[SPARK-17642][SQL][FOLLOWUP] drop test tables and improve comments

## What changes were proposed in this pull request?

Drop test tables and improve comments.

## How was this patch tested?

Modified existing test.

Author: Zhenhua Wang <[email protected]>

Closes apache#19213 from wzhfy/useless_comment.

Author: wzhfy

sql/core/src/main/scala/org/apache/spark/sql/execution/command/tables.scala

@@ -632,8 +632,7 @@ case class DescribeTableCommand(
 }
 
 /**
- * A command to list the info for a column, including name, data type, column stats and comment.
- * This function creates a [[DescribeColumnCommand]] logical plan.
+ * A command to list the info for a column, including name, data type, comment and column stats.
  *
  * The syntax of using this command in SQL is:
  * {{{
@@ -809,8 +808,7 @@ case class ShowTablePropertiesCommand(table: TableIdentifier, propertyKey: Optio
 }
 
 /**
- * A command to list the column names for a table. This function creates a
- * [[ShowColumnsCommand]] logical plan.
+ * A command to list the column names for a table.
  *
  * The syntax of using this command in SQL is:
  * {{{
@@ -849,8 +847,6 @@ case class ShowColumnsCommand(
  * 1. If the command is called for a non partitioned table.
  * 2. If the partition spec refers to the columns that are not defined as partitioning columns.
  *
- * This function creates a [[ShowPartitionsCommand]] logical plan
- *
  * The syntax of using this command in SQL is:
  * {{{
  *   SHOW PARTITIONS [db_name.]table_name [PARTITION(partition_spec)]

sql/core/src/test/resources/sql-tests/inputs/describe-table-column.sql

@@ -1,17 +1,17 @@
 -- Test temp table
-CREATE TEMPORARY VIEW desc_col_temp_table (key int COMMENT 'column_comment') USING PARQUET;
+CREATE TEMPORARY VIEW desc_col_temp_view (key int COMMENT 'column_comment') USING PARQUET;
 
-DESC desc_col_temp_table key;
+DESC desc_col_temp_view key;
 
-DESC EXTENDED desc_col_temp_table key;
+DESC EXTENDED desc_col_temp_view key;
 
-DESC FORMATTED desc_col_temp_table key;
+DESC FORMATTED desc_col_temp_view key;
 
 -- Describe a column with qualified name
-DESC FORMATTED desc_col_temp_table desc_col_temp_table.key;
+DESC FORMATTED desc_col_temp_view desc_col_temp_view.key;
 
 -- Describe a non-existent column
-DESC desc_col_temp_table key1;
+DESC desc_col_temp_view key1;
 
 -- Test persistent table
 CREATE TABLE desc_col_table (key int COMMENT 'column_comment') USING PARQUET;
@@ -25,11 +25,17 @@ DESC EXTENDED desc_col_table key;
 DESC FORMATTED desc_col_table key;
 
 -- Test complex columns
-CREATE TABLE desc_col_complex_table (`a.b` int, col struct<x:int, y:string>) USING PARQUET;
+CREATE TABLE desc_complex_col_table (`a.b` int, col struct<x:int, y:string>) USING PARQUET;
 
-DESC FORMATTED desc_col_complex_table `a.b`;
+DESC FORMATTED desc_complex_col_table `a.b`;
 
-DESC FORMATTED desc_col_complex_table col;
+DESC FORMATTED desc_complex_col_table col;
 
 -- Describe a nested column
-DESC FORMATTED desc_col_complex_table col.x;
+DESC FORMATTED desc_complex_col_table col.x;
+
+DROP VIEW desc_col_temp_view;
+
+DROP TABLE desc_col_table;
+
+DROP TABLE desc_complex_col_table;

sql/core/src/test/resources/sql-tests/results/describe-table-column.sql.out

@@ -1,17 +1,17 @@
 -- Automatically generated by SQLQueryTestSuite
--- Number of queries: 15
+-- Number of queries: 18
 
 
 -- !query 0
-CREATE TEMPORARY VIEW desc_col_temp_table (key int COMMENT 'column_comment') USING PARQUET
+CREATE TEMPORARY VIEW desc_col_temp_view (key int COMMENT 'column_comment') USING PARQUET
 -- !query 0 schema
 struct<>
 -- !query 0 output
 
 
 
 -- !query 1
-DESC desc_col_temp_table key
+DESC desc_col_temp_view key
 -- !query 1 schema
 struct<info_name:string,info_value:string>
 -- !query 1 output
@@ -21,7 +21,7 @@ comment	column_comment
 
 
 -- !query 2
-DESC EXTENDED desc_col_temp_table key
+DESC EXTENDED desc_col_temp_view key
 -- !query 2 schema
 struct<info_name:string,info_value:string>
 -- !query 2 output
@@ -37,7 +37,7 @@ max_col_len	NULL
 
 
 -- !query 3
-DESC FORMATTED desc_col_temp_table key
+DESC FORMATTED desc_col_temp_view key
 -- !query 3 schema
 struct<info_name:string,info_value:string>
 -- !query 3 output
@@ -53,7 +53,7 @@ max_col_len	NULL
 
 
 -- !query 4
-DESC FORMATTED desc_col_temp_table desc_col_temp_table.key
+DESC FORMATTED desc_col_temp_view desc_col_temp_view.key
 -- !query 4 schema
 struct<info_name:string,info_value:string>
 -- !query 4 output
@@ -69,7 +69,7 @@ max_col_len	NULL
 
 
 -- !query 5
-DESC desc_col_temp_table key1
+DESC desc_col_temp_view key1
 -- !query 5 schema
 struct<>
 -- !query 5 output
@@ -136,15 +136,15 @@ max_col_len	4
 
 
 -- !query 11
-CREATE TABLE desc_col_complex_table (`a.b` int, col struct<x:int, y:string>) USING PARQUET
+CREATE TABLE desc_complex_col_table (`a.b` int, col struct<x:int, y:string>) USING PARQUET
 -- !query 11 schema
 struct<>
 -- !query 11 output
 
 
 
 -- !query 12
-DESC FORMATTED desc_col_complex_table `a.b`
+DESC FORMATTED desc_complex_col_table `a.b`
 -- !query 12 schema
 struct<info_name:string,info_value:string>
 -- !query 12 output
@@ -160,7 +160,7 @@ max_col_len	NULL
 
 
 -- !query 13
-DESC FORMATTED desc_col_complex_table col
+DESC FORMATTED desc_complex_col_table col
 -- !query 13 schema
 struct<info_name:string,info_value:string>
 -- !query 13 output
@@ -176,9 +176,33 @@ max_col_len	NULL
 
 
 -- !query 14
-DESC FORMATTED desc_col_complex_table col.x
+DESC FORMATTED desc_complex_col_table col.x
 -- !query 14 schema
 struct<>
 -- !query 14 output
 org.apache.spark.sql.AnalysisException
 DESC TABLE COLUMN command does not support nested data types: col.x;
+
+
+-- !query 15
+DROP VIEW desc_col_temp_view
+-- !query 15 schema
+struct<>
+-- !query 15 output
+
+
+
+-- !query 16
+DROP TABLE desc_col_table
+-- !query 16 schema
+struct<>
+-- !query 16 output
+
+
+
+-- !query 17
+DROP TABLE desc_complex_col_table
+-- !query 17 schema
+struct<>
+-- !query 17 output
+