如何在MySQL中统计每周的唯一访问次数

CREATE TABLE access_logs (
    id INT AUTO_INCREMENT PRIMARY KEY,
    visitor_id VARCHAR(255),
    access_time DATETIME
);

INSERT INTO access_logs (visitor_id, access_time) VALUES ('visitor1', '2022-01-01 10:00:00');
INSERT INTO access_logs (visitor_id, access_time) VALUES ('visitor2', '2022-01-01 11:00:00');
INSERT INTO access_logs (visitor_id, access_time) VALUES ('visitor1', '2022-01-02 09:00:00');

SELECT WEEK(access_time) AS week, COUNT(DISTINCT visitor_id) AS unique_visitors
FROM access_logs
GROUP BY week;

SELECT WEEK(access_time) AS week, COUNT(DISTINCT visitor_id) AS unique_visitors
FROM access_logs
WHERE access_time >= '2022-01-01' AND access_time < '2023-01-01'
GROUP BY week;