处理非常大的expand.grid？(Dealing with very large expand.grid?)

 您可以使用条件聚合简化事情： 
 
SELECT
    ThingName,
    count(ItemNumber) as TotalItems,
    count(case when ItemStatus='Red' then ItemNumber  end) as RedItems,
    count(case when ItemStatus='Blue' then ItemNumber  end) as BlueItems
FROM Things
GROUP BY ThingName;
 
 因此，不使用使用CASE表达式的子查询来获取Total，Red，Blue项的计数，而是直接在聚合函数内使用CASE表达式，在这种情况下为COUNT 。 
 
 在这里演示 

You can simplify things using conditional aggregation:
 
SELECT
    ThingName,
    count(ItemNumber) as TotalItems,
    count(case when ItemStatus='Red' then ItemNumber  end) as RedItems,
    count(case when ItemStatus='Blue' then ItemNumber  end) as BlueItems
FROM Things
GROUP BY ThingName;
 
Hence, instead of using a subquery that uses a CASE expression to get count of Total, Red, Blue items, use the CASE expression directly inside the aggregate function, COUNT in this case.
 
Demo here