[CALCITE-7440] Avoid ambiguous rel2sql correlation fallback

Author: bvolpato

core/src/main/java/org/apache/calcite/rel/rel2sql/SqlImplementor.java

@@ -1589,10 +1589,7 @@ public static SqlNode toSql(RexLiteral literal) {
   protected Context getAliasContext(RexCorrelVariable variable) {
     Context context = correlTableMap.get(variable.id);
     if (context == null) {
-      // Some rewrites can introduce a new correlation id that still points to
-      // the same outer scope. Reuse a compatible known context before failing.
-      context = findCompatibleCorrelContext(variable.id, variable.getType().getFieldCount());
-      if (context == null && correlTableMap.isEmpty()) {
+      if (correlTableMap.isEmpty()) {
         context =
             aliasContext(ImmutableMap.of(variable.id.getName(), variable.getType()), true);
       }
@@ -1603,28 +1600,6 @@ protected Context getAliasContext(RexCorrelVariable variable) {
     return requireNonNull(context, () -> "variable " + variable.id + " is not found");
   }
 
-  private @Nullable Context findCompatibleCorrelContext(CorrelationId missingId,
-      int expectedFieldCount) {
-    Context fallback = null;
-    String fallbackName = null;
-    for (Map.Entry<CorrelationId, Context> entry : correlTableMap.entrySet()) {
-      final CorrelationId id = entry.getKey();
-      final Context context = entry.getValue();
-      if (id.equals(missingId)) {
-        continue;
-      }
-      if (context.fieldCount == expectedFieldCount) {
-        return context;
-      }
-      final String name = id.getName();
-      if (fallbackName == null || name.compareTo(fallbackName) < 0) {
-        fallbackName = name;
-        fallback = context;
-      }
-    }
-    return fallback;
-  }
-
   /** Simple implementation of {@link Context} that cannot handle sub-queries
    * or correlations. Because it is so simple, you do not need to create a
    * {@link SqlImplementor} or {@link org.apache.calcite.tools.RelBuilder}