Whether mysql foreign key creates an index
Apr 08, 2025 pm 04:21 PM
Foreign key constraints create indexes by default, but whether the index is efficient depends on the application scenario. If foreign key columns are often used for joining queries, the default index is sufficient; otherwise, foreign key constraints need to be disabled or more appropriate indexes are created manually. MySQL's foreign key index is usually a B-tree index, which is suitable for range queries and equivalent queries; for specific query modes, other index types can be considered or foreign key constraints are not used. Database optimization is an iterative process that should be tested and adjusted according to actual conditions, and the execution plan should be analyzed using the EXPLAIN statement to find performance bottlenecks, and then optimized in a targeted manner.
MySQL foreign key: index? Not indexed? This question is not that simple!
Many novices, even some veteran drivers, are confused about whether to create indexes for MySQL foreign keys. The answer is: Not necessarily! This is not a trick to you. Optimization of relational databases has never been a simple "yes" or "no".
We broke this article and talked about the things between MySQL foreign keys and indexes. After reading it, you will understand when to build an index, when to consider carefully, or even not to build it.
Let’s talk about the basics first. Foreign keys, simply put, are used to ensure data integrity. It ensures consistency of data between related tables, such as order tables and customer tables. The foreign key of the order table points to the primary key of the customer table, so that each order corresponds to an existing customer. By understanding this, you will understand the constraints of foreign keys, which itself limits the arbitrary nature of the data.
What about the index? It's like a catalog of books, allowing you to quickly find what you need. MySQL uses indexes to speed up data retrieval, but the index itself also needs to take up space, and maintaining the index also requires resources. Therefore, the more indexes, the better.
So, what is the relationship between foreign keys and indexes? Foreign key constraints themselves implicitly create indexes, which is the default behavior of many database systems. MySQL is no exception, it automatically creates an index on the foreign key column, usually a B-tree index. This means that when you create a foreign key, you usually don't need to manually create an index.
However, this does not mean that you can completely ignore the indexing problem. Whether the index created by default is efficient enough depends on your specific application scenario. If your foreign key column is often used for joining queries, this default index is enough, which can significantly improve query efficiency.
But if your foreign key columns are rarely used for querying, or your table is very small, then this default index will become a burden. It takes up extra storage space and adds additional overhead when inserting, updating, and deleting data. At this point, you may want to consider disabling foreign key constraints, or manually creating a more appropriate index.
For example, suppose there is a large order table with a foreign key pointing to a relatively small customer table. At this time, it is very necessary to create an index on the foreign key column of the order table, which can greatly speed up order query. However, if your customer table is very small, even with only a few hundred records, the performance gains from creating indexes on the foreign key column of the order table may be minimal, and it is not even as good as not to create an index.
To go a little further, MySQL's foreign key index type is usually a B-tree index, which is suitable for range queries and equivalent queries. But if your query mode is special, such as frequent full-text search, then B-tree index may not be the best choice. At this time, you may need to consider other index types, or simply not use foreign key constraints.
Finally, I would like to emphasize one thing: database optimization is an iterative process, without universal best practices. You need to test and adjust according to your actual situation. You can use the EXPLAIN statement to analyze the execution plan of your SQL statement, find performance bottlenecks, and then optimize in a targeted manner. Remember, performance optimization is a process of continuous learning and improvement.
Here is a simple example that demonstrates how to create foreign keys and indexes:
<code class="sql">CREATE TABLE customers ( customer_id INT PRIMARY KEY, customer_name VARCHAR(255) ); CREATE TABLE orders ( order_id INT PRIMARY KEY, customer_id INT, order_date DATE, FOREIGN KEY (customer_id) REFERENCES customers(customer_id) );</code>
In this example, MySQL will automatically create an index on the foreign key column orders.customer_id . But if you want to control the index more granularly, you can create the index manually, or choose the appropriate index type according to your actual situation. Remember, this is just a simple example. In actual application, you need to adjust it according to your specific situation. Don't forget to use EXPLAIN statement to analyze your query! This is the only way to become a database master!
The above is the detailed content of Whether mysql foreign key creates an index. 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)
The top 10 most authoritative cryptocurrency market websites in the world (the latest version of 2025)
Jul 29, 2025 pm 12:48 PM
The top ten authoritative cryptocurrency market and data analysis platforms in 2025 are: 1. CoinMarketCap, providing comprehensive market capitalization rankings and basic market data; 2. CoinGecko, providing multi-dimensional project evaluation with independence and trust scores; 3. TradingView, having the most professional K-line charts and technical analysis tools; 4. Binance market, providing the most direct real-time data as the largest exchange; 5. Ouyi market, highlighting key derivative indicators such as position volume and capital rate; 6. Glassnode, focusing on on-chain data such as active addresses and giant whale trends; 7. Messari, providing institutional-level research reports and strict standardized data; 8. CryptoCompa
What is Ethereum? What are the ways to obtain Ethereum ETH?
