在 SQL 中，WHERE 子句用于从表中选择满足指定条件的行，从而实现数据过滤。它通常与 SELECT、UPDATE、DELETE 等语句一起使用。
SELECT 列名
FROM 表名
WHERE 条件;
只有条件为 TRUE 的记录才会被返回。
SELECT * FROM employees
WHERE age > 30;
常用运算符：
= 等于<> 或 != 不等于> < >= <=SELECT * FROM employees
WHERE department = 'IT'
AND salary > 8000;
SELECT * FROM employees
WHERE department = 'IT'
OR department = 'HR';
SELECT * FROM products
WHERE price BETWEEN 100 AND 500;
SELECT * FROM employees
WHERE department IN ('IT', 'HR', 'Finance');
SELECT * FROM customers
WHERE name LIKE '张%';
%：任意字符（多个）_：任意一个字符SELECT * FROM orders
WHERE ship_date IS NULL;
SELECT * FROM employees
WHERE NOT department = 'IT';
⚠️ WHERE 不能直接用聚合函数（如 COUNT()、SUM()），需用 HAVING。
SELECT name, salary
FROM employees
WHERE department = 'IT'
AND salary BETWEEN 8000 AND 15000
AND name LIKE '李%';
如果你有具体数据库（MySQL / Oracle / SQL Server）或具体业务场景，我可以给你更针对性的写法。
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