mysql更新语句

Question

下面的表：p_id是父id，old_id是以前的父id，现在需要把p_id的值改成id
比如第一条数据，之前的父id是10，其实对应的是第二跳记录，所以更新后，p_id=2

更新后的结果：

这样的更新语句sql如何写？
需要做的事情：通过p_id找到old_id,这时候的id就是要更新的值；
第一条记录p_id==10，p_id=old_id=10的是第二天记录，把p_id更新成2

Answer 1

I haven’t written a Mysql query operation for a long time, but I have an idea. For the records in the above table, p_id and old_id are in one table, and both comparison operations and update operations are required. Suggestion:

Step 1: Split a temporary table based on the main table tmp_id, old_tmp_id (corresponding to old_id in the main table)

• tmp_id old_tmp_id

• 1 30

• 2 10

• 3 20

Step 2: left join query, where p_id == old_tmp_id, set p_id = tmp_id

Answer 2

表名test

update test t1
inner join test t2 on t1.p_id = t2.old_id
set t1.p_id = t2.id

Answer 3

If you can’t get one SQL statement, just put it in the transaction and update it twice

Answer 4

UPDATE test t1
INNER JOIN test t2 ON t1.p_id = t2.old_id
SET t1.p_id = t2.id