mysql 语句表示空

INSERT INTO table_name (column1, column2) VALUES ('value1', NULL);

SELECT * FROM table_name WHERE column_name IS NULL;

SELECT column1, IFNULL(column2, 'default_value') AS column2 FROM table_name;

-- 创建一个包含可选字段的表
CREATE TABLE users (
    id INT PRIMARY KEY,
    name VARCHAR(255) NOT NULL,
    middle_name VARCHAR(255) -- 允许NULL值
);

-- 插入数据，其中middle_name为NULL
INSERT INTO users (id, name, middle_name) VALUES (1, 'John Doe', NULL);

-- 查询包含NULL值的记录
SELECT * FROM users WHERE middle_name IS NULL;

-- 避免在查询结果中出现NULL值
SELECT id, name, IFNULL(middle_name, 'N/A') AS middle_name FROM users;