ADV米粮包里面有这样一道题:
Q: left join and in-line view
Product
Product_id Product
1 1001
2 1002
3 1003
Sales
Product_id Sales
3 100
1 200
5 100
1 200
3 100
1 100
Proc sql;
Select p.product s.totalsales
From product as p
left join (select sum(sales) as totalsales from sales as s)
on p.product_id=s.product_id;
quit;
What is the output?
Answer:
Product Totalsales
1001 500
1002 .
1003 200
这里我有点不解的地方是,left join后面的语句中,sum(sales)是group之后每一种类型product的总和呢,还是没有group的总和?看答案是已经group好每一种Product的toatal sales了,我想知道是在哪里进行了这个group的操作呢?是下一行的on p.product_id=s.product_id这里吗?(我以为on语句这里只是对left join起作用的)