How to add computed columns in SQL? Temporary calculation: Using the SELECT statement, there is no need to modify the table structure, and the calculation results only exist in the query results. Permanent save: Add new columns to the table, use the UPDATE statement to fill the data, and the calculation results are permanently saved in the table, but are not automatically updated. Usage views: Create virtual tables, encapsulate calculation results, easy to use, and does not occupy storage space.
SQL adds a computed column? Listen to me to tell you in detail
You ask how to add a calculated column in SQL? This question is very easy, but it actually has a secret. Many beginners think that is just adding a field and then calculating the calculation? naive! It depends on what your goal is, whether it is temporary calculation or permanent storage? This determines your approach.
Let’s talk about the basics first, you have to understand that the “columns” in SQL are not as casual as Excel tables. It is related to the table structure, and you must be cautious when changing it. Temporary calculations can be done with SELECT statements, and there is no need to change the table structure at all. For example, if you want to calculate the total price of each order, the order table has unit price and quantity, directly:
<code class="sql">SELECT order_id, price * quantity AS total_price FROM orders;</code>
This AS total_price gives the calculation result a name. The total_price column only exists in the query result this time, and the table itself has not changed. It's like a magic trick. It's like a trick, but it's gone in a blink of an eye. Convenient and fast, but the data is not lasting.
If you want to save the calculation results permanently, you have to be serious. You have to add a new column to the table and then use the UPDATE statement to fill in the data. For example, add a total_price column to the orders table:
<code class="sql">ALTER TABLE orders ADD COLUMN total_price DECIMAL(10, 2); -- 數(shù)據(jù)類型要選對(duì)！</code>
Then update the data:
<code class="sql">UPDATE orders SET total_price = price * quantity;</code>
This time total_price is added to the table, so it will be convenient to query in the future, and you don’t have to calculate it every time. but! Note that this is just a static snapshot. The unit price or quantity will change in the future, total_price will not be automatically updated. You have to regularly maintain it with UPDATE statements, or consider triggers to update it automatically. This is an advanced topic and depends on the support level of your database system.
There is a pit here, which is the selection of data types. DECIMAL(10, 2) is a random choice. You have to choose the appropriate data type according to the actual situation, otherwise it may overflow or the accuracy may be insufficient, resulting in an incorrect calculation result. This is not a joke, the data is wrong, and the consequences are very serious.
There is another more advanced way to play, which is to use views. A view can wrap the calculation results into a virtual table, which is like a real one, but it does not take up actual storage space. for example:
<code class="sql">CREATE VIEW order_with_total AS SELECT order_id, price, quantity, price * quantity AS total_price FROM orders;</code>
In the future, just use the order_with_total view to query, which is convenient and easy to save time. This method combines the advantages of temporary calculation and permanent storage, which is convenient for querying and does not increase the burden of table structure.
In short, there are many ways to add calculation columns in SQL, and which one should be chosen according to your actual needs. Don't be confused by the simplicity on the surface. Only by deeply understanding the concepts of data types, triggers, and views can you write efficient and reliable SQL code. Remember, the code is written for people to read and for machines to execute. Clear and efficient is the king. Only by practicing and thinking more can you become a true SQL master.
The above is the detailed content of How to add computed columns in SQL?. 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)
Ethereum shines: Bank of America starts digital asset tracking, ETH becomes the focus again
Aug 01, 2025 pm 08:09 PM
Bank of America starts digital asset tracking to mark the increase in Ethereum's recognition in mainstream finance. 1. Increase in legality recognition; 2. It may attract institutions to allocate digital assets; 3. Promote the compliance process; 4. Confirm the application prospects and potential value of ETH as a "digital oil"; Ethereum has become the focus because of its huge DApp ecosystem, 1. Upgrade technology to PoS to improve scalability, security and sustainability; 2. Support lending, trading and other financial services as the core of DeFi; 3. Support NFT prosperity and consolidate ecological demand; 4. Expand enterprise-level applications such as supply chain management; 5. EIP-1559 introduces a deflation mechanism to enhance scarcity; top trading platforms include: 1. Binance (trading volume)
Ouyi Exchange APP Android version v6.132.0 Ouyi APP official website download and installation guide 2025
Aug 04, 2025 pm 11:18 PM
OKX is a world-renowned comprehensive digital asset service platform, providing users with diversified products and services including spot, contracts, options, etc. With its smooth operation experience and powerful function integration, its official APP has become a common tool for many digital asset users.
