MySQL การใช้งานฟังก์ชัน DAYOFWEEK()

SELECT DAYOFWEEK('2025-04-10') AS weekday_number;
-- ผลลัพธ์: 5 (คือ Thursday)

SELECT DAYOFWEEK(NOW()) AS today_day_index;

SELECT *
FROM orders
WHERE DAYOFWEEK(order_date) IN (1, 7); -- 1=Sunday, 7=Saturday

SELECT DAYOFWEEK(order_date) AS weekday_number, COUNT(*) AS total_orders
FROM orders
GROUP BY DAYOFWEEK(order_date)
ORDER BY weekday_number;

SELECT 
  order_date,
  CASE DAYOFWEEK(order_date)
    WHEN 1 THEN 'Sunday'
    WHEN 2 THEN 'Monday'
    WHEN 3 THEN 'Tuesday'
    WHEN 4 THEN 'Wednesday'
    WHEN 5 THEN 'Thursday'
    WHEN 6 THEN 'Friday'
    WHEN 7 THEN 'Saturday'
  END AS weekday_name
FROM orders;