zzwqqq commented on code in PR #5077:
URL: https://github.com/apache/calcite/pull/5077#discussion_r3556628632
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core/src/main/java/org/apache/calcite/rel/rel2sql/SqlImplementor.java:
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@@ -2444,18 +2499,89 @@ public Context qualifiedContext() {
return aliasContext(aliases, true);
}
+ /** Returns a result that uses derived-table field names. */
+ private Result forDerivedTable() {
+ if (neededType == null) {
+ return this;
+ }
+ // Internal derived table aliases may need dialect-specific uniqueness.
+ final List<String> fieldNames = derivedTableFieldNames(neededType);
+ if (fieldNames.equals(neededType.getFieldNames())) {
+ return this;
+ }
+ final RelDataType type = renameRowTypeFields(neededType, fieldNames);
+ final SqlNode newNode = withDerivedTableFieldNames(fieldNames);
+ final ImmutableMap.Builder<String, RelDataType> aliasBuilder =
+ ImmutableMap.builder();
+ for (Map.Entry<String, RelDataType> alias : aliases.entrySet()) {
+ aliasBuilder.put(alias.getKey(),
+ alias.getValue() == neededType ? type : alias.getValue());
+ }
+ return new Result(newNode, clauses, neededAlias, type,
aliasBuilder.build(), anon,
+ ignoreClauses, expectedClauses, expectedRel, forceExplicitAlias);
+ }
+
+ /** Rewrites a result for use in a derived table. */
+ private SqlNode withDerivedTableFieldNames(List<String> fieldNames) {
+ if (node.getKind() == SqlKind.AS) {
+ final SqlCall call = (SqlCall) node;
+ final List<SqlNode> operands = call.getOperandList();
+ final int fieldAliasStart = 2;
+ if (operands.size() == fieldNames.size() + fieldAliasStart) {
+ final List<SqlNode> newOperands = new ArrayList<>(operands.size());
+ newOperands.add(call.operand(0));
+ newOperands.add(call.operand(1));
+ for (String fieldName : fieldNames) {
+ newOperands.add(new SqlIdentifier(fieldName, POS));
+ }
+ return SqlStdOperatorTable.AS.createCall(POS, newOperands);
+ }
+ }
+ return withSelectFieldNames(fieldNames);
+ }
+
+ /** Rewrites a SELECT list to expose the given field names. */
Review Comment:
Thanks. I add clearer docs and assertion.
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