Question

I’m trying to optimize a view in MySql. The view takes 0-5 records from a table and turns them into 1 record. The view works, but is slowing down as the # of records in the property_log table increases.

For example, data that looks like this:

mysql> select * from property_log where event_id = 1144882;
+----------+--------------+------------------------------+
| event_id | log_key      | log_value                    |
+----------+--------------+------------------------------+
|  1144882 | userId       | 1000                         |
|  1144882 | licenseId    | 3                            |
|  1144882 | messageTypeId| 7                            |
|  1144882 | message      | Sample message               |
|  1144882 | op           | tracking                     |
+----------+--------------+------------------------------+

Gets turned into 1 record:

mysql> select * from view_logged_property where id = 1144882
+---------+--------+-----------+---------------+-------------------+
| ID      | UserID | LicenseID | MessageTypeID | Message           |
+---------+--------+-----------+---------------+-------------------+
| 1144882 | 1000   | 3         | 7             | Sample message    |
+---------+--------+-----------+---------------+-------------------+

Edit: Important Note – Not all 5 records will be present all the time. For example, the data could also look like this:

mysql> select * from property_log where event_id = 1144882;
+----------+--------------+------------------------------+
| event_id | log_key      | log_value                    |
+----------+--------------+------------------------------+
|  1144882 | userId       | 1000                         |
|  1144882 | messageTypeId| 7                            |
|  1144882 | message      | Sample message               |
|  1144882 | op           | tracking                     |
+----------+--------------+------------------------------+

The view I’m currently using to do this is the following:

DROP VIEW IF EXISTS view_logged_property;
CREATE VIEW view_logged_property as (
  SELECT
    p.event_id as ID,
    (select log_value from property_log where log_key = "userId" and event_id = p.event_id) as UserID,
    (select log_value from property_log where log_key = "licenseId" and event_id = p.event_id) as LicenseID,
    (select log_value from property_log where log_key = "messageTypeId" and event_id = p.event_id) as MessageTypeID,
    (select log_value from property_log where log_key = "message" and event_id = p.event_id) as Message
  FROM
    logging_event p
  WHERE
    p.event_id in (select event_id from property_log where log_key = "op" and log_value = "tracking")
);

What’s the best way to write this view so it’ll perform well even as the # of records in the “property_log” table increases?

Answer 1

I would use joins in this case.

Changed after comment left joins should solve problem.

DROP VIEW IF EXISTS view_logged_property;
CREATE VIEW view_logged_property as (
    select 
        p1.event_id as ID, 
        p5.log_value as UserID, 
        p2.log_value as LicenseID, 
        p3.log_value as MessageTypeID, 
        p4.log_value as Message
    from property_log p1  
    left join property_log p5 on p1.event_id = p5.event_id and p5.log_key = 'userId'
    left join property_log p2 on p1.event_id = p2.event_id and p2.log_key = 'licenseId'
    left join property_log p3 on p1.event_id = p3.event_id and p3.log_key = 'messageTypeId'
    left join property_log p4 on p1.event_id = p4.event_id and p4.log_key = 'message'
    where p1.log_key = 'op' and p1.log_value = 'tracking'
);

Could you test it on your data?

Index on pair event_id, log_key might be required, sth like below:

 create index event_key_idx on property_log(event_id, log_key);

SQL Fiddle example