MySQL common function operations: optimize query and data processing

In database development, functions are a powerful tool that can be used for query optimization, data manipulation, and data transformation. As a popular relational database, MySQL provides a wealth of built-in functions for handling various database operations. This article will give an in-depth introduction to the common function operations of MySQL to help you optimize queries and process data.

1. Aggregation function

COUNT function: used to count the number of records.

SELECT COUNT(*) FROM orders;

SUM function: used for summing.

SELECT SUM(price) FROM products;

AVG function: used to calculate the average value.

SELECT AVG(age) FROM employees;

MAX and MIN functions: used to find the maximum and minimum values ​​respectively.

SELECT MAX(salary) FROM employees;
SELECT MIN(salary) FROM employees;

2. String functions

CONCAT function: used to concatenate multiple strings.

SELECT CONCAT(first_name, ' ', last_name) AS full_name FROM users;

LENGTH function: used to calculate the length of a string.

SELECT LENGTH(description) FROM products;

UPPER and LOWER functions: used to convert to uppercase and lowercase respectively.

SELECT UPPER(username) FROM users;
SELECT LOWER(email) FROM users;

SUBSTRING function: used to intercept substrings.

SELECT SUBSTRING(title, 1, 10) FROM articles;

3. Date function

NOW function: returns the current date and time.

SELECT NOW();

DATE_FORMAT function: used to format the date.

SELECT DATE_FORMAT(order_date, '%Y-%m-%d') FROM orders;

DATEDIFF function: Used to calculate the difference in days between two dates.

SELECT DATEDIFF('2023-07-01', '2023-06-15');

4. Conditional function

IF function: Returns different values ​​based on conditions.

SELECT IF(quantity > 10, 'In Stock', 'Out of Stock') FROM products;

CASE function: perform multi-branch judgment according to conditions.

SELECT 
    CASE 
        WHEN age < 18 THEN 'Minor'
        WHEN age >= 18 AND age < 65 THEN 'Adult'
        ELSE 'Senior' 
    END AS age_group 
FROM persons;

Five, type conversion function

CAST function: perform data type conversion.

SELECT CAST(price AS DECIMAL(10, 2)) FROM products;

CONVERT function: It is also used for data type conversion, but it may be used differently in different database systems.

SELECT CONVERT(price, DECIMAL(10, 2)) FROM products;

6. Grouping function

GROUP_CONCAT function: Concatenates a set of values ​​into a string.

SELECT department, GROUP_CONCAT(name) FROM employees GROUP BY department;

Combination of GROUP BY and aggregate function: used for grouping and aggregate calculation.

SELECT department, AVG(salary) FROM employees GROUP BY department;

---

MySQL's built-in functions provide powerful tools for query optimization and data manipulation. From aggregate functions, string functions, date functions to conditional functions and type conversion functions, each function has a specific purpose and function. Mastering these commonly used functions can improve efficiency in database development, reduce the amount of code, and better process and convert data. Through in-depth understanding and practice, you can flexibly use these functions in data operations, and write efficient and elegant database query and processing codes.