[GitHub] [spark] imback82 commented on a change in pull request #25601: [SPARK-28856][SQL] Implement SHOW DATABASES for Data Source V2 Tables

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imback82 commented on a change in pull request #25601: [SPARK-28856][SQL] Implement SHOW DATABASES for Data Source V2 Tables
URL: https://github.com/apache/spark/pull/25601#discussion_r319711930
 
 

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 File path: sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/v2/ShowDatabasesExec.scala
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+/*
+ * 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.spark.sql.execution.datasources.v2
+
+import scala.collection.mutable.ArrayBuffer
+
+import org.apache.spark.rdd.RDD
+import org.apache.spark.sql.catalog.v2.CatalogV2Implicits.NamespaceHelper
+import org.apache.spark.sql.catalog.v2.SupportsNamespaces
+import org.apache.spark.sql.catalyst.InternalRow
+import org.apache.spark.sql.catalyst.encoders.RowEncoder
+import org.apache.spark.sql.catalyst.expressions.{Attribute, GenericRowWithSchema}
+import org.apache.spark.sql.catalyst.util.StringUtils
+import org.apache.spark.sql.execution.LeafExecNode
+
+/**
+ * Physical plan node for showing databases.
+ */
+case class ShowDatabasesExec(
+    output: Seq[Attribute],
+    catalog: SupportsNamespaces,
+    pattern: Option[String])
+    extends LeafExecNode {
+  override protected def doExecute(): RDD[InternalRow] = {
+    val namespaces = catalog.listNamespaces().flatMap(getNamespaces(catalog, _))
 
 Review comment:
   > Another option is to ignore the current namespace entirely. `SHOW NAMESPACES` would list the root, and `SHOW NAMESPACES IN ns1` lists namespaces in `ns1`. The context is always explicit.
   
   I like this idea. @cloud-fan are you OK with this approach?
   

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