索引法则--少用OR，它在连接时会索引失效

DROP TABLE IF EXISTS staff;
CREATE TABLE IF NOT EXISTS staff (
    id INT PRIMARY KEY auto_increment,
    name VARCHAR(50),
    age INT,
    pos VARCHAR(50) COMMENT ‘职位‘,
    salary DECIMAL(10,2)
);

INSERT INTO staff(name, age, pos, salary) VALUES(‘Alice‘, 22, ‘HR‘, 5000);

CREATE INDEX idx_nameAgePos ON staff(name, age, pos);

EXPLAIN SELECT * FROM staff WHERE name = ‘Alice‘ or name = ‘Bob‘;