How to calculate the number of immediate children for each node in an adjacency list

Posted by Travis on Stack Overflow See other posts from Stack Overflow or by Travis
Published on 2010-06-15T03:10:06Z Indexed on 2010/06/15 3:12 UTC
Read the original article Hit count: 319

Filed under:

mysql

|

select

|

mysql-query

|

adjacency-list

I have hierarchical data that I represent using the adjacency list model.

TABLE
    ID
    parentID
    title

I am wondering, what is the simplest way to SELECT the number of immediate children for each node? If possible, I'd like to do this in a single select, yielding a resultset like so...

RESULTS...
ID     title     childCount
1      test1     10
2      test2     2
3      test3     0
etc...

Thanks for your advice!

© Stack Overflow or respective owner

Related posts about mysql

How to remove MySQL completely with config and library files on ubuntu 12.04 gnome 3.0

as seen on Ask Ubuntu - Search for 'Ask Ubuntu'
I tried everything till now: sudo apt-get remove mysql-server mysql-client mysql-common sudo apt-get purge mysql-server mysql-client mysql-common sudo apt-get autoremove and even more commands... But whenever I am trying to locate mysql. I get a no. of files related to mysql command: shell>>… >>> More
mysql: Cannot load from mysql.proc. The table is probably corrupted

as seen on Server Fault - Search for 'Server Fault'
Mysql was started: /usr/bin/mysqld_safe --datadir=/srv/mysql/myDB --log-error=/srv/mysql/logs/mysqld-myDB.log --pid-file=/srv/mysql/pids/mysqld-myDB.pid --user=mysql --socket=/srv/mysql/sockets/mysql-myDB.sock --port=3700 but when I'm trying to do something: ERROR 1548 (HY000) at line 1: Cannot… >>> More
Why is there a /etc/init.d/mysql file on this Slackware machine? How could it have gotten there?

as seen on Server Fault - Search for 'Server Fault'
A client of my IT-consulting service owns a web-development shop. He's been having problems with a Slackware 12.0 server running MySQL 5.0.67. The machine was set up by the client's sysadmin, who left on bad terms. My client no longer employs a sysadmin. As far as I can tell, the only copy of MySQL… >>> More
mysql: Bind on unix socket: Permission denied

as seen on Server Fault - Search for 'Server Fault'
Can't start mysql with: sudo /usr/bin/mysqld_safe --datadir=/srv/mysql/myDB --log-error=/srv/mysql/logs/mysqld-myDB.log --pid-file=/srv/mysql/pids/mysqld-myDB.pid --user=mysql --socket=/srv/mysql/sockets/mysql-myDB.sock --port=3700 120222 13:40:48 mysqld_safe Starting mysqld daemon with databases… >>> More
MySQL – Learning MySQL Online in 6 Hours – MySQL Fundamentals in 320 Minutes

as seen on SQL Authority - Search for 'SQL Authority'
MySQL is one of the most popular database language and I have been recently working with it a lot. Data have no barrier and every database have their own place. I have been working with MySQL for quite a while and just like SQL Server, I often find lots of people asking me if I have a tutorial which… >>> More

Related posts about select

HTML muliple select should look like HTML select

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi I am trying to use a HTML select box with 'multiple' select options and size to 1 as below ` <SELECT NAME="toppings" MULTIPLE SIZE=5> <OPTION VALUE="mushrooms">mushrooms <OPTION VALUE="greenpeppers">green peppers </SELECT> When the size is set to 1 small scrollbar appears… >>> More
MySQL Query Select using sub-select takes too long

as seen on Stack Overflow - Search for 'Stack Overflow'
I noticed something strange while executing a select from 2 tables: SELECT * FROM table_1 WHERE id IN ( SELECT id_element FROM table_2 WHERE column_2=3103); This query took approximatively 242 seconds. But when I executed the subquery SELECT id_element FROM table_2 WHERE column_2=3103 it… >>> More
SQL SERVER- IF EXISTS(Select null from table) vs IF EXISTS(Select 1 from table)

as seen on SQL Authority - Search for 'SQL Authority'
Few days ago I wrote article about SQL SERVER – Stored Procedure Optimization Tips – Best Practices. I received lots of comments on particular blog article. In fact, almost all the comments are very interesting. If you have not read all the comments, I strongly suggest to read them. Click here to… >>> More
Nesting Linq-to-Objects query within Linq-to-Entities query –what is happening under the covers?

as seen on Programmers - Search for 'Programmers'
var numbers = new int[] { 1, 2, 3, 4, 5 }; var contacts = from c in context.Contacts where c.ContactID == numbers.Max() | c.ContactID == numbers.FirstOrDefault() select c; foreach (var item in contacts) Console.WriteLine(item.ContactID); Linq-to-Entities… >>> More
Play Framework: Error getting sequence nextval using H2 in-memory database

as seen on Stack Overflow - Search for 'Stack Overflow'
As the title suggests, I get an error running Play 2.0.1 Tests using a FakeApplication w/ H2 in memory. I set up a basic unit test: public class ModelTest { @Test public void checkThatIndustriesExist() { running(fakeApplication(inMemoryDatabase()), new Runnable() { public… >>> More