[SPARK-15952][SQL] fix "show databases" ordering issue

## What changes were proposed in this pull request?

Two issues I've found for "show databases" command:

1. The returned database name list was not sorted, it only works when "like" was used together; (HIVE will always return a sorted list)

2. When it is used as sql("show databases").show, it will output a table with column named as "result", but for sql("show tables").show, it will output the column name as "tableName", so I think we should be consistent and use "databaseName" at least.

## How was this patch tested?

Updated existing test case to test its ordering as well.

Author: bomeng <bmeng@us.ibm.com>

Closes #13671 from bomeng/SPARK-15952.

3 files changed, 6 insertions, 6 deletions

diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/catalog/InMemoryCatalog.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/catalog/InMemoryCatalog.scala
index 60525794ed..14da30a36f 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/catalog/InMemoryCatalog.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/catalog/InMemoryCatalog.scala
@@ -178,7 +178,7 @@ class InMemoryCatalog(hadoopConfig: Configuration = new Configuration) extends E
   }
 
   override def listDatabases(): Seq[String] = synchronized {
-    catalog.keySet.toSeq
+    catalog.keySet.toSeq.sorted
   }
 
   override def listDatabases(pattern: String): Seq[String] = synchronized {
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/command/databases.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/command/databases.scala
index cefe0f6e62..597ec27ce6 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/command/databases.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/command/databases.scala
@@ -33,9 +33,9 @@ import org.apache.spark.sql.types.StringType
  */
 case class ShowDatabasesCommand(databasePattern: Option[String]) extends RunnableCommand {
 
-  // The result of SHOW DATABASES has one column called 'result'
+  // The result of SHOW DATABASES has one column called 'databaseName'
   override val output: Seq[Attribute] = {
-    AttributeReference("result", StringType, nullable = false)() :: Nil
+    AttributeReference("databaseName", StringType, nullable = false)() :: Nil
   }
 
   override def run(sparkSession: SparkSession): Seq[Row] = {
diff --git a/sql/core/src/test/scala/org/apache/spark/sql/execution/command/DDLSuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/execution/command/DDLSuite.scala
index a7e6893caa..e15fcf4326 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/execution/command/DDLSuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/execution/command/DDLSuite.scala
@@ -708,11 +708,11 @@ class DDLSuite extends QueryTest with SharedSQLContext with BeforeAndAfterEach {
   }
 
   test("show databases") {
-    sql("CREATE DATABASE showdb1A")
     sql("CREATE DATABASE showdb2B")
+    sql("CREATE DATABASE showdb1A")
 
-    assert(
-      sql("SHOW DATABASES").count() >= 2)
+    // check the result as well as its order
+    checkDataset(sql("SHOW DATABASES"), Row("default"), Row("showdb1a"), Row("showdb2b"))
 
     checkAnswer(
       sql("SHOW DATABASES LIKE '*db1A'"),