UPDATE 表1
[JOIN 子句]  -- 可以包含多個(gè)JOIN
SET 表1.列1 = 表達(dá)式1, 
    表1.列2 = 表達(dá)式2,
    ...
[WHERE 條件];

UPDATE orders o
JOIN customers c ON o.customer_id = c.customer_id
SET o.discount = 0.1
WHERE c.vip_level = 'Gold';

UPDATE products p
LEFT JOIN inventory i ON p.product_id = i.product_id
SET p.status = CASE 
    WHEN i.quantity <= 0 THEN 'Out of Stock'
    WHEN i.quantity < 5 THEN 'Low Stock'
    ELSE 'In Stock'
END;

UPDATE order_details od
JOIN orders o ON od.order_id = o.order_id
JOIN products p ON od.product_id = p.product_id
SET od.unit_price = p.standard_price * 0.9
WHERE o.order_date < '2023-01-01';

UPDATE products p
SET p.price = (
    SELECT AVG(od.unit_price) 
    FROM order_details od 
    JOIN orders o ON od.order_id = o.order_id
    WHERE od.product_id = p.product_id 
    AND o.order_date > DATE_SUB(NOW(), INTERVAL 1 YEAR)
)
WHERE EXISTS (
    SELECT 1 
    FROM order_details od 
    WHERE od.product_id = p.product_id
);

UPDATE employees e
JOIN departments d ON e.dept_id = d.dept_id
JOIN locations l ON d.location_id = l.location_id
SET e.salary = CASE 
    WHEN l.region = 'North' AND d.name = 'Engineering' THEN e.salary * 1.1
    WHEN l.region = 'South' THEN e.salary * 1.05
    ELSE e.salary * 1.03
END;

UPDATE employees e1
JOIN employees e2 ON e1.manager_id = e2.employee_id
SET e1.department = e2.department
WHERE e2.department = 'Marketing';

-- 為常用JOIN條件添加索引
ALTER TABLE orders ADD INDEX idx_customer_id (customer_id);
ALTER TABLE customers ADD INDEX idx_vip_level (vip_level);

-- 第一次更新
UPDATE products p
JOIN inventory i ON p.product_id = i.product_id
SET p.last_updated = NOW()
WHERE p.product_id BETWEEN 1 AND 1000
AND i.quantity < 10;

-- 第二次更新
UPDATE products p
JOIN inventory i ON p.product_id = i.product_id
SET p.last_updated = NOW()
WHERE p.product_id BETWEEN 1001 AND 2000
AND i.quantity < 10;

EXPLAIN UPDATE orders o
JOIN customers c ON o.customer_id = c.customer_id
SET o.status = 'Processed'
WHERE c.country = 'China';

-- 將參與促銷(xiāo)的商品價(jià)格更新為促銷(xiāo)價(jià)
UPDATE products p
JOIN promotions pr ON p.product_id = pr.product_id
JOIN promo_categories pc ON pr.category_id = pc.category_id
SET p.current_price = pr.promo_price,
    p.last_price_update = NOW()
WHERE pc.promo_name = 'Summer Sale'
AND pr.start_date <= NOW()
AND pr.end_date >= NOW();

-- 根據(jù)績(jī)效和部門(mén)調(diào)整薪資
UPDATE employees e
JOIN departments d ON e.dept_id = d.dept_id
JOIN performance_reviews pr ON e.employee_id = pr.employee_id
SET e.salary = CASE 
    WHEN pr.rating >= 4.5 AND d.name IN ('Sales', 'Engineering') 
        THEN e.salary * 1.15
    WHEN pr.rating >= 3.5 
        THEN e.salary * 1.08
    ELSE e.salary * 1.03
END,
e.last_salary_review = NOW()
WHERE pr.review_date = (SELECT MAX(review_date) FROM performance_reviews pr2 
                       WHERE pr2.employee_id = e.employee_id);

-- 根據(jù)采購(gòu)訂單更新庫(kù)存
UPDATE inventory i
JOIN purchase_orders po ON i.product_id = po.product_id
JOIN po_items poi ON po.order_id = poi.order_id AND i.product_id = poi.product_id
SET i.quantity = i.quantity + poi.quantity_received,
    i.last_updated = NOW()
WHERE po.status = 'Completed'
AND poi.quantity_received > 0;