CREATE TEMPORARY TABLE temp_table AS (
  SELECT wp_postmeta.post_id, 
  	wp_postmeta.meta_value AS sale_price, 
  	pm1.meta_value AS regular_price,
  	pm2.meta_value AS price
  FROM wp_postmeta
  LEFT JOIN wp_postmeta pm1 ON pm1.post_id = wp_postmeta.post_id AND pm1.meta_key = '_regular_price'
  LEFT JOIN wp_postmeta pm2 ON pm2.post_id = wp_postmeta.post_id AND pm2.meta_key = '_price'
  WHERE wp_postmeta.meta_key = '_sale_price' AND wp_postmeta.meta_value IS NOT NULL AND wp_postmeta.meta_value <> '' 
);

UPDATE wp_postmeta pm1
INNER JOIN temp_table pm2 ON pm1.post_id = pm2.post_id
SET pm1.meta_value = pm2.sale_price
WHERE pm1.meta_key = '_price' 
AND pm2.price <> pm2.sale_price
-- AND pm1.post_id IN (5610)
;

DROP TEMPORARY TABLE temp_table;

-- select * from temp_table where price <> sale_price;