提高 SQL 查询性能

Question

Sql:

select distinct DateAdd(Day, DateDiff(Day, 0, m.Receive_date), 0) as Date,
(select count(*) from Raw_Mats A where DateAdd(Day, DateDiff(Day, 0, A.Receive_date), 0)=DateAdd(Day, DateDiff(Day, 0, m.Receive_date), 0)) as Total,
(select count(*) from Raw_Mats B where DateAdd(Day, DateDiff(Day, 0, B.Receive_date), 0)=DateAdd(Day, DateDiff(Day, 0, m.Receive_date), 0) and B.status='Solved') as Delivered,
(select count(*) from Raw_Mats C where DateAdd(Day, DateDiff(Day, 0, C.Receive_date), 0)=DateAdd(Day, DateDiff(Day, 0, m.Receive_date), 0) and C.status='Pending') as UnDelivered
from Raw_Mats m where m.Receive_date between '2011-07-01' and '2011-07-21'

How to increase the performance of the above query. It is taking 44 secs. wanna make it less than 10 secs

Thanks

Answer 1

Do you have an index on both Receive_date and status ? (not an index on each, combined)

Also:

• You have have 4 touches in the table which means the query will scale at least O(4n). By using COUNT(CASE) you can remove Delivered and UnDelivered subqueries
• The simple count subquery isn't needed either
• You need GROUP BY. YOur DISTINCT is a work around for that
• BETWEEN is >= and <= which isn't the usually correct for dates with times

I've used a subquery here for clarity but it doesn't matter:

select
   DateOnly as Date,
   COUNT(*) AS Total,
   COUNT(CASE WHEN status='Solved' THEN 1 END) AS Delivered,
   COUNT(CASE WHEN status='Pending' THEN 1 END) AS UnDelivered
from
   (
   SELECT
       DateAdd(Day, DateDiff(Day, 0, m.Receive_date), 0) as DateOnly,
       status
   FROM
      Raw_Mats
   WHERE
      Receive_date >= '2011-07-01' AND Receive_date < '2011-07-21'
   ) T
 GROUP BY
   DateOnly

Edit, without subquery.

I started with a subquery because I thought it's be more complex than expected and didn't bother taking it out...

select
   DateAdd(Day, DateDiff(Day, 0, m.Receive_date), 0) as Date,
   COUNT(*) AS Total,
   COUNT(CASE WHEN status='Solved' THEN 1 END) AS Delivered,
   COUNT(CASE WHEN status='Pending' THEN 1 END) AS UnDelivered
from
   Raw_Mats
WHERE
   Receive_date >= '2011-07-01' AND Receive_date < '2011-07-21'
GROUP BY
   DateAdd(Day, DateDiff(Day, 0, m.Receive_date), 0)

Answer 2

Divide and conquer: Just try each part of your sql as a separate statement and you'll find out which part is slow. If you have sub-selects and functions there is a good chance, that the server need temp-tables to perform the select, if you haven't got enough memory (or a large dataset or configured your sql server to do so), this temp-objects are swapped to disk, which makes it slow too.

Answer 3

Too many sub queries man. Get rid of some of them and it will help. Also you should not use functions on both sides in your sqls.

For example:

where DateAdd(Day, DateDiff(Day, 0, A.Receive_date), 0)=
              DateAdd(Day, DateDiff(Day, 0, m.Receive_date), 0) 

In this specific case the db engine will have to go through all the rows to evaluate DateDiff(Day, 0, A.Receive_date) and DateAdd(Day, DateDiff(Day, 0, A.Receive_date), 0) then compare it with the right hand side which also is a function. This simply is a disaster.

Also, do you have indexes on Receive_date ? If not add it.