using mysql key/index for query performance improvement - mysql

Question

I want all the promotions which were active between specific date. Once the promotion is activated createdOnDt is changed to now() and updatedOnDt remains null. When promotion is deactivated updatedOnDt is changed to now(). Here is table structure
CREATE TABLE promotions
(id bigint NOT NULL AUTO_INCREMENT,
promotionId bigint NOT NULL,
promotionName varchar(255) CHARACTER SET utf8mb4
COLLATE utf8mb4_unicode_ci DEFAULT NULL,
clientId int NOT NULL,
subClientId int DEFAULT NULL,
createdOnDt datetime DEFAULT NULL,
updatedOnDt datetime DEFAULT NULL,
PRIMARY KEY (id),
KEY clientId_subClientId (clientId,subClientId)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=latin1
Now, active promotions between date can be found out using,
select p.*
from promotions p
where p.createdOnDt >= (:fromDate)
and p.createdOnDt <= (:toDate)
and p.clientId = (:clientId) ```
for this query performance is as follows,
+----+-------------+-------+------------+------+-------------------------------+-------------------------------+---------+-------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+-------+------------+------+-------------------------------+-------------------------------+---------+-------+------+----------+-------------+
| 1 | SIMPLE | p | NULL | ref | clientId_subClientId | clientId_subClientId | 4 | const | 2 | 50.00 | Using where |
+----+-------------+-------+------------+------+-------------------------------+-------------------------------+---------+-------+------+----------+-------------+
but when I want to fetch currently running promtions as well using following query,
select p.*
from promotions p
where p.createdOnDt >= (:fromDate)
and p.createdOnDt <= (:toDate)
or (p.createdOnDt <= (:fromDate)
and p.updatedOnDt is null
)
and p.clientId = (1957)
for this query following is the performance,
+----+-------------+-------+------------+------+-------------------------------+------+---------+------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+-------+------------+------+-------------------------------+------+---------+------+------+----------+-------------+
| 1 | SIMPLE | p | NULL | ALL | clientId_subClientId | NULL | NULL | NULL | 2 | 50.00 | Using where |
+----+-------------+-------+------------+------+-------------------------------+------+---------+------+------+----------+-------------+
this is full table scan.
I want to know,
can we get the required data without updatedOnDt column ?
and if updatedOnDt is necessary how to improve performance of query ? also
if createdOnDt is let's say 2nd Aug and updatedOnDt is 6th Aug for promotion X, then if searched between 3rd Aug and 5th Aug query should return promotion X because it was active during selected date range. I tried adding key for createdOnDt as well as on updatedOnDt. but still there was no performance improvement.

Answer 1

The first query needs INDEX(clientId, createdOnDt).
The second query does not test both sides of the OR against clientId. This smells like a flaw.
In the second query, OR is the performance killer...
select p.*
from promotions p
where p.createdOnDt >= (:fromDate)
and p.createdOnDt <= (:toDate)
and p.clientId = (1957)
UNION ALL
select p.*
from promotions p
where p.createdOnDt <= (:fromDate)
and p.updatedOnDt is null
and p.clientId = (1957)
The previous index, plus this, are needed:
INDEX(clientId, updatedOnDt, createdOnDt)
Be aware that :toDate should end with 23:59:59, else the query will not include the last "day".
Also note that p.createdOnDt = (:fromDate) shows up in both sides of the UNION ALL. This may not be what you wanted.