联接已使您的结果集成倍增加，当您删除group by并使用*而不是指定的字段时，您将看到它。

select * from db.purchases t1 join db.searches
on t1.date = t2.date and t1.product = t2.product
where t1.date = '2017-01-01' and t1.product = 'Nike'

您不需要联接表来计算购买比率：

SELECT     
(select sum(t1.Total_sale) from db.purchases t1 where t1.date = '2017-01-01' and t1.product = 'Nike')
/
(select count(t2.Search_ID) from db.searches t2 where t2.date = '2017-01-01' and t2.product = 'Nike')

在联接之前进行聚合：

select p.product, p.sales, s.searches
from (select p.date, p.product, sum(p.Total_sale) as sales
      from db.purchases p
      group by p.date, p.product
     ) p join
     (select s.date, s.product, count(*) as searches
      from db.searches s
      group by s.date, s.product
     ) s
     on p.date = s.date and p.product = s.product
where p.date = '2017-01-01' and p.product = 'Nike';

注意：您可以移动 where 进入子查询，以提高性能。这将很容易推广到更多的日子和产品。

问题是您要连接两个未聚合的表，因此每个“购买”行都与每个“搜索”行相连接。所以你的结果是32994，它来自702x49。
使用连接实现所需结果的正确方法是

select  t1.product, t1.total_sales, t2.search_count
from    (
          select date, product, sum(total_sales) as total_sales
          from   db.purchases
          group by date, product
        ) t1
join    (
          select  date, product, count(search_id) as search_count
          from    db.searches
          group by date, product
        ) t2
on      t1.date = t2.date and t1.product = t2.product
where   t1.date = '2017-01-01' and t1.product = 'Nike'
group by t1.product, t1.date;