SELECT product_name, regist_date
  FROM Product
 WHERE regist_date > '2009-04-28';

View Code

/*
  下面是问题的SELECT语句
*/
-- ①
SELECT *
      FROM Product
     WHERE purchase_price = NULL;

-- ②
SELECT *
      FROM Product
     WHERE purchase_price <> NULL;

-- ③
SELECT *
      FROM Product
     WHERE product_name > NULL;

View Code

-- SELECT语句①
SELECT product_name, sale_price, purchase_price
  FROM Product
 WHERE sale_price >= purchase_price + 500;


-- SELECT语句②
SELECT product_name, sale_price, purchase_price
  FROM Product
 WHERE sale_price - 500 >= purchase_price;

SELECT product_name, product_type,
       sale_price * 0.9 - purchase_price AS profit
  FROM Product
 WHERE sale_price * 0.9 - purchase_price > 100
   AND (   product_type = '办公用品'
        OR product_type = '厨房用具');

View Code

=======================================

参考资料：

https://www.cnblogs.com/MarlonKang/p/12222429.html

end