xuefuz commented on a change in pull request #8404: [FLINK-11476][table] Create 
CatalogManager to manage multiple catalogs
URL: https://github.com/apache/flink/pull/8404#discussion_r282981545
 
 

 ##########
 File path: 
flink-table/flink-table-planner/src/main/java/org/apache/flink/table/catalog/CatalogCalciteSchema.java
 ##########
 @@ -0,0 +1,122 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.table.catalog;
+
+import org.apache.flink.annotation.Internal;
+import org.apache.flink.table.catalog.exceptions.CatalogException;
+import org.apache.flink.table.catalog.exceptions.DatabaseNotExistException;
+
+import org.apache.calcite.linq4j.tree.Expression;
+import org.apache.calcite.rel.type.RelProtoDataType;
+import org.apache.calcite.schema.Function;
+import org.apache.calcite.schema.Schema;
+import org.apache.calcite.schema.SchemaPlus;
+import org.apache.calcite.schema.SchemaVersion;
+import org.apache.calcite.schema.Schemas;
+import org.apache.calcite.schema.Table;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.Collection;
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ * A mapping between Flink's catalog and Calcite's schema. This enables to 
look up and access tables
+ * in SQL queries without registering tables in advance. Databases are 
registered as sub-schemas in the schema.
+ */
+@Internal
+public class CatalogCalciteSchema implements Schema {
+       private static final Logger LOGGER = 
LoggerFactory.getLogger(CatalogCalciteSchema.class);
+
+       private final String catalogName;
+       private final Catalog catalog;
+
+       public CatalogCalciteSchema(String catalogName, Catalog catalog) {
+               this.catalogName = catalogName;
+               this.catalog = catalog;
+       }
+
+       /**
+        * Look up a sub-schema (database) by the given sub-schema name.
+        *
+        * @param schemaName name of sub-schema to look up
+        * @return the sub-schema with a given dbName, or null
+        */
+       @Override
+       public Schema getSubSchema(String schemaName) {
+
+               if (catalog.databaseExists(schemaName)) {
+                       return new DatabaseCalciteSchema(schemaName, catalog);
+               } else {
+                       LOGGER.error(String.format("Schema %s does not exist in 
catalog %s", schemaName, catalogName));
+                       throw new CatalogException(new 
DatabaseNotExistException(catalogName, schemaName));
+               }
+       }
+
+       @Override
+       public Set<String> getSubSchemaNames() {
+               return new HashSet<>(catalog.listDatabases());
+       }
+
+       @Override
+       public Table getTable(String name) {
+               return null;
+       }
+
+       @Override
+       public Set<String> getTableNames() {
+               return new HashSet<>();
+       }
+
+       @Override
+       public RelProtoDataType getType(String name) {
+               return null;
 
 Review comment:
   Returning "null" means no type with the given name is found. I'm not sure if 
that's desired, but feel free to add an TODO item for this if necessary.

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