PHP查询时间（）表单mysql

I want that my PHP checks if the time in the mysql db is the same, and if not that it will be changed.

This is what I got:

<?php
$last_time_check=mysqli_query($con,"SELECT `time` FROM `servervars`");
if((time()-$last_time_check) >=1)
{
   mysqli_query($con, 'UPDATE `servervars` SET `time`='.$time.' WHERE ID=1');
}
?>

$con is the connection to the DB.
Current value 'time' in servervars: 1412448339
Value 'ID' is 1

I do something wrong, but I just cannot find where it's going wrong.

The Fix

I've removed the variable $last_time_check and only checked if the time could get changed. If this happends then it will send another message to the client.

mysqli_query($con, 'UPDATE `servervars` SET `time` = UNIX_TIMESTAMP() WHERE ID = 1 AND UNIX_TIMESTAMP() - `time` >= 1');
    if ($con->affected_rows)
    {
        // at least 1 second has elapsed, do stuff
    }

MySQL has an equivalent to time(), its the function UNIX_TIMESTAMP(). Differently though, it can take a DATETIME as parameter to convert it into UNIX time, but when used without parameters its the same as UNIX_TIMESTAMP(NOW()).

UPDATE servervars SET time = UNIX_TIMESTAMP() WHERE ID = 1

Update

Ok so about the other issues. You are doing it all wrong. mysqli_query does not return the value directly. To fetch the value of time from the database, you need 3 steps:

$result = $con->query('SELECT `time` FROM `servervars` WHERE ID = 1'); // fetch result set
$row    = $result->fetch_row(); // fetch a row from the result set, as an array
$last   = $row[0]; // get the first element from the row you just fetched

Notice $con->query() can fail if theres a problem with the connection, the database, the table, or the query syntax itself, and $result->fetch_row() can fail if there are no results for the query. You should validate them before proceeding to the next step.

Alternatively, you can do this:

$con->query('UPDATE `servervars` SET `time` = UNIX_TIMESTAMP() WHERE ID = 1 AND UNIX_TIMESTAMP() - `time` >= 1');
if ($con->affected_rows)
{
    // at least 1 second has elapsed, do stuff
}

This way we shortened your solution to a single query, that updates the field if necessary and report back that it happened or not..