MYSQL Dense Rank Trigger or Update Statement

MySQL

I have a MYSQL table that I need to rank. Each group of child_no needs to be ranked by Parent_NO. I have a select statement see below, that successfully does the ranking. Now I'm looking at at taking the results of the select and actually updating the table. I would ideally like to do this with a trigger on insert,else an update statement that I can run manually will suffice.

Any help on formulating either option would be greatly appreciated. See example on sqlfiddle (I've added an auto id, and target rank column in by statements below): http://sqlfiddle.com/#!9/ebe33/18

Table

CREATE TABLE ranktest
(`parent_no` varchar(10), 
 `child_no` varchar(10), 
 `rankfinal` int,
 `id`   MEDIUMINT NOT NULL AUTO_INCREMENT, 
  PRIMARY KEY (id)
);

INSERT INTO ranking
(`parent_no`, `child_no`)
VALUES
('1234', '20'),
('1234', '21'),
('1234', '21'),
('9845', '50'),
('9845', '50'),
('9845', '52'),
('9845', '52'),
('9845', '53'),
('9845', '53'),
('9845', '55'),
('5678', '60'),
('2468', '10'),
('2468', '10');

Select Statement to gather rank

set @rank = 0;
set @prev_child = NULL;
set @prev_parent = NULL;
select parent_no, child_no, rank from (
    select parent_no, child_no, CASE
     when @prev_parent != parent_no then @rank := 1 
     when @prev_child = child_no then @rank
     else @rank := @rank + 1
END as rank,   @prev_parent:= parent_no, @prev_child:=child_no
from ranktest
order by parent_no, child_no
) as rankcalc

Best Answer

Switch to MariaDB 10.2 and use their "dense rank" windowing function.

https://mariadb.com/kb/en/mariadb/dense_rank/

Related Solutions

Mysql – Drop auto increment hack w/o alter table

I tried something similar just now

Here is MySQL for My PC

mysql> select * from information_schema.global_variables where variable_name='datadir' or variable_name like 'versio%';
+-------------------------+------------------------------+
| VARIABLE_NAME           | VARIABLE_VALUE               |
+-------------------------+------------------------------+
| VERSION_COMMENT         | MySQL Community Server (GPL) |
| VERSION                 | 5.5.12-log                   |
| VERSION_COMPILE_MACHINE | x86                          |
| DATADIR                 | C:\MySQL_5.5.12\data\        |
| VERSION_COMPILE_OS      | Win64                        |
+-------------------------+------------------------------+
5 rows in set (0.00 sec)

I will run this using MyISAM

Step 01) create a table called 'rolando'
Step 02) insert 'dominique' and 'diamond'
Step 03) copy the table structure to 'pamela'
Step 04) alter 'pamela' to not have auto_increment
Step 05) In DOS, copy rolando.MYD to pamela.MYD
Step 06) run REPAIR TABLE pamela; (Rebuild pamela.MYI)
Step 07) run SELECT COUNT(1) FROM pamela;
Step 08) run SHOW CREATE TABLE pamela\G
Step 09) run SELECT * FROM pamela;
Step 10) insert 'carlik' into pamela
Step 11) run SELECT * FROM pamela;

Let's see if these steps are kosher.

Here are Steps 1-4

mysql> drop table if exists rolando;
Query OK, 0 rows affected (0.02 sec)

mysql> drop table if exists pamela;
Query OK, 0 rows affected (0.00 sec)

mysql> create table rolando
    -> (
    ->     name varchar(20),
    ->     id int not null auto_increment,
    ->     primary key (id)
    -> ) ENGINE=MyISAM;
Query OK, 0 rows affected (0.05 sec)

mysql> insert into rolando (name) values ('dominique'),('diamond');
Query OK, 2 rows affected (0.00 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> select * from rolando;
+-----------+----+
| name      | id |
+-----------+----+
| dominique |  1 |
| diamond   |  2 |
+-----------+----+
2 rows in set (0.00 sec)

mysql> create table pamela like rolando;
Query OK, 0 rows affected (0.05 sec)

mysql> show create table rolando\G
*************************** 1. row ***************************
       Table: rolando
Create Table: CREATE TABLE `rolando` (
  `name` varchar(20) DEFAULT NULL,
  `id` int(11) NOT NULL AUTO_INCREMENT,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=3 DEFAULT CHARSET=latin1
1 row in set (0.00 sec)

mysql> show create table pamela\G
*************************** 1. row ***************************
       Table: pamela
Create Table: CREATE TABLE `pamela` (
  `name` varchar(20) DEFAULT NULL,
  `id` int(11) NOT NULL AUTO_INCREMENT,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1
1 row in set (0.02 sec)

mysql> alter table pamela modify id int(11) unsigned not null;
Query OK, 0 rows affected (0.11 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show create table pamela\G
*************************** 1. row ***************************
       Table: pamela
Create Table: CREATE TABLE `pamela` (
  `name` varchar(20) DEFAULT NULL,
  `id` int(11) unsigned NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1
1 row in set (0.00 sec)

mysql> select count(1) from pamela;
+----------+
| count(1) |
+----------+
|        0 |
+----------+
1 row in set (0.01 sec)

mysql>

Here is Step 6

C:\>copy C:\MySQL_5.5.12\data\test\rolando.MYD C:\MySQL_5.5.12\data\test\pamela.MYD
        1 file(s) copied.

C:\>

Here are the rest of the Steps starting at Step 7

mysql> repair table pamela;
+-------------+--------+----------+------------------------------------+
| Table       | Op     | Msg_type | Msg_text                           |
+-------------+--------+----------+------------------------------------+
| test.pamela | repair | warning  | Number of rows changed from 0 to 2 |
| test.pamela | repair | status   | OK                                 |
+-------------+--------+----------+------------------------------------+
2 rows in set (0.03 sec)

mysql> select count(1) from pamela;
+----------+
| count(1) |
+----------+
|        2 |
+----------+
1 row in set (0.00 sec)

mysql> insert into pamela (name,id) values ('carlik',3);
Query OK, 1 row affected (0.00 sec)

mysql> select * from pamela;
+-----------+----+
| name      | id |
+-----------+----+
| dominique |  1 |
| diamond   |  2 |
| carlik    |  3 |
+-----------+----+
3 rows in set (0.00 sec)

mysql>

Dangerous game, isn't it ???

Guess what? Stuff like this is actually published in "High Performance MySQL : Optimization, Backups, Replication, and more", Pages 146-148 under the Subheading Speeding Up ALTER TABLE. Page 147 Paragraph 1 says:

The technique we are about to demonstrate is unsupported, undocumented, and may not work. Use it at your risk. We advise you to back up you data first!

I also had an earlier post when someone ask a similar question : Can I rename the values in a MySQL ENUM column in one query?

You got guts, @atxdba !!!

Mysql – find and insert row to another table using thesql trigger

This should do the trick for you:

DELIMITER $$
DROP TRIGGER IF EXISTS `employee_INSERT` $$
CREATE TRIGGER `employee_INSERT` 
AFTER INSERT ON `employee`
FOR EACH ROW
BEGIN
    INSERT INTO employee_tools (Id, Tool)
    SELECT new.Id, tools.Tool_Name 
            FROM tools
            WHERE tools.Division = new.Division;
END $$
DELIMITER ;

Best Answer

Related Solutions

Mysql – Drop auto increment hack w/o alter table

Mysql – find and insert row to another table using thesql trigger

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