mysql相同编码的两条数据，两值相加更新到第三个值

Question

怎样将编码code相同的两条数据，字段new_warehouse_num 与 old_warehouse_num的值相加得到总和sum

Answer 1

UPDATE table_name t1
JOIN (
    SELECT code, SUM(new_warehouse_num + old_warehouse_num) AS total_sum
    FROM table_name
    GROUP BY code
) t2 ON t1.code = t2.code
SET t1.sum = t2.total_sum;