<p style="white-space:normal;">我目前有三个表格：</p><p style="white-space:normal;">users表格 // 数据在注册时插入<pre class="brush:php;toolbar:false;">usersId //PRIMARY KEY userfName userlName userUid email userPwd dateTime</pre> <p><code>parent</code> table</p> <pre class="brush:php;toolbar:false;">id //PRIMARY KEY mFname mLname mEmail mPhone fFname fLname fEmail fPhone addressL1 addressL2 city stateAbbr zip created_at user_id //FOREIGN KEY</pre> <p>我使用了users表格中的email列以及mEmail或fEmail来将usersId插入到parents表格中。</p> <p><code>Children</code> Table</p> <pre class="brush:php;toolbar:false;">child_id //PRIMARY KEY child1Name dobChild1 ageChild1 child2Name dobChild2 ageChild2 child3Name dobChild3 ageChild3 child4Name dobChild4 ageChild4 child5Name dobChild5 ageChild5 child6Name dobChild6 ageChild6 child7Name dobChild7 ageChild7 child8Name dobChild8 ageChild8 child9Name dobChild9 ageChild9 child10Name dobChild10 ageChild10 parent_id //FOREIGN KEY</pre> <p>在儿童桌和其他两个表之间没有共同的数值。我的期望是在用户表和父表之间进行验证，如果用户表的usersId和父表的user_id相等，则将该值插入到children表的parent_id中。这种操作是否可行？我考虑使用交叉连接（cross join），但我担心随着数据库中的条目数量增长，性能会受到影响。</p> <pre class="brush:php;toolbar:false;">SELECT usersId FROM users; SELECT user_id FROM parent; UPDATE children (parent_Id) INNER JOIN parent ON children.parent_id = users.usersId UPDATE children SELECT usersId FROM users cross JOIN children.parent_id ON users.usersId = children.parent_id UPDATE children INNER JOIN users (INNER JOIN parent ON users.userId = parent.userId) ON users.usersId = parent.user_id SET children.parent_id = parent.user_Id;</pre> <p>我已经尝试了每一种方法，但都没有成功。我还尝试改变连接的顺序，但也没有用。非常感谢您提供的任何帮助。</p>

UPDATE Children c
SET c.parent_id = (
  SELECT p.user_id
  FROM users u
  JOIN parent p ON u.email = p.mEmail OR u.email = p.fEmail
  WHERE c.parent_id IS NULL -- Only update rows with NULL parent_id to avoid overwriting existing values
  LIMIT 1 -- Assuming you want to update one parent_id per child record; you may modify this as needed
);