Part of the system I'm working on at the moment involves a log in mysql, with counts being frequently updated.
The data being inserted is of the format:
date | name | count |
-----------+------+-------+
2009-01-12 | alan | 5 |
2009-01-12 | dave | 2 |
2009-01-12 | mary | 1 |
This data is parsed regularly from a flat file, summarised as above in preparation for a db insert/update - the unique key on the database is the (date, name)
pair.
Previously, this system would check the existing table for any records for a given date
and name
pair before deciding on an update or insert.
The problem we're having is, as this table grows, the response time isn't getting any better, and we want to reduce the number of queries as much as possible.
The system was recently updated to run a INSERT ... ON DUPLICATE KEY UPDATE
query, which has reduced the number of select
s marginally, but our common case by some distance is the update
.
I'm wondering if anyone knows of a mysql function that's essentially INSERT ... ON DUPLICATE KEY UPDATE
in reverse, i.e. will try to update a row, if none match then perform the insert?
I didn't make it too clear above, what I would like to do when I have the record ('2009-01-12','alan','5')
for example, is:
UPDATE table SET count = count+5 WHERE date = '2009-01-12' and name = 'alan';
and if the above fails, insert the above data. The need to increment a counter is why REPLACE
won't work. Replace performs a delete & insert, and doesn't let you refer to the row being deleted, so count = count + 5
wouldn't increment the previous count
value for by 5.
@jasoncohen - the INSERT ... ON DUPLICATE KEY UPDATE
does do the job, but I'm asking if there's a more optimal way to do this.
Sorry for any confusion resulting from the poor original phrasing!
When you insert a new row into a table if the row causes a duplicate in UNIQUE index or PRIMARY KEY , MySQL will issue an error. However, if you specify the ON DUPLICATE KEY UPDATE option in the INSERT statement, MySQL will update the existing row with the new values instead.
Often you have the situation that you need to check if an table entry exists, before you can make an update. If it does not exist, you have to do an insert first. Unfortunately, this the 'ON DUPLICATE KEY' statement only works on PRIMARY KEY and UNIQUE columns.
There are three ways you can perform an “insert if not exists” query in MySQL: Using the INSERT IGNORE statement. Using the ON DUPLICATE KEY UPDATE clause. Or using the REPLACE statement.
Using INSERT IGNORE This means that an INSERT IGNORE statement which contains a duplicate value in a UNIQUE index or PRIMARY KEY field does not produce an error, but will instead simply ignore that particular INSERT command entirely.
It's just the same. With "UPDATE ... ON NO KEY INSERT", the database engine will still have to check first if there is something to update. Hence no need for a separate construct even if update is most common
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With