JackieTien97 commented on code in PR #17960:
URL: https://github.com/apache/iotdb/pull/17960#discussion_r3432746539
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iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/analyzer/StatementAnalyzer.java:
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@@ -1670,11 +2185,25 @@ private SelectAnalysis analyzeSelect(QuerySpecification
node, Scope scope) {
outputPosition++;
}
} else {
+ SelectAliasLookup visibleAliases = visibleAliasBuilder.build();
Review Comment:
Nit / follow-up suggestion: this builds a fresh immutable
`SelectAliasLookup` for every `SingleColumn`. Since the `SelectAliasLookup`
constructor copies the whole current alias map and each alias list, analyzing a
very wide SELECT list with many reusable aliases ends up doing repeated prefix
copies, i.e. roughly O(N^2) alias-map copying.
This is probably fine for normal SELECT lists, but it may be worth avoiding
the repeated snapshots by using an incremental/shared immutable lookup
structure, or by exposing a read-only lookup view over the builder whose
visible state grows left-to-right.
Could you also add IT/regression coverage for this area? In particular, it
would be useful to cover a wide SELECT-list LCA chain/reuse case, plus the edge
cases around delimited/quoted alias case sensitivity, named `WINDOW`
definitions not seeing SELECT aliases, `DISTINCT` with LCA and no `ORDER BY`,
and LCA references in window frame bounds.
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