Github user gatorsmile commented on a diff in the pull request:
https://github.com/apache/spark/pull/14116#discussion_r71102142
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/systemcatalog/InformationSchema.scala
---
@@ -0,0 +1,312 @@
+/*
+ * 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.systemcatalog
+
+import scala.collection.mutable.ArrayBuffer
+
+import org.apache.spark.rdd.RDD
+import org.apache.spark.sql._
+import
org.apache.spark.sql.catalyst.catalog.SessionCatalog.{DEFAULT_DATABASE,
INFORMATION_SCHEMA_DATABASE}
+import org.apache.spark.sql.catalyst.dsl.plans._
+import org.apache.spark.sql.catalyst.expressions._
+import org.apache.spark.sql.catalyst.plans.logical.Project
+import org.apache.spark.sql.execution.datasources._
+import org.apache.spark.sql.internal.CatalogImpl
+import org.apache.spark.sql.sources._
+import org.apache.spark.sql.types._
+
+/**
+ * INFORMATION_SCHEMA is a database consisting views which provide
information about all of the
+ * tables, views, columns in a database.
+ *
+ * These views are designed to be populated by this package in order to be
independent from
+ * Spark catalog. To keep minimal dependency, currently INFORMATION_SCHEMA
views are implemented as
+ * Spark temporary views with a database prefix:
`SessionCatalog.INFORMATION_SCHEMA_DATABASE`.
+ *
+ * The following is the class hierarchy in this package rooted at
InformationSchemaRelationProvider.
+ *
+ * InformationSchemaRelationProvider
+ * -> DatabasesRelationProvider
+ * -> TablesRelationProvider
+ * -> ViewsRelationProvider
+ * -> ColumnsRelationProvider
+ * -> SessionVariablesRelationProvider
+ */
+
+/**
+ * InformationSchema object provides bootstrap and utility functions.
+ */
+object InformationSchema {
+
+ /**
+ * Register INFORMATION_SCHEMA database. SessionCatalog.catalog invokes
this function.
+ */
+ def registerInformationSchema(sparkSession: SparkSession): Unit = {
+ sparkSession.sql(s"CREATE DATABASE IF NOT EXISTS
$INFORMATION_SCHEMA_DATABASE")
--- End diff --
I am lost. A database `INFORMATION_SCHEMA_DATABASE` is created through a
SQL command, but the function `databaseExists` always returns true for the
database for `INFORMATION_SCHEMA_DATABASE`.
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