YiwenWu commented on code in PR #3797:
URL: https://github.com/apache/calcite/pull/3797#discussion_r1615584653
##########
core/src/main/java/org/apache/calcite/sql/util/SqlShuttle.java:
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@@ -135,6 +136,14 @@ public CallCopyingArgHandler(SqlCall call, boolean
alwaysCopy) {
if (newOperand != operand) {
update = true;
}
+
+ // Prevent nesting AS calls
+ if (i == 0 && expr instanceof SqlCall
Review Comment:
To avoid redundant `if` judgments, I suggest that the solution be more
targeted at the source `SqlValidatorImpl#expandExprFromJoin`.
For example:
```
boolean hasAlias = can judge the result from `sqlSelect` and `selectItem`
private static SqlNode expandExprFromJoin(SqlJoin join,
SqlIdentifier identifier, boolean hasAlias, SelectScope scope) {
....
SqlCall coalesce =
SqlStdOperatorTable.COALESCE.createCall(SqlParserPos.ZERO,
qualifiedNode.get(0),
qualifiedNode.get(1));
return hasAlias ? coalesce :
SqlStdOperatorTable.AS.createCall(SqlParserPos.ZERO,
coalesce, new SqlIdentifier(name, SqlParserPos.ZERO));
....
}
```
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