The AVG function in SQL is used to calculate the average of numeric values. Its syntax is AVG(column_name). AVG functions ignore NULL values. You can use the AS keyword to specify aliases for results. It only works for numeric type data, returning NULL if the target column has no value or contains only NULL values, and throwing an error if it contains non-numeric values.
Usage of AVG function in SQL
The AVG function in SQL is used to calculate the value of a set of numeric values average value.
Syntax:
<code>AVG(column_name)</code>
Where:
-
column_name
is the target column to calculate the average.
Usage:
<code>-- 示例表包含 'sales' 列,存储销售数据 CREATE TABLE sales ( product_id INT, sales INT ); -- 计算 'sales' 列的平均值 SELECT AVG(sales) FROM sales;</code>
Return result:
<code>NULL</code>
Because there is no data in the table yet, the result is NULL.
Handling NULL values:
AVG functions ignore NULL values. For example:
<code>-- 在 'sales' 列中插入一些数据,包括 NULL 值 INSERT INTO sales (product_id, sales) VALUES (1, 10), (2, 20), (3, NULL); -- 计算 'sales' 列的平均值 SELECT AVG(sales) FROM sales;</code>
Returns:
<code>15.0</code>
The AVG function ignores NULL values, so the average is (10 20) / 2 = 15.
Using aliases:
You can use the AS
keyword to specify an alias for the result of an AVG function. For example:
<code>-- 计算 'sales' 列的平均值并将其别名为 'average_sales' SELECT AVG(sales) AS average_sales FROM sales;</code>
Return result:
<code>| average_sales | |---|---| | 15.0 |</code>
Note:
- AVG function only applies to numeric types The data.
- If the target column has no values or contains only NULL values, the AVG function returns NULL.
- The AVG function throws an error if the target column contains non-numeric values.
The above is the detailed content of Usage of avg function in sql. For more information, please follow other related articles on the PHP Chinese website!

SQL is a language used to manage and operate relational databases. 1. Create a table: Use CREATETABLE statements, such as CREATETABLEusers(idINTPRIMARYKEY, nameVARCHAR(100), emailVARCHAR(100)); 2. Insert, update, and delete data: Use INSERTINTO, UPDATE, DELETE statements, such as INSERTINTOusers(id, name, email)VALUES(1,'JohnDoe','john@example.com'); 3. Query data: Use SELECT statements, such as SELEC

The relationship between SQL and MySQL is: SQL is a language used to manage and operate databases, while MySQL is a database management system that supports SQL. 1.SQL allows CRUD operations and advanced queries of data. 2.MySQL provides indexing, transactions and locking mechanisms to improve performance and security. 3. Optimizing MySQL performance requires attention to query optimization, database design and monitoring and maintenance.

SQL is used for database management and data operations, and its core functions include CRUD operations, complex queries and optimization strategies. 1) CRUD operation: Use INSERTINTO to create data, SELECT reads data, UPDATE updates data, and DELETE deletes data. 2) Complex query: Process complex data through GROUPBY and HAVING clauses. 3) Optimization strategy: Use indexes, avoid full table scanning, optimize JOIN operations and paging queries to improve performance.

SQL is suitable for beginners because it is simple in syntax, powerful in function, and widely used in database systems. 1.SQL is used to manage relational databases and organize data through tables. 2. Basic operations include creating, inserting, querying, updating and deleting data. 3. Advanced usage such as JOIN, subquery and window functions enhance data analysis capabilities. 4. Common errors include syntax, logic and performance issues, which can be solved through inspection and optimization. 5. Performance optimization suggestions include using indexes, avoiding SELECT*, using EXPLAIN to analyze queries, normalizing databases, and improving code readability.

In practical applications, SQL is mainly used for data query and analysis, data integration and reporting, data cleaning and preprocessing, advanced usage and optimization, as well as handling complex queries and avoiding common errors. 1) Data query and analysis can be used to find the most sales product; 2) Data integration and reporting generate customer purchase reports through JOIN operations; 3) Data cleaning and preprocessing can delete abnormal age records; 4) Advanced usage and optimization include using window functions and creating indexes; 5) CTE and JOIN can be used to handle complex queries to avoid common errors such as SQL injection.

SQL is a standard language for managing relational databases, while MySQL is a specific database management system. SQL provides a unified syntax and is suitable for a variety of databases; MySQL is lightweight and open source, with stable performance but has bottlenecks in big data processing.

The SQL learning curve is steep, but it can be mastered through practice and understanding the core concepts. 1. Basic operations include SELECT, INSERT, UPDATE, DELETE. 2. Query execution is divided into three steps: analysis, optimization and execution. 3. Basic usage is such as querying employee information, and advanced usage is such as using JOIN connection table. 4. Common errors include not using alias and SQL injection, and parameterized query is required to prevent it. 5. Performance optimization is achieved by selecting necessary columns and maintaining code readability.

SQL commands are divided into five categories in MySQL: DQL, DDL, DML, DCL and TCL, and are used to define, operate and control database data. MySQL processes SQL commands through lexical analysis, syntax analysis, optimization and execution, and uses index and query optimizers to improve performance. Examples of usage include SELECT for data queries and JOIN for multi-table operations. Common errors include syntax, logic, and performance issues, and optimization strategies include using indexes, optimizing queries, and choosing the right storage engine.


Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

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

Atom editor mac version download
The most popular open source editor

SublimeText3 English version
Recommended: Win version, supports code prompts!

mPDF
mPDF is a PHP library that can generate PDF files from UTF-8 encoded HTML. The original author, Ian Back, wrote mPDF to output PDF files "on the fly" from his website and handle different languages. It is slower than original scripts like HTML2FPDF and produces larger files when using Unicode fonts, but supports CSS styles etc. and has a lot of enhancements. Supports almost all languages, including RTL (Arabic and Hebrew) and CJK (Chinese, Japanese and Korean). Supports nested block-level elements (such as P, DIV),

DVWA
Damn Vulnerable Web App (DVWA) is a PHP/MySQL web application that is very vulnerable. Its main goals are to be an aid for security professionals to test their skills and tools in a legal environment, to help web developers better understand the process of securing web applications, and to help teachers/students teach/learn in a classroom environment Web application security. The goal of DVWA is to practice some of the most common web vulnerabilities through a simple and straightforward interface, with varying degrees of difficulty. Please note that this software

MinGW - Minimalist GNU for Windows
This project is in the process of being migrated to osdn.net/projects/mingw, you can continue to follow us there. MinGW: A native Windows port of the GNU Compiler Collection (GCC), freely distributable import libraries and header files for building native Windows applications; includes extensions to the MSVC runtime to support C99 functionality. All MinGW software can run on 64-bit Windows platforms.