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spark-instrumented-optimizer/docs/sql-ref-syntax-aux-show-columns.md
Xiao Li b5ecc41c73 [SPARK-28806][DOCS][FOLLOW-UP] Remove unneeded HTML from the MD file 
### What changes were proposed in this pull request?
This PR is to clean up the markdown file in SHOW COLUMNS page.

- remove the unneeded embedded inline HTML markup by using the basic markdown syntax.
- use the ``` sql for highlighting the SQL syntax.

### Why are the changes needed?
Make the doc cleaner and easily editable by MD editors.

### Does this PR introduce _any_ user-facing change?
NO

### How was this patch tested?
**Before**

![Screen Shot 2020-04-29 at 5 20 11 PM](https://user-images.githubusercontent.com/11567269/80661963-fa4d4a80-8a44-11ea-9dea-c43cda6de010.png)

**After**

![Screen Shot 2020-04-29 at 6 03 50 PM](https://user-images.githubusercontent.com/11567269/80661940-f15c7900-8a44-11ea-9943-a83e8d8618fb.png)

Closes #28414 from gatorsmile/cleanupShowColumns.

Lead-authored-by: Xiao Li <gatorsmile@gmail.com>
Co-authored-by: gatorsmile <gatorsmile@gmail.com>
Signed-off-by: gatorsmile <gatorsmile@gmail.com>
2020-04-30 09:34:56 -07:00

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global SHOW COLUMNS SHOW COLUMNS 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.

Description

Return the list of columns in a table. If the table does not exist, an exception is thrown.

Syntax

SHOW COLUMNS table_identifier [ database ]

Parameters

  • table_identifier

    Specifies the table name of an existing table. The table may be optionally qualified with a database name.

    Syntax: { IN | FROM } [ database_name . ] table_name

    Note: Keywords IN and FROM are interchangeable.

  • database

    Specifies an optional database name. The table is resolved from this database when it is specified. When this parameter is specified then table name should not be qualified with a different database name.

    Syntax: { IN | FROM } database_name

    Note: Keywords IN and FROM are interchangeable.

Examples

-- Create `customer` table in `salesdb` database;
USE salesdb;
CREATE TABLE customer(
    cust_cd INT,
    name VARCHAR(100),
    cust_addr STRING);

-- List the columns of `customer` table in current database.
SHOW COLUMNS IN customer;
  +---------+
  | col_name|
  +---------+
  |  cust_cd|
  |     name|
  |cust_addr|
  +---------+

-- List the columns of `customer` table in `salesdb` database.
SHOW COLUMNS IN salesdb.customer;
  +---------+
  | col_name|
  +---------+
  |  cust_cd|
  |     name|
  |cust_addr|
  +---------+

-- List the columns of `customer` table in `salesdb` database
SHOW COLUMNS IN customer IN salesdb;
  +---------+
  | col_name|
  +---------+
  |  cust_cd|
  |     name|
  |cust_addr|
  +---------+

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