Multiple Updates in MySQL

Question

I know that you can insert multiple rows at once, is there a way to update multiple rows at once (as in, in one query) in MySQL?

Edit: For example I have the following

Name   id  Col1  Col2
Row1   1    6     1
Row2   2    2     3
Row3   3    9     5
Row4   4    16    8

I want to combine all the following Updates into one query

UPDATE table SET Col1 = 1 WHERE id = 1;
UPDATE table SET Col1 = 2 WHERE id = 2;
UPDATE table SET Col2 = 3 WHERE id = 3;
UPDATE table SET Col1 = 10 WHERE id = 4;
UPDATE table SET Col2 = 12 WHERE id = 4;

Answer 1

Why does no one mention multiple statements in one query?

In php, you use multi_query method of mysqli instance.

From the php manual

MySQL optionally allows having multiple statements in one statement string. Sending multiple statements at once reduces client-server round trips but requires special handling.

Here is the result comparing to other 3 methods in update 30,000 raw. Code can be found here which is based on answer from @Dakusan

Transaction: 5.5194580554962
Insert: 0.20669293403625
Case: 16.474853992462
Multi: 0.0412278175354

As you can see, multiple statements query is more efficient than the highest answer.

If you get error message like this:

PHP Warning:  Error while sending SET_OPTION packet

You may need to increase the max_allowed_packet in mysql config file which in my machine is /etc/mysql/my.cnf and then restart mysqld.

Answer 2

With PHP I did this. Use semicolon, split it into array and then submit via loop.

$con = new mysqli('localhost','user1','password','my_database');
$batchUpdate = true; /*You can choose between batch and single query */
$queryIn_arr = explode(";", $queryIn);

if($batchUpdate)    /* My SQL prevents multiple insert*/
{
    foreach($queryIn_arr as $qr)
    {
        if(strlen($qr)>3)
        {
            //echo '<br>Sending data to SQL1:<br>'.$qr.'</br>';
            $result = $conn->query($qr);
        }

    }
}
else
{
    $result = $conn->query($queryIn);
}
$con->close();

Answer 3

UPDATE `your_table` SET 

`something` = IF(`id`="1","new_value1",`something`), `smth2` = IF(`id`="1", "nv1",`smth2`),
`something` = IF(`id`="2","new_value2",`something`), `smth2` = IF(`id`="2", "nv2",`smth2`),
`something` = IF(`id`="4","new_value3",`something`), `smth2` = IF(`id`="4", "nv3",`smth2`),
`something` = IF(`id`="6","new_value4",`something`), `smth2` = IF(`id`="6", "nv4",`smth2`),
`something` = IF(`id`="3","new_value5",`something`), `smth2` = IF(`id`="3", "nv5",`smth2`),
`something` = IF(`id`="5","new_value6",`something`), `smth2` = IF(`id`="5", "nv6",`smth2`) 

// You just building it in php like

$q = 'UPDATE `your_table` SET ';

foreach($data as $dat){

  $q .= '

       `something` = IF(`id`="'.$dat->id.'","'.$dat->value.'",`something`), 
       `smth2` = IF(`id`="'.$dat->id.'", "'.$dat->value2.'",`smth2`),';

}

$q = substr($q,0,-1);

So you can update hole table with one query

Answer 4

Yes, that's possible - you can use INSERT ... ON DUPLICATE KEY UPDATE.

Using your example:

INSERT INTO table (id,Col1,Col2) VALUES (1,1,1),(2,2,3),(3,9,3),(4,10,12)
ON DUPLICATE KEY UPDATE Col1=VALUES(Col1),Col2=VALUES(Col2);

Answer 5

Not sure why another useful option is not yet mentioned:

UPDATE my_table m
JOIN (
    SELECT 1 as id, 10 as _col1, 20 as _col2
    UNION ALL
    SELECT 2, 5, 10
    UNION ALL
    SELECT 3, 15, 30
) vals ON m.id = vals.id
SET col1 = _col1, col2 = _col2;