mysql处理函数

SELECT CONCAT('Hello', ' ', 'World') AS greeting;
SELECT SUBSTRING('Hello World', 1, 5) AS sub_str;

SELECT SUM(salary) AS total_salary FROM employees;
SELECT AVG(age) AS average_age FROM users;

SELECT NOW() AS current_time;
SELECT DATE_ADD('2023-01-01', INTERVAL 1 DAY) AS next_day;

SELECT COUNT(*) AS total_records FROM products;
SELECT GROUP_CONCAT(name SEPARATOR ', ') AS product_names FROM categories;

SELECT IF(age > 18, 'Adult', 'Minor') AS age_group FROM users;
SELECT CASE WHEN salary > 5000 THEN 'High' ELSE 'Low' END AS salary_level FROM employees;

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

SELECT IFNULL(column_name, 'default_value') AS processed_column FROM table_name;
SELECT COALESCE(column_name, 'default_value') AS processed_column FROM table_name;