MySQL update join with limit

Question

I would like to know how to update a table, with values from another table, by the trick is I need to set a limit because I have thousands of rows to update, and PHPmyadmin can\

Answer 1

It's rather unconventional , but it should help you in a pinch

SET @tmp_c = 0;
UPDATE
    table1
INNER JOIN table2 ON table1.id = table2.id
INNER JOIN table3 ON table2.id = table3.id
SET
    table1.remove_date = NOW() - INTERVAL 5 MONTH
WHERE
    table1.active = 1
AND
    (IF (table1.active = 1, @tmp_c := @tmp_c + 1 , 0 )) //This is to only increment the counter if the whole where matches
AND
    @tmp_c <= 15 //Start ignoring row items as soon as it exceeds the limit amount

Answer 2

sqlFiddle in this example I am only doing 5 rows, you can change the limit to 0,100 if you'd like

UPDATE wp_postmeta,
      (SELECT oldmap,newmap
       FROM wp_map 
       ORDER BY oldmap,newmap limit 0,5)as wp_map
SET wp_postmeta.meta_value = wp_map.newmap
WHERE wp_map.oldmap = wp_postmeta.meta_value

Answer 3

You can try it this way

UPDATE wp_postmeta t JOIN
(
    SELECT p.meta_id, m.newmap
      FROM wp_postmeta p JOIN wp_map m
        ON p.meta_value = m.oldmap
     ORDER BY p.meta_id
     LIMIT 100
) s
   ON t.meta_id = s.meta_id
  SET t.meta_value = s.newmap;

Here is SQLFiddle demo