Analysis of MySQL Window Function Practical Case
Apr 08, 2025 am 09:51 AM
MySQL window function: It's not just ranking
Many friends think that MySQL's window function (Window Function) is only used for ranking, but it is not. It has many things to do! In this article, let’s talk about the window functions, from basic to advanced usage, and then to some pitfalls, to help you master this weapon thoroughly. After reading it, you can not only easily deal with various ranking scenarios, but also flexibly use it to solve more complex data analysis problems, and even write more elegant and efficient SQL than others.
Let me talk about the basics first. A window function, simply put, calculates a set of data, but does not "compress" the data into a row like the aggregate function, but retains the number of rows of the original data and adds calculation results for each row. This is like a moving "window" that slides in the dataset, calculating a portion of the data at a time.
For example, suppose there is an order table containing the order ID, customer ID and order amount. You want to know how much order amounts per customer rank among all customer order amounts. At this time, RANK() function comes in handy:
<code class="sql">SELECT</code><pre class='brush:php;toolbar:false;'> order_id, customer_id, order_amount, RANK() OVER (ORDER BY order_amount DESC) as rank
FROM
orders;</code>
This code assigns a ranking to each order, sorting from high to low according to the order amount. OVER (ORDER BY order_amount DESC) This part is the "rules" that define the window, telling the function how to "move" the window.
However, the RANK() function has a minor flaw: if multiple orders have the same amount, they will get the same ranking, causing the ranking to jump. For example, if there are two orders with a total amount of 100 and they are both ranked first, then the next order will be ranked 3 instead of 2. At this time, you can consider using DENSE_RANK(), which will not skip rankings, or use ROW_NUMBER(), which will assign a unique sequence number to each row, regardless of whether the order amount is the same. Which function to choose depends on your specific needs. It's like choosing a tool, it depends on the situation.
Let’s take a look at some advanced ones. The window function can combine the PARTITION BY clause to perform group calculations on the data. For example, you want to know how much order amounts for each customer are ranked within their customers:
SELECT order_id, customer_id, order_amount, RANK() OVER (PARTITION BY customer_id ORDER BY order_amount DESC) as customer_rank
FROM
orders;
Here, PARTITION BY customer_id group data by customer ID and then rank and calculate within each group. It's like dividing the data into multiple "windows", each "window" independently computes rankings.
In addition to ranking, window functions can do many other things, such as calculating cumulative sums, moving averages, lag values, etc. For example, calculate the cumulative order amount for each customer:
SELECT order_id, customer_id, order_amount, SUM(order_amount) OVER (PARTITION BY customer_id ORDER BY order_id) as cumulative_amount
FROM
orders;
Here, the SUM() function is used as a window function to calculate the cumulative order amount for each customer. ORDER BY order_id specifies the order of accumulation.
Of course, there are some things to pay attention to when using window functions. For example, the performance of window functions may be affected by the amount of data, especially when dealing with large data sets. Therefore, in practical applications, it is necessary to select appropriate window functions and optimization strategies according to specific circumstances. Sometimes, a simple subquery may be more efficient than a window function. This requires you to test and select according to actual conditions.
Lastly, what I want to say is that mastering window functions can make you feel at ease in the field of data analysis. It is not only a simple ranking tool, but also a powerful data processing tool that can help you solve many complex data problems. Practice more and try more, and you will find more of its magical uses. Remember, the elegance and efficiency of code are the ultimate pursuit of programmers!
The above is the detailed content of Analysis of MySQL Window Function Practical Case. 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
Choosing appropriate data types for columns in MySQL tables
Jul 15, 2025 am 02:25 AM
WhensettingupMySQLtables,choosingtherightdatatypesiscrucialforefficiencyandscalability.1)Understandthedataeachcolumnwillstore—numbers,text,dates,orflags—andchooseaccordingly.2)UseCHARforfixed-lengthdatalikecountrycodesandVARCHARforvariable-lengthdata
Setting up semi-synchronous replication in MySQL
Jul 15, 2025 am 02:35 AM
The steps for setting MySQL semi-synchronous replication are as follows: 1. Confirm the version supports and load the plug-in; 2. Turn on and enable semi-synchronous mode; 3. Check the status and operation status; 4. Pay attention to timeout settings, multi-slave library configuration and master-slave switching processing. It is necessary to ensure that MySQL 5.5 and above versions are installed, rpl_semi_sync_master and rpl_semi_sync_slave plugins, enable corresponding parameters in the master and slave library, and configure automatic loading in my.cnf, restart the service after the settings are completed, check the status through SHOWSTATUS, reasonably adjust the timeout time and monitor the plug-in operation.
