Issue with update + insert in PDO mysql driver

[dimasikturbo]

When same data is stored under same key PDO mysql driver return 0 number of updated rows and as a result insert triggers error "SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry"

MySQL has a special SQL extension INSERT ON DUPLICATE KEY UPDATE which can be used instead of UPDATE + INSERT.

[coveralls]

Changes Unknown when pulling cbf3a87 on dimasikturbo:master into ** on frqnck:master**.

[frqnck]

@dimasikturbo Many thanks for your PR.

Why not add the ON DUPLICATE KEY UPDATE statement directly to $sql_definitions['insert'] ?

e.g.

'insert'    => 'INSERT INTO `%s` (`key`, `data`, `tags`, `expire`, `dated`) VALUES (:key, :data, :tags, :exp, :dated) ON DUPLICATE KEY UPDATE `data`=VALUES(`data`), `tags`=VALUES(`tags`), `expire`=VALUES(`expire`);',

[dimasikturbo]

To avoid unnecessary update query for every new entry. But at the same time, usually read/write ratio in cashes is really high, so it might be not a big deal.

[frqnck]

hum... I don't think it makes any difference other than adding some extraenous code.

Thank you for the contrib -- I will merge.