Re: [PR] [FLINK-34372][table-api] Support DESCRIBE CATALOG [flink]

["LadyForest (via GitHub)" <gi...@apache.org>]

LadyForest commented on code in PR #24275:
URL: https://github.com/apache/flink/pull/24275#discussion_r1510519137


##########
flink-table/flink-table-common/src/main/java/org/apache/flink/table/catalog/Catalog.java:
##########
@@ -781,4 +781,13 @@ void alterPartitionColumnStatistics(
             CatalogColumnStatistics columnStatistics,
             boolean ignoreIfNotExists)
             throws PartitionNotExistException, CatalogException;
+
+    /**
+     * Get a user defined catalog description.
+     *
+     * @return a user-implement catalog detailed explanation
+     */
+    default String explainCatalog() {

Review Comment:
   Nit: I know that even though the `explainCatalog` method was proposed by FLIP, I still want to point out that the Catalog itself is the subject that performs the explain action, so there's no need to overemphasize with `explainCatalog`. Simply using `explain` is enough. If we consider other interfaces, like `Table`, it's just use `explain`, not `explainTable`.



##########
flink-table/flink-table-common/src/main/java/org/apache/flink/table/catalog/AbstractCatalog.java:
##########
@@ -47,4 +51,31 @@ public String getName() {
     public String getDefaultDatabase() {
         return defaultDatabase;
     }
+
+    @Override
+    public String explainCatalog() {
+        StringBuilder sb = new StringBuilder();
+        Map<String, String> extraExplainInfo = extraExplainInfo();
+        sb.append("default database: ").append(defaultDatabase);
+        if (!extraExplainInfo.isEmpty()) {
+            sb.append("\n");
+            sb.append(
+                    extraExplainInfo.entrySet().stream()
+                            .map(entry -> entry.getKey() + ": " + entry.getValue())
+                            .collect(Collectors.joining("\n")));
+        }
+
+        // put the class name at the end
+        sb.append("\n").append(Catalog.super.explainCatalog());
+        return sb.toString();
+    }
+
+    /**
+     * Extra explain information used to print by DESCRIBE CATALOG catalogName statement.
+     *
+     * <p>Note: The class name and default database name of this catalog are no need to be added.
+     */
+    protected Map<String, String> extraExplainInfo() {
+        return new HashMap<>();

Review Comment:
   Nit: `return Collections.emptyMap<>();`



##########
flink-table/flink-table-api-java/src/main/java/org/apache/flink/table/operations/DescribeOperator.java:
##########
@@ -0,0 +1,29 @@
+/*
+ * 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.operations;
+
+import org.apache.flink.annotation.Internal;
+
+/**
+ * An {@link Operation} that describes the catalog, database and table, e.g. DESCRIBE CATALOG
+ * catalogName, DESCRIBE DATABASE [catalogName.]dataBaseName and DESCRIBE TABLE [[catalogName.]
+ * dataBaseName.]tableName.
+ */
+@Internal
+public interface DescribeOperator extends Operation, ExecutableOperation {}

Review Comment:
   Nit: I think the naming `DescribeOperator` needs to be reconsidered. All the rest Operations are named with `XXOperation`.



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