mysql update table field from another table - php

Question

i have these set of tables
CREATE TABLE `staff` (
`id` mediumint(8) NOT NULL AUTO_INCREMENT,
`uid` varchar(128) NOT NULL,
`name` varchar(128) NOT NULL,
`deptname` varchar(128) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;
INSERT INTO `staff` (`id`, `uid`, `name`, `deptname`) VALUES
(1,'A100','John','Finance'),
(2,'A101','Joana','ICT'),
(3,'A103','Darrel','Maintenance'),
(4,'A104','Smith','HR');
CREATE TABLE `department` (
`id` mediumint(8) NOT NULL AUTO_INCREMENT,
`deptid` int(11) UNSIGNED NOT NULL DEFAULT '0',
`deptname` varchar(128) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;
INSERT INTO `department` (`id`, `deptid`, `deptname`) VALUES
(1,'100','ICT'),
(2,'200','Finance'),
(8,'300','HR'),
(11,'400','Maintenance'),
(12,'500','Backup');
CREATE TABLE `new_staff` (
`id` mediumint(8) NOT NULL AUTO_INCREMENT,
`uid` varchar(128) NOT NULL,
`name` varchar(128) NOT NULL,
`deptid` int(11) UNSIGNED NOT NULL DEFAULT '0',
PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;
INSERT INTO `new_staff` (`id`, `uid`, `name`, `deptid`) VALUES
(1,'A100','John','600'),
(2,'A103','Darrel','400'),
(3,'A104','Smith','300'),
(4,'A101','Joana','500'),
(5,'A105','Fran','800');
i would like to update the deptid field in the new_staff table to have the correct deptid as listed in the department table
in the new_staff table deptid are currently wrong for John and Joana
this is what i tried so far
// list all deptid exists
$result=$mysqli->query("SELECT deptid FROM department");
while ($rows=mysqli_fetch_array($result))
{$deptid[]=$rows['deptid'];}
$deptidarray = implode(', ', $deptid);
echo "<br>";
//echo "$deptidarray<br>";
$query=$mysqli->query("SELECT deptid from new_staff WHERE deptid not in ($deptidarray)");
echo "<br>";
$rowtotal = mysqli_num_rows($query);
if($rowtotal>0){
while ($row=mysqli_fetch_array($query))
{
$deptid=$row['deptid'];
// echo "$deptid,";
//$query=$mysqli->query("UPDATE new_staff set deptid='$deptid' WHERE ");
}
}
else
{
// not found
}
is this possible to do entirely in mysql?

Answer 1

UPDATE new_staff AS ns
JOIN staff AS s ON
ns.uid = s.uid // 1. Get same users from 2 tables
JOIN department AS d ON
s.deptname = d.deptname // 2. Get department
SET ns.deptid = d.deptid // 4. Update correct department id
WHERE ns.deptid != d.deptid; // 3. Get users where department is incorrect
Run SELECT query first before updating to verify the updates.
SELECT ns.*, d.deptid AS new_dept_id
FROM new_staff AS ns
JOIN staff AS s ON
ns.uid = s.uid
JOIN department AS d ON
s.deptname = d.deptname
WHERE ns.deptid != d.deptid;