从理论到实践详解MySQL中的连表查询和更新

UPDATE table1 t1
JOIN table2 t2 ON t1.common_field = t2.common_field
SET t1.field1 = t2.field2,
    t1.field3 = t2.field4
WHERE [condition];

UPDATE table1 t1, table2 t2
SET t1.field1 = t2.field2
WHERE t1.common_field = t2.common_field
AND [other_conditions];

UPDATE employees e
JOIN departments d ON e.dept_id = d.dept_id
SET e.dept_name = d.dept_name;

UPDATE research_report_file t1
LEFT JOIN research_report t2 ON t1.data_id = t2.id
SET 
    t1.file_name = t2.report_name,
    t1.file_type = t2.file_type
WHERE 
    t1.file_name IS NULL;

UPDATE orders o
JOIN customers c ON o.customer_id = c.id
JOIN regions r ON c.region_id = r.id
SET o.region_name = r.name,
    o.discount_rate = CASE 
        WHEN c.membership_level = 'gold' THEN 0.2
        WHEN c.membership_level = 'silver' THEN 0.1
        ELSE 0
    END
WHERE o.status = 'pending';

UPDATE table1 t1
SET t1.field1 = (
    SELECT t2.field2 
    FROM table2 t2 
    WHERE t2.id = t1.related_id
)
WHERE EXISTS (
    SELECT 1 FROM table2 t2 
    WHERE t2.id = t1.related_id
);

UPDATE products p
JOIN categories c ON p.category_id = c.id
SET 
    p.price = CASE 
        WHEN c.name = 'Electronics' THEN p.price * 1.1
        WHEN c.name = 'Clothing' THEN p.price * 0.9
        ELSE p.price
    END,
    p.updated_at = NOW()
WHERE p.status = 'active';

UPDATE main_table m
LEFT JOIN related_table r ON m.id = r.main_id
SET m.related_value = IFNULL(r.value, 'default'),
    m.last_updated = NOW()
WHERE m.status = 'pending';