequiredColumnNames ++
rightSideRequiredColumnNames
+ val allNameCounts: Map[String, Int] =
+ allRequiredColumnNames.groupBy(identity).view.mapValues(_.size).toMap
+ // Use Set for O(1) lookups when checking existing column names, claim all
names
+ // that appears only once to ensure they have highest priority.
+ val allClaimedAliases = mutable.HashSet.empty ++ allNameCounts.filter(_._2
== 1).keySet
+
+ // Track the next suffix index for each column name (starts at 0) to avoid
extreme worst
+ // case of O(n^2) alias generation.
+ val aliasSuffixIndex = mutable.HashMap[String, Int]().withDefaultValue(0)
+
+ def processColumn(name: String): SupportsPushDownJoin.ColumnWithAlias = {
+ // Ensure a name that appears only once does not require an alias.
+ if (allNameCounts(name) == 1) {
+ new SupportsPushDownJoin.ColumnWithAlias(name, null)
+ } else {
+ var attempt = aliasSuffixIndex(name)
+
+ // Generate candidate alias: use original name for the first attempt,
then append
+ // suffix for more attempts.
+ var candidate = if (attempt == 0) name else s"${name}_$attempt"
Review Comment:
I did this so we can try to keep more names unchanged, if we have `col, col,
col`, then the result can be `col, col_1, col_2`, and the first col doesn't
need an alias. I made a small improvement in the latest commit, PTAL.
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