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UPDATE table_1 AS t1, table_2 AS t2
  SET
    t1.name = t2.title,
    t1.descr = t2.description,
    t1.price = t2.price,
    t1.available = t2.stock
  WHERE t1.productId = t2.sku

Taken from forum while browsing to find for solution. This query will took some time when dealing with thousands record in both table.