MySQL's Recursive CTE is mainly used to process hierarchical data. 1. It realizes traversal of the tree structure through initial queries and recursive queries, such as finding all subordinates of a certain employee; 2. It can be used to generate numerical sequences, such as 1 to 100; 3. When using them, be careful to avoid infinite loops, control recursive depth, optimize indexes, and first test small data to verify the correctness of the logic.
MySQL's Recursive CTE (recursive public table expression) is mainly used to process hierarchical data, such as organizational structure, classification trees, comment nesting, etc. Recursive CTE is very useful if you need to start from a node and find all its children or parents.
Here is a common example to illustrate how to use MySQL's Recursive CTE.
1. What is Recursive CTE?
CTE (Common Table Expression) is a temporary named result set that can be referenced in SQL queries. Recursive CTE is a special CTE that can repeatedly refer to itself, thereby realizing the traversal of hierarchical data.
In MySQL, the syntax structure of Recursive CTE is as follows:
WITH RECURSIVE cte_name AS (
-- Initial query (non-recursive part)
SELECT ...
UNION ALL
-- Recursive part SELECT ... FROM cte_name WHERE ...
)
SELECT * FROM cte_name;2. Example: Query the employees' subordinate teams
Suppose there is a employees table, the structure is as follows:
| id | name | manager_id |
|---|---|---|
| 1 | Alice | NULL |
| 2 | Bob | 1 |
| 3 | Carol | 2 |
| 4 | David | 2 |
| 5 | Eve | 1 |
Goal: Find all subordinates of Alice (id=1) (including both direct and indirect subordinates).
SQL queries are as follows:
WITH RECURSIVE subordinates AS (
-- Initial query: Find the SELECT id, name, manager_id of Alice
FROM employees
WHERE manager_id = 1
UNION ALL
-- Recursive query: Continue to find the subordinates' subordinates SELECT e.id, e.name, e.manager_id
FROM employees e
INNER JOIN subordinates s ON e.manager_id = s.id
)
SELECT * FROM subordinates;The execution results will include Bob, Carol, David, and Eve.
Note:
- The recursive termination condition is automatically terminated when no more records can be added.
-
manager_id = 1is just the starting point, you can change it to another ID according to your needs. - If the level is too deep, you may encounter performance problems or exceed the recursive depth limit (the default is 1000), which can be adjusted by setting
cte_max_recursion_depth.
3. Another common purpose: generate a sequence of numbers
Sometimes we need to generate a series of consecutive numbers, such as 1 to 100. Recursive CTE can also be used to do this.
WITH RECURSIVE numbers AS (
SELECT 1 AS n
UNION ALL
SELECT n 1 FROM numbers WHERE n < 100
)
SELECT * FROM numbers;Although this example is simple, it is very suitable for understanding recursive logic. You can also expand it to do more complex things, such as date sequences, time segment statistics, etc.
4. Several suggestions for using Recursive CTE
- Avoid infinite loops : Make sure that recursion has clear termination conditions, otherwise it will cause errors or query stuck.
- Control the depth of recursion : If the amount of data is large, appropriately limit the depth of recursion to avoid excessive resource consumption.
- Index optimization : Establishing indexes on recursive fields (such as parent_id, manager_id) can significantly improve performance.
- Test small data : First use a small amount of data to test whether the logic is correct, and then apply it to the full amount of data.
Basically that's all. Recursive CTE is very powerful when dealing with tree structures or hierarchical relationships. After mastering the basic structure, it can be flexibly applied to various scenarios.
The above is the detailed content of mysql recursive cte example. 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
Resetting the root password for MySQL server
Jul 03, 2025 am 02:32 AM
To reset the root password of MySQL, please follow the following steps: 1. Stop the MySQL server, use sudosystemctlstopmysql or sudosystemctlstopmysqld; 2. Start MySQL in --skip-grant-tables mode, execute sudomysqld-skip-grant-tables&; 3. Log in to MySQL and execute the corresponding SQL command to modify the password according to the version, such as FLUSHPRIVILEGES;ALTERUSER'root'@'localhost'IDENTIFIEDBY'your_new
Handling NULL Values in MySQL Columns and Queries
Jul 05, 2025 am 02:46 AM
When handling NULL values ??in MySQL, please note: 1. When designing the table, the key fields are set to NOTNULL, and optional fields are allowed NULL; 2. ISNULL or ISNOTNULL must be used with = or !=; 3. IFNULL or COALESCE functions can be used to replace the display default values; 4. Be cautious when using NULL values ??directly when inserting or updating, and pay attention to the data source and ORM framework processing methods. NULL represents an unknown value and does not equal any value, including itself. Therefore, be careful when querying, counting, and connecting tables to avoid missing data or logical errors. Rational use of functions and constraints can effectively reduce interference caused by NULL.
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.
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.
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
Aggregating data with GROUP BY and HAVING clauses in MySQL
Jul 05, 2025 am 02:42 AM
GROUPBY is used to group data by field and perform aggregation operations, and HAVING is used to filter the results after grouping. For example, using GROUPBYcustomer_id can calculate the total consumption amount of each customer; using HAVING can filter out customers with a total consumption of more than 1,000. The non-aggregated fields after SELECT must appear in GROUPBY, and HAVING can be conditionally filtered using an alias or original expressions. Common techniques include counting the number of each group, grouping multiple fields, and filtering with multiple conditions.
Managing Transactions and Locking Behavior in MySQL
Jul 04, 2025 am 02:24 AM
MySQL transactions and lock mechanisms are key to concurrent control and performance tuning. 1. When using transactions, be sure to explicitly turn on and keep the transactions short to avoid resource occupation and undolog bloating due to long transactions; 2. Locking operations include shared locks and exclusive locks, SELECT...FORUPDATE plus X locks, SELECT...LOCKINSHAREMODE plus S locks, write operations automatically locks, and indexes should be used to reduce the lock granularity; 3. The isolation level is repetitively readable by default, suitable for most scenarios, and modifications should be cautious; 4. Deadlock inspection can analyze the details of the latest deadlock through the SHOWENGINEINNODBSTATUS command, and the optimization methods include unified execution order, increase indexes, and introduce queue systems.
Paginating Results with LIMIT and OFFSET in MySQL
Jul 05, 2025 am 02:41 AM
MySQL paging is commonly implemented using LIMIT and OFFSET, but its performance is poor under large data volume. 1. LIMIT controls the number of each page, OFFSET controls the starting position, and the syntax is LIMITNOFFSETM; 2. Performance problems are caused by excessive records and discarding OFFSET scans, resulting in low efficiency; 3. Optimization suggestions include using cursor paging, index acceleration, and lazy loading; 4. Cursor paging locates the starting point of the next page through the unique value of the last record of the previous page, avoiding OFFSET, which is suitable for "next page" operation, and is not suitable for random jumps.