LayerZero, StarkNet, ZK Ecological Preheat: How long can the airdrop bonus last?
Jul 16, 2025 am 10:06 AM
The duration of the airdrop dividend is uncertain, but the LayerZero, StarkNet and ZK ecosystems still have long-term value. 1. LayerZero achieves cross-chain interoperability through lightweight protocols; 2. StarkNet provides efficient and low-cost Ethereum L2 expansion solutions based on ZK-STARKs technology; 3. ZK ecosystem (such as zkSync, Scroll, etc.) expands the application of zero-knowledge proof in scaling and privacy protection; 4. Participation methods include the use of bridging tools, interactive DApps, participating test networks, pledged assets, etc., aiming to experience the next generation of blockchain infrastructure in advance and strive for potential airdrop opportunities.
mysql incorrect string value for column
Jul 15, 2025 am 02:40 AM
MySQL error "incorrectstringvalueforcolumn" is usually because the field character set does not support four-byte characters such as emoji. 1. Cause of error: MySQL's utf8 character set only supports three-byte characters and cannot store four-byte emoji; 2. Solution: Change the database, table, fields and connections to utf8mb4 character set; 3. Also check whether the configuration files, temporary tables, application layer encoding and client drivers all support utf8mb4; 4. Alternative solution: If you do not need to support four-byte characters, you can filter special characters such as emoji at the application layer.
The flow of funds on the chain is exposed: What new tokens are being bet on by Clever Money?
Jul 16, 2025 am 10:15 AM
Ordinary investors can discover potential tokens by tracking "smart money", which are high-profit addresses, and paying attention to their trends can provide leading indicators. 1. Use tools such as Nansen and Arkham Intelligence to analyze the data on the chain to view the buying and holdings of smart money; 2. Use Dune Analytics to obtain community-created dashboards to monitor the flow of funds; 3. Follow platforms such as Lookonchain to obtain real-time intelligence. Recently, Cangming Money is planning to re-polize LRT track, DePIN project, modular ecosystem and RWA protocol. For example, a certain LRT protocol has obtained a large amount of early deposits, a certain DePIN project has been accumulated continuously, a certain game public chain has been supported by the industry treasury, and a certain RWA protocol has attracted institutions to enter.
how to connect to mysql from node.js
Jul 14, 2025 am 02:35 AM
To connect MySQL data to Node.js application, 1. Install the mysql2 module; 2. Create a connection configuration, including host, user, password, database and other information; 3. Establish a connection and handle errors; 4. Execute SQL queries and process results; 5. Close the connection or use the connection pool to manage the connection; Common problems include network blockage, insufficient account permissions, firewall restrictions, password errors and SSL connection problems. Follow the steps to troubleshoot.
How to get back the bitcoin I bought before? Tutorial for retrieving bitcoin
Jul 15, 2025 pm 07:09 PM
To retrieve Bitcoins purchased years ago, you must first determine its storage location and retrieve the access key. The specific steps are as follows: 1. Recall and check the exchange accounts you may have used, such as Binance, Ouyi, Huobi, Gate.io, Coinbase, Kraken, etc., and try to log in or retrieve your password through email; 2. If Bitcoin has been withdrawn to your personal wallet, you must find the mnemonic, private key or wallet file. This information may exist in physical backup, electronic device or password manager; 3. After finding the key information, use the mainstream wallet app to select the "Recover Wallet" function and accurately enter the mnemonic or private key to synchronize the assets; Important tips: Do not disclose mnemonic or private keys to ensure the safe operation environment, and patiently and systematically check all
The top ten currency trading platform apps in the world
Jul 15, 2025 pm 08:27 PM
The top ten popular digital currency trading platforms in the world include Binance, Ouyi OKX, gate.io, Huobi, KuCoin, Kraken, Bitfinex and Bitstamp. 1. Binance is known for its large trading volume, rich trading pairs, multi-trading mode, high security and user-friendly; 2. Ouyi OKX provides diversified derivatives, localized services, stable technology and Web3 layout; 3. gate.io has the advantages of strict project screening, many trading products, strong compliance, diverse financial products and simple interface; 4. Huobi has mainstream trading products, complete security guarantees, rich activities and localized operations; 5. KuCoin focuses on potential currencies, diversified trading tools, platform currency benefits and multi-language support; 6
