92ae271081
### What changes were proposed in this pull request? Document SHOW COLUMNS statement in SQL Reference Guide. ### Why are the changes needed? Currently Spark lacks documentation on the supported SQL constructs causing confusion among users who sometimes have to look at the code to understand the usage. This is aimed at addressing this issue. ### Does this PR introduce any user-facing change? Yes. **Before:** There was no documentation for this. **After.** <img width="1234" alt="Screen Shot 2019-09-02 at 11 07 48 PM" src="https://user-images.githubusercontent.com/14225158/64148033-0fe77300-cdd7-11e9-93ee-e5951c7ed33c.png"> <img width="1234" alt="Screen Shot 2019-09-02 at 11 08 08 PM" src="https://user-images.githubusercontent.com/14225158/64148039-137afa00-cdd7-11e9-8bec-634ea9d2594c.png"> <img width="1234" alt="Screen Shot 2019-09-02 at 11 11 45 PM" src="https://user-images.githubusercontent.com/14225158/64148046-17a71780-cdd7-11e9-91c3-95a9c97e7a77.png"> ### How was this patch tested? Tested using jykyll build --serve Closes #25531 from dilipbiswal/ref-doc-show-columns. Lead-authored-by: Dilip Biswal <dbiswal@us.ibm.com> Co-authored-by: Xiao Li <gatorsmile@gmail.com> Signed-off-by: Xiao Li <gatorsmile@gmail.com>
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| layout | title | displayTitle | license |
|---|---|---|---|
| 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
{% highlight sql %} SHOW COLUMNS table [ database ] {% endhighlight %}
Parameters
table-
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: KeywordsINandFROMare interchangeable. database-
Specifies an optional database name. The table is resolved from this database when it
is specified. Please note that when this parameter is specified then table
name should not be qualified with a different database name.
Syntax:{ IN | FROM } database_name
Note: KeywordsINandFROMare interchangeable.
Examples
{% highlight sql %}
-- 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|
+---------+
{% endhighlight %}