如何处理大型mysql查询

Question

i have the following query:

SELECT  p2c.pid AS productNumber,
        p.name AS productName
    ,   (
            SELECT COUNT(*)
            FROM   products2customers
            WHERE  pid = p2c.pid
        ) AS registered
    ,   (
            SELECT COUNT(*)
            FROM   products2customers
            WHERE  pid = p2c.pid
               AND date_add(from_unixtime(purchased), INTERVAL 5 YEAR) >= CURDATE()
        ) AS inWarranty
    ,   (
            SELECT COUNT(*)
            FROM   products2customers
            WHERE  pid = p2c.pid
               AND date_add(from_unixtime(purchased), INTERVAL 5 YEAR) < CURDATE()
        ) AS outOfWarranty
    ,   (
            SELECT DATE_FORMAT( MAX( from_unixtime(purchased) ), '%d.%m.%Y')
            FROM   products2customers
            WHERE  pid = p2c.pid
        ) AS lastPurchased
    ,   (
            SELECT DATE_FORMAT( date_add( MAX( from_unixtime(purchased) ), INTERVAL 5 YEAR), '%d.%m.%Y')
            FROM   products2customers
            WHERE  pid = p2c.pid
        ) AS warrantyUntil
FROM    (
            SELECT DISTINCT
                p2c.pid
            FROM
                products2customers p2c
        ) AS p2c
JOIN
    products p
ON
    p.id = p2c.pid
ORDER BY
    inWarranty DESC

The query is executed on a database table, which has 25.000 rows. The execution time for this query is at about 40 secs. The results will be shown at a webpage, so it's not so great to wait 40secs for the result.

Is there a way, to execute this query and save it's output? Because it would be enough if this query is executed every night.

What's the best way for doing this? Should I create a cronjob and execute this query and write the result in a database? Or is there a better way?

Or can i optimize this query, to make it faster?

Answer 1

I think all those correlated subqueries are killing you. Try this:

SELECT  p2c.pid AS productNumber,
        p.name AS productName,
        COUNT(*) AS registered,
        SUM(date_add(from_unixtime(purchased), INTERVAL 5 YEAR) >= CURDATE()) AS inWarranty,
        SUM(date_add(from_unixtime(purchased), INTERVAL 5 YEAR) < CURDATE()) AS outOfWarranty,
        DATE_FORMAT( MAX( from_unixtime(purchased) ), '%d.%m.%Y') AS lastPurchased,
        DATE_FORMAT( date_add( MAX( from_unixtime(purchased) ), INTERVAL 5 YEAR), '%d.%m.%Y') AS warrantyUntil
FROM products2customers p2c
JOIN products p ON p.id = p2c.pid
GROUP BY p2c.pid
ORDER BY inWarranty DESC

Answer 2

也许首先要Explain Plan一个Explain Plan ，看看是否可以通过创建索引来加速任何部分。

Answer 3

Put this into a cron job:

CREATE TABLE products_warrany SELECT p2c.pid AS productNumber, ...

Later use the following query instead of original long one:

SELECT * FROM products_warrany ORDER BY ...

You also gain ability to run additional filtering, ordering and so forth. Reference.