在我的MySQL表上运行一个更新，它将用另一个字段的内容替换1字段的内容

Question

I am trying to run an update on a MySQL table that will swap the contents of 1 field with the contents of another (both in the same table).

Here is the basic structure of the table:

id      SKU     related
==      ===     =======
1234    SKU001  1234,8889,2209
5544    SKU855  2209,1234
2209    SKUYYT  5544

What I need to do is swap the related field for the relavent SKU (so that it lists the sku's instead of the id's). So it would end up looking like this:

id      SKU     related
==      ===     =======
1234    SKU001  SKU001,SKU111,SKUYYT
5544    SKU855  SKUYYT,SKU001
2209    SKUYYT  SKU855

So what I'm trying to achieve is the id in the related field would have been replaced with the SKU that relates to that id.

What I'm currently doing is this:

SELECT id, sku FROM my_table

Then looping through all id's with PHP and updating the table like so:

UPDATE my_table SET related = REPLACE(related, '5544', 'SKU855');

This seems to work but I have 9000+ rows and multiple id's in the related column and it's taking hours to complete

Can anyone suggest a better way of achieving this? (Ideally in MySQL)

Many thanks

Answer 1

If you have access to PHP with this update, I would suggest you do the following:

$rows = some_method_to_load_all_rows_from_your_table();
$id_to_sku = array();

// Loop through all rows to cache their SKU numbers and directly associate them to their row's PK.
foreach ($rows as $row) {
    $id_to_sku[$row['id']] = $row['SKU'];
}

// Loop through all rows a second time to then break apart, find, and replace the related IDs.
foreach ($rows as $index => $row) {
    $related_ids = explode(',', $row['related']);
    foreach($related_ids as &$related_id) {
        if (isset($id_to_sku[$related_id]]) {
            $related_id = $id_to_sku[$related_id]];
        } // else the ID couldn't be found.
    }
    $rows[$index]['related'] = implode(',', $related_ids);
}

// $rows now contains the related string with the SKU numbers instead of ID numbers.
method_to_update_all_rows_with_new_related_value($rows);

Essentially, doing this in raw SQL is going to be very difficult, and you will be left with a very complex query. The best way is to abstract the detecting and replacing of the IDs / SKU numbers into PHP, where this becomes a much easier and more readable platform to work on.

The code loads all rows in the table, then loops through each row to cache it's ID and SKU number separately.

Then, we loop through each row again, break apart the related field into an array of IDs, replace those IDs with their correct SKU code using the cache we created, and insert them back into $rows .

$rows becomes the new updated table set. From there, it's a case of creating a giant UPDATE statement, or looping through each row and executing a single UPDATE statement for each one. Looping in PHP and issuing an UPDATE for each row would be slower as making a query has overhead. But you can also implement the loop in SQL, using stored procedure, avoiding the overhead on communication between your application and database.

Answer 2

/*
create my_table_temp with same structure as in my_table
*/
$mapping = array();
$sth = $dbh->prepare("SELECT id, SKU FROM my_table");
$sth->execute();
$rows = $sth->fetchAll(PDO::FETCH_ASSOC);
foreach($rows as $row) {
    $mapping[$row['id']] = $row['SKU'];
}

$sql = 'insert into my_table_temp(id, SKU, related) VALUES ';
$params = array();

$sth = $dbh->prepare("SELECT * FROM my_table");
$sth->execute();
$rows = $sth->fetchAll(PDO::FETCH_ASSOC);
foreach($rows as $row) {
    $related = explode(',', $row['related']);
    foreach($related as &$val) {
        $val = $mapping[$val];
    }
    $sql .= '(?, ?, ?),';
    $params[] = $row['id'];
    $params[] = $row['SKU'];
    $params[] = implode(',', $related); 
}

$sql = rtrim($sql, ',');
$sth = $dbh->prepare($sql);
$sth->execute($params);

/*
update my_table 
set related = q.related
from (
    select sku, related 
    from my_table_temp
) q
where my_table.sku = q.sku;
drop table my_table_temp;
*/

Answer 3

When You are asking to do it in mysql , then it would be possible by using CURSOR and dynamic query.

DELIMITER //
CREATE PROCEDURE `all_update`()
BEGIN
DECLARE ids INT;
DECLARE sname VARCHAR(255);

DECLARE finished INTEGER DEFAULT 0;

DECLARE cursor1 CURSOR FOR SELECT id,SKU FROM testing;  
DECLARE CONTINUE HANDLER FOR NOT FOUND SET finished = 1;

OPEN cursor1;
update_table: LOOP
    FETCH cursor1 INTO ids,sname;
    IF finished = 1 THEN
    LEAVE update_table;
    END IF;
    SET @s =  CONCAT('UPDATE testing SET related = REPLACE(related,', ids,', "',sname,'")');

            PREPARE stmt1 FROM @s;
            EXECUTE stmt1;
            DEALLOCATE PREPARE stmt1;


END LOOP update_table;

CLOSE cursor1;

END//

Fiddle is http://sqlfiddle.com/#!2/298a7/1