I am in need of resetting flag of a table 'A'
from 'X'
to 'Y'
where the update_date of a row satisfies the conditions 1. update_date > 1 month, 2. flag = 'X' & 3. type = 1
.
And the update_date is checked against another table 'B'
. I hope the following query will explain what exactly I need. Also this query works fine for me. But the problem is it is taking too long time. Actually my tables A & B
are much bigger almost contains billion rows and there are about 10 columns.
When I run my sub query for selecting A.id
I got the result immediately.
SELECT a.id
FROM A a
JOIN B b
ON (a.id = b.id
AND a.name = b.name
AND a.type = 1
AND a.flag = 'X'
AND a.update_date > DATE_SUB(NOW(), INTERVAL 1 MONTH) tmp_table)
But only the update query even if I put limit also it's taking much time.
UPDATE A
SET flag='Y'
WHERE id IN (SELECT a.id
FROM A a
JOIN B b
ON (a.id = b.id
AND a.name = b.name
AND a.type = 1
AND a.flag = 'X'
AND a.update_date > DATE_SUB(NOW(), INTERVAL 1 MONTH) tmp_table))
LIMIT 100
I am looking for alternate solutions of my query which makes it fast. Hope I could write a stored procedure for it. But in SP
I should loop through for each target_ids right?
I don't wish to write two separate queries in PHP, since there are many threads of my PHP scripts running on cron which returns same results (time latency).
Also to note, I do have enough indexing for columns.
Wish to update limits by limit. ie., update 1000+ records for every run.
Change in with exists
EXISTS will be faster because once the engine has found a hit, it will quit looking as the condition has proved true. With IN it will collect all the results from the subquery before further processing.
UPDATE A a
JOIN B b
ON (a.id = b.id
AND a.name = b.name
AND a.type = 1
AND a.flag = 'X'
AND a.update_date > DATE_SUB(NOW(), INTERVAL 1 MONTH))
SET a.flag='Y'
ORDER BY a.id LIMIT 1000;
EDITED Supporting substitute of LIMIT (IT will update only 1st 100 records)
SET @rn = 0;
UPDATE A a
JOIN (SELECT @rn:=@rn+1 AS rId, id, name FROM B b
JOIN A a
ON (@rn < 100 AND a.id = b.id
AND a.name = b.name
AND a.type = 1
AND a.flag = 'X'
AND a.update_date > DATE_SUB(NOW(), INTERVAL 1 MONTH)
)
) b
ON (a.id=b.id)
SET a.flag='Y'
WHERE b.rId < 100;
Using exist clause
Update A a
SET a.flag='Y'
WHERE EXISTS (SELECT 1 FROM B b WHERE a.id = b.id
AND a.name = b.name
AND a.type = 1
AND a.flag = 'X'
AND a.update_date > DATE_SUB(NOW(), INTERVAL 1 MONTH))
ORDER BY a.id LIMIT 1000;
Hope this helps
You can use a join too
UPDATE A
LEFT JOIN (SELECT
a.id
FROM A AS a
JOIN B AS b
ON a.id = b.id
WHERE a.name = b.name
AND a.type = 1
AND a.flag = 'X'
AND a.update_date > DATE_SUB(NOW(), INTERVAL 1 MONTH)) AS l
ON l.id = A.id
SET flag = 'Y'
WHERE id = l.id
Finally, I got the better performing optimized query. Simply A join to temp table.
UPDATE A AS a JOIN (
SELECT a.id FROM A AS a JOIN B AS b ON
b.type = a.type
AND b.name = a.name
AND b.last_update_date < DATE_SUB(NOW(), INTERVAL 1 MONTH)
AND a.type = 1
AND a.flag = 'X'
ORDER BY a.id DESC LIMIT 1000)
AS source ON source.id = a.id
SET flag = 'Y';
Thanks to http://www.xaprb.com/blog/2006/08/10/how-to-use-order-by-and-limit-on-multi-table-updates-in-mysql
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.