Database
Mysql Tutorial
How to Recursively Query a Tree Structure in MySQL to Find Descendants of a Parent Node?
How to Recursively Query a Tree Structure in MySQL to Find Descendants of a Parent Node?
Oct 24, 2024 am 04:20 AM
Recursing a Tree Structure in MySQL
Managing hierarchical data can be a challenge in relational databases, especially when recursive querying is required. In MySQL, we have a specific problem: how to efficiently retrieve all descendants of a given parent location, no matter the depth of the hierarchy.
The Problem:
Consider the following database schema for locations:
location (id, ....) location_parent (location_id, parent_id)
The location table stores location information, while the location_parent table defines the parent-child relationship between locations.
Suppose we have a location with ID 5. We want to retrieve all its descendants, including those that are multiple levels deep.
Initial Solution:
One approach to recursive querying is to use a self-join as follows:
<code class="sql">SELECT DISTINCT l.id FROM location AS l LEFT JOIN location_parent AS lp ON l.id = lp.child_id WHERE lp.parent_id = 5 ;</code>
This query will retrieve the direct children of location 5. However, for deeper descendants, we need to repeat the query multiple times, each time using the results of the previous query as the input for the next. This method is inefficient and impractical for large hierarchical structures.
Recommended Solution:
The recommended solution to this problem is to use the recursive Common Table Expression (CTE). A CTE is a temporary table that can be defined and referenced within a single query.
<code class="sql">WITH RECURSIVE descendants AS (
SELECT id, parent_id
FROM location_parent
WHERE parent_id = 5
UNION ALL
SELECT lp.child_id, lp.parent_id
FROM descendants AS d
JOIN location_parent AS lp ON d.id = lp.parent_id
)
SELECT id
FROM descendants
;</code>
This query creates a recursive CTE called descendants, which starts with the direct children of location 5. The UNION ALL clause then adds the children of the previously selected descendants, effectively expanding the query to include all descendants at any depth.
The second part of the query selects the id column from the descendants CTE, which gives us the list of all descendant locations. This approach is much more efficient than the self-join method and can handle hierarchical structures of any depth.
The above is the detailed content of How to Recursively Query a Tree Structure in MySQL to Find Descendants of a Parent Node?. For more information, please follow other related articles on the PHP Chinese website!
Hot AI Tools
Undress AI Tool
Undress images for free
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
Establishing secure remote connections to a MySQL server
Jul 04, 2025 am 01:44 AM
TosecurelyconnecttoaremoteMySQLserver,useSSHtunneling,configureMySQLforremoteaccess,setfirewallrules,andconsiderSSLencryption.First,establishanSSHtunnelwithssh-L3307:localhost:3306user@remote-server-Nandconnectviamysql-h127.0.0.1-P3307.Second,editMyS
What are the ACID properties of a MySQL transaction?
Jun 20, 2025 am 01:06 AM
MySQL transactions follow ACID characteristics to ensure the reliability and consistency of database transactions. First, atomicity ensures that transactions are executed as an indivisible whole, either all succeed or all fail to roll back. For example, withdrawals and deposits must be completed or not occur at the same time in the transfer operation; second, consistency ensures that transactions transition the database from one valid state to another, and maintains the correct data logic through mechanisms such as constraints and triggers; third, isolation controls the visibility of multiple transactions when concurrent execution, prevents dirty reading, non-repeatable reading and fantasy reading. MySQL supports ReadUncommitted and ReadCommi.
How to add the MySQL bin directory to the system PATH
Jul 01, 2025 am 01:39 AM
To add MySQL's bin directory to the system PATH, it needs to be configured according to the different operating systems. 1. Windows system: Find the bin folder in the MySQL installation directory (the default path is usually C:\ProgramFiles\MySQL\MySQLServerX.X\bin), right-click "This Computer" → "Properties" → "Advanced System Settings" → "Environment Variables", select Path in "System Variables" and edit it, add the MySQLbin path, save it and restart the command prompt and enter mysql--version verification; 2.macOS and Linux systems: Bash users edit ~/.bashrc or ~/.bash_
What are the transaction isolation levels in MySQL, and which is the default?
Jun 23, 2025 pm 03:05 PM
MySQL's default transaction isolation level is RepeatableRead, which prevents dirty reads and non-repeatable reads through MVCC and gap locks, and avoids phantom reading in most cases; other major levels include read uncommitted (ReadUncommitted), allowing dirty reads but the fastest performance, 1. Read Committed (ReadCommitted) ensures that the submitted data is read but may encounter non-repeatable reads and phantom readings, 2. RepeatableRead default level ensures that multiple reads within the transaction are consistent, 3. Serialization (Serializable) the highest level, prevents other transactions from modifying data through locks, ensuring data integrity but sacrificing performance;
Where does mysql workbench save connection information
Jun 26, 2025 am 05:23 AM
MySQLWorkbench stores connection information in the system configuration file. The specific path varies according to the operating system: 1. It is located in %APPDATA%\MySQL\Workbench\connections.xml in Windows system; 2. It is located in ~/Library/ApplicationSupport/MySQL/Workbench/connections.xml in macOS system; 3. It is usually located in ~/.mysql/workbench/connections.xml in Linux system or ~/.local/share/data/MySQL/Wor
Performing logical backups using mysqldump in MySQL
Jul 06, 2025 am 02:55 AM
mysqldump is a common tool for performing logical backups of MySQL databases. It generates SQL files containing CREATE and INSERT statements to rebuild the database. 1. It does not back up the original file, but converts the database structure and content into portable SQL commands; 2. It is suitable for small databases or selective recovery, and is not suitable for fast recovery of TB-level data; 3. Common options include --single-transaction, --databases, --all-databases, --routines, etc.; 4. Use mysql command to import during recovery, and can turn off foreign key checks to improve speed; 5. It is recommended to test backup regularly, use compression, and automatic adjustment.
What is the principle behind a database connection pool?
Jun 20, 2025 am 01:07 AM
Aconnectionpoolisacacheofdatabaseconnectionsthatarekeptopenandreusedtoimproveefficiency.Insteadofopeningandclosingconnectionsforeachrequest,theapplicationborrowsaconnectionfromthepool,usesit,andthenreturnsit,reducingoverheadandimprovingperformance.Co
Analyzing the MySQL Slow Query Log to Find Performance Bottlenecks
Jul 04, 2025 am 02:46 AM
Turn on MySQL slow query logs and analyze locationable performance issues. 1. Edit the configuration file or dynamically set slow_query_log and long_query_time; 2. The log contains key fields such as Query_time, Lock_time, Rows_examined to assist in judging efficiency bottlenecks; 3. Use mysqldumpslow or pt-query-digest tools to efficiently analyze logs; 4. Optimization suggestions include adding indexes, avoiding SELECT*, splitting complex queries, etc. For example, adding an index to user_id can significantly reduce the number of scanned rows and improve query efficiency.
