sql update statement with from clause for validation? - mysql

Question

I have an update operation that I perform on multiple users at once (the value stays the same). Is it possible to join tables to an update statement for reasons of validation?
For instance, here is my statement at the moment :
$user_set = array(1, 5, 10, 15, .....)
//update 'changed' status for ALL selected users at once
$stmt = $db->prepare("
UPDATE users
SET changed = ?
WHERE user_id IN(". implode(', ', array_fill(1,count($user_set),'?')) .")
");
array_unshift($user_set, 1);
$stmt->execute($user_set);
In a perfect scenario I would like to join one table (computers) to the users table to validate account ownership and if this update is 'valid' and should occur or not.
I found out earlier I can do EXACTLY that with DELETE, but can it be done with UPDATE as well? Example delete using validation I want :
$selected = array(1, 5, 10, 15, .....)
$stmt = $db->prepare("
DELETE del_table.*
FROM some_table as del_table
LEFT JOIN
users
on users.user_id = del_table.user_id
LEFT JOIN
computers
on computers.computer_id = users.computer_id
WHERE computers.account_id = ? AND del_table.activity_id IN(". implode(', ', array_fill(1,count($selected),'?')) .")
");
// use selected array and prepend other data into the array so binding and execute work in order
array_unshift($selected, $_SESSION['user']['account_id']);
$stmt->execute($selected);
EDIT (SOLUTION) :
Thanks Alex... it works!
$selected = array(5,10,12,13);
$stmt = $db->prepare("
UPDATE users
INNER JOIN computers
on computers.computer_id = users.computer_id
SET changed = ?
WHERE computers.account_id = ? AND users.user_id IN(". implode(', ', array_fill(1,count($selected),'?')) .")
");
array_unshift($selected, 1, $_SESSION['user']['account_id']);
$stmt->execute($selected);

Answer 1

Yes, you can, as documented here under the multi-table syntax section.
UPDATE [LOW_PRIORITY] [IGNORE] table_references
SET col_name1={expr1|DEFAULT} [, col_name2={expr2|DEFAULT}] ...
[WHERE where_condition]
You just need to make sure you order the statements correctly.
UPDATE my_table
INNER JOIN other_table
ON my_table.col2 = othertable.col2
SET my_table.col = 'foo'
WHERE other_table.col = 'bar'

Answer 2

try this
$stmt = $db->prepare("
UPDATE users
SET changed = ?
from users
JOIN computers on computers.computer_id = users.computer_id
WHERE user_id IN(". implode(', ', array_fill(1,count($user_set),'?')) .")
");