UPDATE MySQL Query taking a long time to execute - ways to optimize - mysql

Question

I have a doubt with the following query.
update src_woz_waardeklasse_2011 a use index(waardeklasse_main,woz_val)
inner join waardeklasse_average b use index (waardeklasse)
on b.waardeklasse_new = a.waardeklasse
set a.woz_value = b.average
where b.waardeklasse_new = a.waardeklasse;
I am trying to update a new column 'woz_val' in the 'src_woz_waardeklasse_2011' table using the 'average' values from the 'waardeklasse_average' table. I am joining using the 'waaderklasse' numbers in both the tables. But the 'src_woz_waardeklasse_2011' table is nearly 7 million records and the 'waardeklasee_average' table is 46 records. So the query is taking a really long time. 25 minutes and counting.
Is there a way to optimize it? I am sure it's taking a long time as I am trying to compare values between a large table and a small table. I have included the table structure of both the tables below.
src_woz_waardeklasse_2011
+----------------------+---------------------------+------+-----+---------+-
---------------+
| Field | Type | Null | Key | Default |
Extra |
+----------------------+---------------------------+------+-----+---------+-
---------------+
| id | int(11) unsigned | NO | PRI | NULL |
auto_increment |
| postcode | varchar(150) | YES | MUL | NULL |
|
| huisnummeraanduiding | varchar(150) | YES | | NULL |
|
| huisletter | varchar(150) | YES | | NULL |
|
soort_woonobject | varchar(150) | YES | | NULL |
|
| bouwjaar | varchar(150) | YES | | NULL |
|
| bouwjaarsklasse | varchar(150) | YES | | NULL |
|
| inhoud | varchar(150) | YES | | NULL |
|
| reg_oppervlak | varchar(150) | YES | | NULL |
|
| woz_value | int(15) unsigned zerofill | YES | UNI | NULL |
|
| reg_oppervlak_bn | varchar(150) | YES | | NULL |
|
| waardeklasse | int(10) | NO | PRI | NULL |
|
| waardepeildatum | varchar(150) | YES | | NULL |
|
| zipandnumber | varchar(150) | YES | | NULL |
|
+----------------------+---------------------------+------+-----+---------+-
---------------+
waardeklasse_average
+-------------------------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------------------------+---------+------+-----+---------+-------+
| waardeklasse_average_id | int(11) | NO | | NULL | |
| waardeklasse_new | int(10) | NO | PRI | NULL | |
| lower | int(11) | NO | | NULL | |
| higher | int(11) | NO | | NULL | |
| average | int(11) | NO | PRI | NULL | |
+-------------------------+---------+------+-----+---------+-------+

Answer 1

update src_woz_waardeklasse_2011 a use index(waardeklasse_main,woz_val)
Left join waardeklasse_average b
on b.waardeklasse_new = a.waardeklasse
set a.woz_value = b.average
where b.waardeklasse_new = a.waardeklasse;
Use the above query - in this you can use the left join and where condition to speed up the query.
Also don't use the index for the second table which has 46 record this will affect the performance - if the table has less records then index will create more burden in this case full table scan without index is lot better. Also if you have a cluster index in the first table(7 million) remove them and run the query, because for each and every update you perform default table structure And page alignment will be updated in the clustered index. Hope this helps..!

Answer 2

First, you don't need the where clause. Second, remove the index hints:
update src_woz_waardeklasse_2011 ww inner join
waardeklasse_average wa
on wa.waardeklasse_new = ww.waardeklasse
set ww.woz_value = wb.average ;
Then, try an index on src_woz_waardeklasse_2011(waardeklasse). This should improve the execution plan.
You might also check that the 46 records in the second table actually correspond to 46 updates. If the join conditions are wrong, you could be updating all the records.
EDIT:
Indexes have nothing to do with your problem. Updating 7 million records takes a long time. You might consider creating the data you want in a temporary table and then truncating the original table and inserting the new rows into it. Otherwise, batch the updates a few rows at a time.

Answer 3

update src_woz_waardeklasse_2011 a use index(waardeklasse_main,woz_val)
inner join waardeklasse_average b use index (waardeklasse)
on b.waardeklasse_new = a.waardeklasse
set a.woz_value = b.average
Where condition is not needed. As you had already mention that condition in On clause.
Try above query.