SQL中如何用CASE结合不等于条件 CASE语句中的条件判断

CASE
    WHEN column1 <> value1 THEN result1
    WHEN column2 != value2 THEN result2
    ELSE default_result
END

CASE
    WHEN column1 IS NULL THEN 'Column1 is NULL'
    WHEN column1 IS NOT NULL AND column1 <> 'some_value' THEN 'Column1 is not NULL and not equal to some_value'
    ELSE 'Column1 is not NULL and equal to some_value'
END

CASE
    WHEN column2 = '' THEN 'Column2 is an empty string'
    WHEN column2 <> '' THEN 'Column2 is not an empty string'
    ELSE 'Column2 is something else (possibly NULL, depends on your database)'
END

UPDATE your_table
SET column_to_update =
    CASE
        WHEN condition1 <> value1 THEN new_value1
        WHEN condition2 != value2 THEN new_value2
        ELSE column_to_update  -- 保持原值
    END
WHERE some_other_condition; -- 可选的WHERE子句

-- 避免这样写
SELECT *
FROM your_table
WHERE
    CASE
        WHEN column1 > 10 THEN column2
        ELSE column3
    END <> 'some_value';

-- 尽量简化条件，或者使用其他方式重写查询

UPDATE orders
SET shipping_status =
    CASE
        WHEN order_status = 'pending' AND payment_status <> 'paid' THEN 'awaiting_payment'
        WHEN order_status = 'processing' AND inventory_status != 'available' THEN 'awaiting_inventory'
        WHEN order_status = 'shipped' AND tracking_number IS NULL THEN 'tracking_error'
        ELSE shipping_status -- 保持原状态
    END
WHERE order_date < CURRENT_DATE - INTERVAL '7 day'; -- 只更新7天前的订单