Jul 31, 2025 pm 11:00 PM
Ethereum is a decentralized application platform based on smart contracts, and its native token ETH can be obtained in a variety of ways. 1. Register an account through centralized platforms such as Binance and Ouyiok, complete KYC certification and purchase ETH with stablecoins; 2. Connect to digital storage through decentralized platforms, and directly exchange ETH with stablecoins or other tokens; 3. Participate in network pledge, and you can choose independent pledge (requires 32 ETH), liquid pledge services or one-click pledge on the centralized platform to obtain rewards; 4. Earn ETH by providing services to Web3 projects, completing tasks or obtaining airdrops. It is recommended that beginners start from mainstream centralized platforms, gradually transition to decentralized methods, and always attach importance to asset security and independent research, to
How to choose a free market website in the currency circle? The most comprehensive review in 2025
Jul 29, 2025 pm 06:36 PM
The most suitable tools for querying stablecoin markets in 2025 are: 1. Binance, with authoritative data and rich trading pairs, and integrated TradingView charts suitable for technical analysis; 2. Ouyi, with clear interface and strong functional integration, and supports one-stop operation of Web3 accounts and DeFi; 3. CoinMarketCap, with many currencies, and the stablecoin sector can view market value rankings and deans; 4. CoinGecko, with comprehensive data dimensions, provides trust scores and community activity indicators, and has a neutral position; 5. Huobi (HTX), with stable market conditions and friendly operations, suitable for mainstream asset inquiries; 6. Gate.io, with the fastest collection of new coins and niche currencies, and is the first choice for projects to explore potential; 7. Tra
Ethena treasury strategy: the rise of the third empire of stablecoin
Jul 30, 2025 pm 08:12 PM
The real use of battle royale in the dual currency system has not yet happened. Conclusion In August 2023, the MakerDAO ecological lending protocol Spark gave an annualized return of $DAI8%. Then Sun Chi entered in batches, investing a total of 230,000 $stETH, accounting for more than 15% of Spark's deposits, forcing MakerDAO to make an emergency proposal to lower the interest rate to 5%. MakerDAO's original intention was to "subsidize" the usage rate of $DAI, almost becoming Justin Sun's Solo Yield. July 2025, Ethe
Ethereum (ETH) NFT sold nearly $160 million in seven days, and lenders launched unsecured crypto loans with World ID
Jul 30, 2025 pm 10:06 PM
Table of Contents Crypto Market Panoramic Nugget Popular Token VINEVine (114.79%, Circular Market Value of US$144 million) ZORAZora (16.46%, Circular Market Value of US$290 million) NAVXNAVIProtocol (10.36%, Circular Market Value of US$35.7624 million) Alpha interprets the NFT sales on Ethereum chain in the past seven days, and CryptoPunks ranked first in the decentralized prover network Succinct launched the Succinct Foundation, which may be the token TGE
What is a stablecoin? Understand stablecoins in one article!
Jul 29, 2025 pm 01:03 PM
Stablecoins are cryptocurrencies with value anchored by fiat currency or commodities, designed to solve price fluctuations such as Bitcoin. Their importance is reflected in their role as a hedging tool, a medium of trading and a bridge connecting fiat currency with the crypto world. 1. The fiat-collateralized stablecoins are fully supported by fiat currencies such as the US dollar. The advantage is that the mechanism is simple and stable. The disadvantage is that they rely on the trust of centralized institutions. They represent the projects including USDT and USDC; 2. The cryptocurrency-collateralized stablecoins are issued through over-collateralized mainstream crypto assets. The advantages are decentralization and transparency. The disadvantage is that they face liquidation risks. The representative project is DAI. 3. The algorithmic stablecoins rely on the algorithm to adjust supply and demand to maintain price stability. The advantages are that they do not need to be collateral and have high capital efficiency. The disadvantage is that the mechanism is complex and the risk is high. There have been cases of dean-anchor collapse. They are still under investigation.
What is Binance Treehouse (TREE Coin)? Overview of the upcoming Treehouse project, analysis of token economy and future development
Jul 30, 2025 pm 10:03 PM
What is Treehouse(TREE)? How does Treehouse (TREE) work? Treehouse Products tETHDOR - Decentralized Quotation Rate GoNuts Points System Treehouse Highlights TREE Tokens and Token Economics Overview of the Third Quarter of 2025 Roadmap Development Team, Investors and Partners Treehouse Founding Team Investment Fund Partner Summary As DeFi continues to expand, the demand for fixed income products is growing, and its role is similar to the role of bonds in traditional financial markets. However, building on blockchain
Solana and the founders of Base Coin start a debate: the content on Zora has 'basic value'
Jul 30, 2025 pm 09:24 PM
A verbal battle about the value of "creator tokens" swept across the crypto social circle. Base and Solana's two major public chain helmsmans had a rare head-on confrontation, and a fierce debate around ZORA and Pump.fun instantly ignited the discussion craze on CryptoTwitter. Where did this gunpowder-filled confrontation come from? Let's find out. Controversy broke out: The fuse of Sterling Crispin's attack on Zora was DelComplex researcher Sterling Crispin publicly bombarded Zora on social platforms. Zora is a social protocol on the Base chain, focusing on tokenizing user homepage and content
