In this blog post, I will look at a few handy uses of the SELECT and SHOW commands to retrieve information in MySQL. SHOW returns useful information on databases, tables, etc…
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Note: All data, names or naming found within the database presented in this post, are strictly used for practice, learning, instruction, and testing purposes. It by no means depicts actual data belonging to or being used by any party or organization.
OS and DB used:
- Xubuntu Linux 16.04.5 LTS (Xenial Xerus)
- MySQL 5.7.23
What database am I currently in?
1 2 3 4 5 6 7 | mysql> SELECT DATABASE(); +------------+ | DATABASE() | +------------+ | asbuilt | +------------+ 1 row in set (0.00 sec) |
What tables, if any, are present in the current database?
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 | mysql> SHOW TABLES; +----------------------+ | Tables_in_asbuilt | +----------------------+ | asset_staging | | category | | closer_look | | coating_details | | degree_value | | diameter | | find_degree | | flagged_asset | | grade | | manufacturer | | pipe | | pipe_category | | pipe_coating_details | | pipe_grade | | pipe_manufacturer | | pw_wall_thickness | | wall_thickness | +----------------------+ 17 rows in set (0.01 sec) |
I am curious about table degree_value. What columns, data types, and indexes (if any) does it have?
The DESC (or DESCRIBE) keyword will get you the columns and data types.
1 2 3 4 5 6 7 8 | mysql> DESC degree_value; +---------------+-----------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------------+-----------------------+------+-----+---------+-------+ | pipe_id | smallint(6) | YES | MUL | NULL | | | degree_amount | decimal(4,2) unsigned | YES | | NULL | | +---------------+-----------------------+------+-----+---------+-------+ 2 rows in set (0.00 sec) |
But, it leaves out any indexes. That’s where SHOW coupled with the CREATE TABLE command returns more information than DESC:
1 2 3 4 5 6 7 8 9 10 | mysql> SHOW CREATE TABLE degree_value\G *************************** 1. row *************************** Table: degree_value Create Table: CREATE TABLE `degree_value` ( `pipe_id` smallint(6) DEFAULT NULL, `degree_amount` decimal(4,2) unsigned DEFAULT NULL, KEY `degree_value_ibfk_1` (`pipe_id`), CONSTRAINT `degree_value_ibfk_1` FOREIGN KEY (`pipe_id`) REFERENCES `pipe` (`pipe_id`) ON DELETE SET NULL ON UPDATE CASCADE ) ENGINE=InnoDB DEFAULT CHARSET=latin1 1 row in set (0.02 sec) |
What user am I logged in as?
Try this:
1 2 3 4 5 6 7 | mysql> SELECT USER(); +------------------+ | USER() | +------------------+ | j2112o@localhost | +------------------+ 1 row in set (0.00 sec) |
To note: SELECT CURRENT_USER(); works as well.
What stored procedures or functions do I have written in this database? I vaguely remember a part of the name. Here you are:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 | mysql> SHOW PROCEDURE STATUS WHERE Db = 'asbuilt' AND Name LIKE '%short%'\G *************************** 1. row *************************** Db: asbuilt Name: proc_short_pipe Type: PROCEDURE Definer: j2112o@localhost Modified: 2018-06-26 10:34:08 Created: 2018-06-26 10:34:08 Security_type: DEFINER Comment: character_set_client: utf8 collation_connection: utf8_general_ci Database Collation: utf8mb4_unicode_ci 1 row in set (0.00 sec) |
You can then use CREATE PROCEDURE syntax with SHOW to retrieve details of the procedures definition:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 | mysql> SHOW CREATE PROCEDURE proc_short_pipe\G *************************** 1. row *************************** Procedure: proc_short_pipe sql_mode: ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION Create Procedure: CREATE DEFINER=`j2112o`@`localhost` PROCEDURE `proc_short_pipe`(IN p_wt_amt DECIMAL(4,3), OUT p_pipe_name VARCHAR(25), OUT p_pipe_length DECIMAL(4,2)) BEGIN DECLARE v_p_name VARCHAR(25); DECLARE v_length DECIMAL(4,2); SELECT p.pipe_name, p.pipe_length INTO v_p_name, v_length FROM pipe AS p INNER JOIN pw_wall_thickness AS pw ON p.pipe_id = pw.pw_pipe_id INNER JOIN wall_thickness AS wt ON pw.pw_thickness_id = wt.w_thickness_id WHERE wt.wall_thickness_amount = p_wt_amt ORDER BY p.pipe_length ASC LIMIT 1; SELECT CONCAT(v_p_name, ' has the shortest length of ', v_length); END character_set_client: utf8 collation_connection: utf8_general_ci Database Collation: utf8mb4_unicode_ci 1 row in set (0.01 sec) |
For more information, be sure and visit the SHOW Syntax Documentation page for other uses of SHOW.
These are but a few usage examples of SHOW. Explore the SHOW command more to discover its many uses to retrieve useful information. Feel free to share your comments below. Thanks for reading.
Explore the official MySQL 5.7 Online Manual for more information.
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Josh Otwell has a passion to study and grow as a SQL Developer and blogger. Other favorite activities find him with his nose buried in a good book, article, or the Linux command line. Among those, he shares a love of tabletop RPG games, reading fantasy novels, and spending time with his wife and two daughters.
Disclaimer: The examples presented in this post are hypothetical ideas of how to achieve similar types of results. They are not the utmost best solution(s). The majority, if not all, of the examples provided, are performed on a personal development/learning workstation-environment and should not be considered production quality or ready. Your particular goals and needs may vary. Use those practices that best benefit your needs and goals. Opinions are my own.
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