The latest rankings of the top ten Bitcoin trading platforms in the world
Aug 01, 2025 pm 07:36 PM
1. Binance is a leading platform with global trading volume. It is known for its rich currency, diverse trading models and Launchpad financing services. It has a wide global layout; 2. OKX is famous for its innovative financial derivatives and high security, and actively deploys the Web3 ecosystem; 3.gate.io has a long history and provides more than 1,000 currency transactions, with stable systems and strict risk control; 4. Huobi provides diversified trading services, strong research strength, and pays attention to compliance and security; 5. KuCoin is known as the "national trading platform", attracting investors with low fees and high returns potential projects, and has fast customer service response; 6. Kraken is a well-known American exchange with strict security measures, supporting fiat currency transactions, and has high compliance; 7. Bitstamp is a veteran European platform, serving
Buy stablecoins, analyze all steps
Aug 01, 2025 pm 07:30 PM
The steps to purchase stablecoins are: 1. Choose a reputable trading platform, such as centralized exchanges such as Binance, Huobi, OKX, Coinbase, or decentralized exchanges such as Uniswap and PancakeSwap. You can also purchase them through the official website of the issuer of USDT, USDC, DAI, etc.; 2. Register an account and complete KYC identity verification, provide ID card or passport and other documents, and set up two-factor authentication (2FA) to enhance account security; 3. Bind a bank account or credit card, choose bank transfer, credit card payment or third-party payment and other methods to deposit fiat currency, and confirm the exchange rate and handling fee and complete recharge; 4. Enter the transaction interface to select "Filipino Transaction" or "Quick Buy Coin", and select the required stablecoin types such as
From blockchain to cryptocurrency, a complete analysis of basic concepts
Aug 06, 2025 pm 11:51 PM
Blockchain is a distributed and decentralized digital ledger technology. Its core principles include: 1. Distributed ledger ensures that data is stored simultaneously on all nodes; 2. Encryption technology, linking blocks through hash values to ensure that data is not tampered with; 3. Consensus mechanisms, such as PoW or PoS, ensure that transactions are agreed between nodes; 4. Decentralization, eliminating single point of control, enhancing censorship resistance; 5. Smart contracts, protocols for automated execution. Cryptocurrencies are digital assets issued based on blockchain. The operation process is: 1. The user initiates transactions and signs digitally; 2. The transactions are broadcast to the network; 3. The miner or verifier verifies the validity of the transaction; 4. Multiple transactions are packaged into new blocks; 5. Confirm the new zone through consensus mechanism
Blockchain browser: a must-have tool for querying digital currency transaction information
Aug 06, 2025 pm 11:27 PM
Blockchain browser is a necessary tool for querying digital currency transaction information. It provides a visual interface for blockchain data, so that users can query transaction hash, block height, address balance and other information; its working principle includes data synchronization, parsing, indexing and user interface display; core functions cover querying transaction details, block information, address balance, token data and network status; when using it, you need to obtain TxID and select the corresponding blockchain browser such as Etherscan or Blockchain.com to search; query address information to view balance and transaction history by entering the address; mainstream browsers include Bitcoin's Blockchain.com, Ethereum's Etherscan.io, B
Ethereum, a blockchain platform that surpasses Bitcoin, with advantages and innovation inventory
Aug 06, 2025 pm 11:57 PM
Through its Turing-complete smart contracts, EVM virtual machines and Gas mechanisms, Ethereum has built a programmable blockchain platform beyond Bitcoin, supporting diversified application ecosystems such as DeFi and NFT; its core advantages include a rich DApp ecosystem, strong programmability, active developer community and cross-chain interoperability; it is currently implementing consensus transformation from PoW to PoS through the upgrade of Ethereum 2.0, introducing beacon chains, verifier mechanisms and punishment systems to improve energy efficiency, security and decentralization; in the future, it will rely on sharding technology to realize data sharding and parallel processing, greatly improving throughput; at the same time, Rollup technology has been widely used as a Layer 2 solution, Optimistic Rollup and ZK-Rollu
What is the digital currency for ai smart sale? Where do ordinary people buy it?
Aug 01, 2025 pm 10:15 PM
AI digital currency is not an independent currency issued by AI, but a token that deeply integrates artificial intelligence technology into blockchain projects. Its value is closely related to the prospects of AI application. 1. AI is used for intelligent decision-making and optimization to improve DeFi efficiency; 2. Empower decentralized AI applications as a computing power payment and incentive tool; 3. Enhance network security and risk control to identify abnormal behaviors; 4. Combining AIGC and NFT, promote content generation and value flow. Ordinary people can participate through three channels: 1. Large centralized platforms (such as Binance and Ouyi), which are easy to operate and suitable for beginners; 2. Decentralized exchanges (such as Uniswap), which need to manage their own money and private keys, which have high security requirements; 3. Launchpad, which participates in the initial issuance platform (Launchpad).
