How to use SQL - INSERT...ON DUPLICATE KEY UPDATE?

Question

Hi, I have a script which captures tweets and puts them into a database. I will be running the script on a cronjob and then displaying the tweets on my site from the database to prevent hitting the limit on the twitter API.

So I don't want to have duplicate tweets in my database, I understand I can use 'INSERT...ON DUPLICATE KEY UPDATE' to achieve this, but I don't quite understand how to use it.

My database structure is as follows.

Table - Hash id (auto_increment) tweet user user_url

And currently my SQL to insert is as follows:

$tweet = $clean_content[0];
$user_url = $clean_uri[0];
$user = $clean_name[0];

$query='INSERT INTO hash (tweet, user, user_url) VALUES ("'.$tweet.'", "'.$user.'", "'.$user_url.'")';
mysql_query($query);

How would I correctly use 'INSERT...ON DUPLICATE KEY UPDATE' to insert only if it doesn't exist, and update if it does?

Thanks

Answer 1

Try using:

$query='INSERT INTO hash (tweet, user, user_url) 
        VALUES ("'.$tweet.'", "'.$user.'", "'.$user_url.'") 
        ON DUPLICATE KEY UPDATE tweet = VALUES(tweet)';

Answer 2

ON DUPLICATE KEY UPDATE doesn't seem to be the right solution here, as you don't want to update if the value is already in the table.

I would use Twitter's own unique Status ID field (which should be unique for each tweet) instead of your hash id. Add that as a field on your table, and define it as the primary key (or as a unique index.) Then use REPLACE INTO, including the status ID from Twitter.

This has the advantage that you can always track your record back to a unique Tweet on twitter, so you could easily get more information about the Tweet later if you need to.

Answer 3

you need some UNIQUE KEY on your table, if user_url is tweer_url, then this should fit (every tweet has a unique url, id would be better).

CREATE TABLE `hash` (
  `user_url` ...,
  ...,
  UNIQUE KEY `user_url` (`user_url`)
);

and its better to use INSERT IGNORE on your case

$query='INSERT IGNORE INTO hash (tweet, user, user_url) VALUES ("'.$tweet.'", "'.$user.'", "'.$user_url.'")';

ON DUPLICATE KEY is useful when you need update existing row but you want to insert just once