Choone three
Examine the description of the PRODUCTS table:
Name Null? Type
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PRODUCT_ID NOT NULL NUMBER(2)
PRODUCT_NANE VARCHAR2(10)
UNIT_PRICE NUMBER(3)
PURCHARGE VARCHAR2(2)
EXPIRY_DATE DATE
DELIVERY_DATE DATE
Which three queres use valid expressions?
A) SELECT produet_id, unit_pricer, 5 "Discount",unit_price+purcharge-discount FROM products;
B) SELECT product_id, (unit_price * 0.15 / (4.75 + 552.25)) FROM products;
C) SELECT ptoduct_id, (expiry_date - delivery_date) * 2 FROM products;
D) SPLECT product_id, expiry_date * 2 FROM products;
E) SELEGT product_id, unit_price, unit_price + Purcharge FROM products;
F) SELECT product_id,unit_price || "Discount" , unit_price + surcharge - discount FROM products;
Answer：BCE
(解析：如果字符型的存储的是数字，那么查询的时候 oracle 会自动转化，否则会转化失败;
A 的 Answer：5 "Discount"就是添加一个新列，值为 5，但是虚拟的列不能放在数学表达式中。
Answer：F 中不能是双引号，字符串要用单引号，别名用双引号。)