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[SPARK-28810][DOC][SQL] Document SHOW TABLES in SQL Reference. #25561

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80 changes: 79 additions & 1 deletion docs/sql-ref-syntax-aux-show-tables.md
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Expand Up @@ -18,5 +18,83 @@ license: |
See the License for the specific language governing permissions and
limitations under the License.
---
### Description

**This page is under construction**
List all the `tables` from the database with `database-name` and `is temporary table`.

@dilipbiswal dilipbiswal Sep 22, 2019

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@shivusondur Sorry.. re-reading this one last time :-)
SHOW TABLES statement returns all the tables for an optionally specified database. Additionally, the output
of this statement may be filtered via an optional matching pattern. If no database is specified then the tables
are returned from the current database.

@shivusondur shivusondur Sep 23, 2019

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DOne


### Syntax
{% highlight sql %}
SHOW TABLES [{FROM|IN} database_name] [LIKE 'regex_pattern']
{% endhighlight %}

### Parameters
<dl>
<dt><code><em>{FROM|IN} database_name</em></code></dt>
<dd>
Specifies the `database` name from which tables are listed.
</dd>
<dt><code><em>LIKE 'regex_pattern'</em></code></dt>
<dd>
Specifies the regex pattern that is used to filter out unwanted tables.
<br> - Only `*` and `|` are allowed as wildcard pattern.

@dilipbiswal dilipbiswal Sep 21, 2019

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@shivusondur Can you please include the example with output using the 'I' as wildcard ? From the code its not clear to me if this is supported.

@shivusondur shivusondur Sep 22, 2019 •
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@dilipbiswal
Done

@srowen srowen Sep 28, 2019

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| isn't a wildcard pattern, so I wouldn't imply it is.
Is it really treated as a full regex otherwise? if not, I wouldn't call it a regex unless it is generally called this in other similar references.

@dilipbiswal dilipbiswal Sep 28, 2019

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@srowen Thats a very good point Sean. How about we name the pattern 'identifier_with_wildcards' (and describe as such) as mentioned in ShowTablesCommand's comment ?

@srowen srowen Sep 29, 2019

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Is it a SQL-like pattern that supports wildcards like %? then I'd just call it a pattern

@dilipbiswal dilipbiswal Sep 29, 2019

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@srowen I quickly tried in my env. It does not support SQL-like pattern like %. I only saw the following work :

  • * : Matches 0 or more characters.
  • . : Matches a char
  • | : works like or expression.

@shivusondur Can you please confirm ?

@shivusondur shivusondur Sep 30, 2019

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@dilipbiswal @srowen
I also tesed, it is same behaviour you mentioned above.
It will use the below method to handle, here they are handling "|" and "*" seperatly, remaining treating as regex

spark/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/StringUtils.scala

Line 88 in e1ea806

def filterPattern(names: Seq[String], pattern: String): Seq[String] = {

@srowen srowen Sep 30, 2019

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OK, your comment is consistent with the docs then. Hm, but isn't it more accurate to say that * and | don't work like in regexes? * matches 0 or more characters, and | delimits whole regexes, which is different, but the rest is the same. Maybe a comment more like that. "The pattern is a regex except that * matches 0 or more characters by itself, and | may only be used at the top level to delimit alternative regexes to match." ?

@shivusondur shivusondur Oct 1, 2019

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@srowen @dilipbiswal
Thank you both for your time in reviewing.

I updated according to your suggestion and screenshot also I updated.
Now it will look like below.
image

<br> - Excluding `*` and `|` the remaining pattern follows the regex semantics.
<br> - The leading and trailing blanks are trimmed in the input pattern before processing.
</dd>
</dl>

### Example
{% highlight sql %}
-- List all tables in default database
SHOW TABLES;
+-----------+------------+--------------+--+

@dilipbiswal dilipbiswal Sep 21, 2019 •
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Please lets fix the formatting. Did we construct this output by hand ? Can we paste the
actual output here please so we preserve the formatting.

@shivusondur shivusondur Sep 22, 2019

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@dilipbiswal
I just Copy and paste the actual output from the Beeline console
Here is the beeline console snap
image

In the UI it looks like below, i think it is normal
image

Only in the git file editor, it shows inconsistent.

| database | tableName | isTemporary |
+-----------+------------+--------------+--+
| default | sam | false |
| default | sam1 | false |
| default | suj | false |
+-----------+------------+--------------+--+

-- List all tables from userdb database
SHOW TABLES FROM userdb;
+-----------+------------+--------------+--+
| database | tableName | isTemporary |
+-----------+------------+--------------+--+
| userdb | user1 | false |
| userdb | user2 | false |
+-----------+------------+--------------+--+

-- List all tables in userdb database
SHOW TABLES IN userdb;
+-----------+------------+--------------+--+
| database | tableName | isTemporary |
+-----------+------------+--------------+--+
| userdb | user1 | false |
| userdb | user2 | false |
+-----------+------------+--------------+--+

-- List all tables from default database matching the pattern `sam*`
SHOW TABLES FROM default LIKE 'sam*';
+-----------+------------+--------------+--+
| database | tableName | isTemporary |
+-----------+------------+--------------+--+
| default | sam | false |
| default | sam1 | false |
+-----------+------------+--------------+--+

-- List all tables matching the pattern `sam*|suj`

@dilipbiswal dilipbiswal Sep 22, 2019

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Nit: can we have a line between previous test and this one.

@shivusondur shivusondur Sep 22, 2019

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@dilipbiswal
Done, updated the snap's also.

SHOW TABLES LIKE 'sam*|suj';
+-----------+------------+--------------+--+
| database | tableName | isTemporary |
+-----------+------------+--------------+--+
| default | sam | false |
| default | sam1 | false |
| default | suj | false |
+-----------+------------+--------------+--+

{% endhighlight %}
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### Related statements
- [CREATE TABLE](sql-ref-syntax-ddl-create-table.html)
- [DROP TABLE](sql-ref-syntax-ddl-drop-table.html)
- [CREATE DATABASE](sql-ref-syntax-ddl-create-database.html)
- [DROP DATABASE](sql-ref-syntax-ddl-drop-database.html)