/* create table inventory (
item varchar2(100),
color varchar2(100),
quantity number(10)
)*//*
insert into inventory values('table','blue',124);
insert into inventory values('table','red',223);
insert into inventory values('chair','blue',101);
insert into inventory values('chair','red',null);
insert into inventory values('chair','red',210); */
1、紅色商品的數量總和
select color, sum(nvl(quantity,0)) from inventory a where a.color='red' group by a.color;
2、按item分類，列出各類商品的數量
select item, sum(nvl(quantity,0)) from inventory a group by a.item;
3、按item分類，僅列出各類商品中紅色多於藍色的商品名稱及差額數量
select a.item, nvl(a.quantity,0)-nvl(b.quantity,0) from inventory a, inventory b
where nvl(a.quantity,0)>nvl(b.quantity,0) and a.color='red'
and b.color='blue' and a.item=b.item ;
4、按item分類，將資料按下列方式進行統計顯示
item red blue
select item , sum(nvl(red,0)) as red , sum(nvl(blue,0)) as blue from (select item,decode(color,'red',quantity,null) as red ,decode(color,'blue',quantity,null) as blue
from inventory) a
group by a.item order by item desc
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