MySQL - insert if doesn't exist yet

问题:

I want to execute this MySQL query:

INSERT INTO `cron-stats` (`user`) VALUES (".(int)$d['by-user'].")

Whenever such user doesn't exist yet, as in:

SELECT 1
FROM `cron-stats`
WHERE `user` = ".(int)$d['by-user']."

How can I execute this in one query?

回答1:

you can use ON DUPLICATE KEY UPDATE

INSERT INTO `cron-stats` (`user`) VALUES ('yourValue')
ON DUPLICATE KEY UPDATE user = user;

• ON DUPLICATE KEY UPDATE

but in order to perform the INSERT statement well, you need to set a UNIQUE index on column user.

if the column has no index yet, execute the statement below,

 ALTER TABLE `cron-stats` ADD CONSTRAINT tb_un UNIQUE (`user`)

回答2:

A little bit hacky, but if you use a SELECT derived table instead of VALUES you can do:

INSERT INTO `cron-stats`(`user`)
SELECT u
FROM (SELECT @dByUser AS u) x
WHERE NOT EXISTS(SELECT 1 FROM `cron-stats` WHERE `user` = @dByUser)

SQL Fiddle demo

回答3:

You can try this using if else condition

$chk = mysql_query("select 'the username' FROM `cron-stats`");
$rs = mysql_fetch_array($chk);
if($rs == "")
{
    $ins = mysql_query("INSERT INTO `cron-stats` (`user`) VALUES ('.(int)$d['by-user'].')");
} 
else{
    echo "Duplicate entry";
}