关于主键和插入的简单mysql问题

2022-01-09 00:00:00 insert mysql primary-key

在mysql中，当自动递增时，如何获取用于插入操作的主键.

In mysql, how do I get the primary key used for an insert operation, when it is autoincrementing.

基本上，我希望在语句完成时返回新的自动增量值.

Basically, i want the new autoincremented value to be returned when the statement completes.

谢谢！

推荐答案

您的澄清评论说您有兴趣确保 LAST_INSERT_ID() 在发生另一个并发 INSERT 时不会给出错误结果.请放心，无论其他并发活动如何，使用 LAST_INSERT_ID() 都是安全的.LAST_INSERT_ID() 仅返回当前会话期间生成的最新 ID.

Your clarification comment says that you're interested in making sure that LAST_INSERT_ID() doesn't give the wrong result if another concurrent INSERT happens. Rest assured that it is safe to use LAST_INSERT_ID() regardless of other concurrent activity. LAST_INSERT_ID() returns only the most recent ID generated during the current session.

你可以自己试试:

  1. 打开两个shell窗口，运行mysql每个客户端并连接到数据库.
  2. Shell 1:插入到带有AUTO_INCREMENT 键.
  3. 外壳 1:SELECT LAST_INSERT_ID()，查看结果.
  4. Shell 2:插入到同一个表中.
  5. 外壳 2:SELECT LAST_INSERT_ID()，查看与 shell 1 不同的结果.
  6. 外壳 1:SELECT LAST_INSERT_ID()再次，看到前面的重复结果.

如果你仔细想想，这是唯一有意义的方法.所有支持自动递增密钥机制的数据库都必须以这种方式运行.如果结果取决于其他客户端可能同时插入的竞争条件，那么将没有可靠的方法来获取当前会话中最后插入的 ID 值.

If you think about it, this is the only way that makes sense. All databases that support auto-incrementing key mechanisms must act this way. If the result depends on a race condition with other clients possibly INSERTing concurrently, then there would be no dependable way to get the last inserted ID value in your current session.

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