Databases
StackOverflow2013
Postsdbo
POUsing MySQL, What is the best way to not to select users that exist in a different table?
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POUsing MySQL, What is the best way to not to select users that exist in a different table?
    primarykey
    data
    text
    <p>My problem is the following: I have two tables; persons and teams, I want to select all the persons with role_id = 2, that exist in <code>persons</code> but <strong>not</strong> in teams.</p> <p>Table <code>teams</code> stores the hashes for the <em>team leader</em> who can only lead <strong>one</strong> team at a time. When creating teams, I just want to show administrators the people who is not currently leading a team, basically exclude all the ones who are already leaders of any given team.</p> <p>My structure is as follows:</p> <pre><code>mysql&gt; desc persons; +-------------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +------------+-------------+------+-----+---------+-------+ | firstname | varchar(9) | YES | | NULL | | | lastname | varchar(10) | YES | | NULL | | | role_id | int(2) | YES | | NULL | | | hash | varchar(32) | NO | UNI | NULL | | +-------------+-------------+------+-----+---------+-------+ mysql&gt; desc teams; +--------+-------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +--------+-------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | name | varchar(20) | YES | | NULL | | | leader | varchar(32) | NO | | NULL | | +--------+-------------+------+-----+---------+----------------+ 3 rows in set (0.00 sec) </code></pre> <p>My current SQL is as follows:</p> <pre><code>SELECT CONCAT( `persons`.`firstname` ," ", `persons`.`lastname` ) AS `manager`, `hash` FROM `persons` WHERE `persons`.`role_id` =2 AND `persons`.`hash` != (SELECT `leader` FROM `teams` ); </code></pre> <p>The latter SQL Query works when the table <code>teams</code> only has 1 record, but as soon as I add another one, MySQL complaints about the subquery producing two records.</p> <p>In the <strong>WHERE</strong> Clause, instead of subqueries I've also tried the following:</p> <pre><code> WHERE `persons`.`role_id` = 2 AND `persons`.`hash` != `teams`.`leader` </code></pre> <p>but then it complaints about column <code>leader</code> not existing in table <code>teams</code></p> <p>I was also thinking about using some kind of <em>inverse</em> LEFT JOIN, but I haven't been able to come up with an optimal solution.</p> <p>Any help is greatly appreciated! Thanks</p> <p><strong>P.S.</strong>: Here is the SQL statements should you want to have a scenario similar to mine:</p> <pre><code>DROP TABLE IF EXISTS `teams`; CREATE TABLE IF NOT EXISTS `teams` ( `id` int(11) NOT NULL AUTO_INCREMENT, `name` varchar(20) DEFAULT NULL, `leader` varchar(32) NOT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 AUTO_INCREMENT=3 ; INSERT INTO `teams` (`id`, `name`, `leader`) VALUES (1, 'Team 1', '406a3f5892e0fcb22bfc81ae023ce252'), (2, 'Team 2', 'd0ca479152996c8cabd89151fe844e63'); DROP TABLE IF EXISTS `persons`; CREATE TABLE IF NOT EXISTS `persons` ( `firstname` varchar(9) DEFAULT NULL, `lastname` varchar(10) DEFAULT NULL, `role_id` int(2) DEFAULT NULL, `hash` varchar(32) NOT NULL, PRIMARY KEY `hash` (`hash`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8; INSERT INTO `persons` (`firstname`, `lastname`, `role_id`,`hash`) VALUES ('John', 'Doe', 2, '406a3f5892e0fcb22bfc81ae023ce252'), ('Jane', 'Doe', 2, 'd0ca479152996c8cabd89151fe844e63'), ('List', 'Me', 2, 'fbde2c4eeee7f455b655fe4805cfe66a'), ('List', 'Me Too', 2, '6dee2c4efae7f452b655abb805cfe66a'); </code></pre>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. This table or related slice is empty.
    1. USILikeTacos
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POUsing MySQL, What is the best way to not to select users that exist in a different table?
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POUsing MySQL, What is the best way to not to select users that exist in a different table?
      1. This table or related slice is empty.
      1. VTUpMod
    1. COtry to JOIN tables in your select query
      singulars
      1. POUsing MySQL, What is the best way to not to select users that exist in a different table?
      1. USdebianek
    2. COThank you for your answer, but JOIN-ing tables would only give me the persons that exists in `persons` **and** `teams`, in other words; team leaders.
      singulars
      1. POUsing MySQL, What is the best way to not to select users that exist in a different table?
      1. USILikeTacos
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload