如何防止ID错误 [英] how to prevent from getting wrong ID

问题描述

database = mysql language = php

我是编程程序，工作方式如下

PC1 = computer1

步骤

1.PC1从自动递增中插入数据，新ID。

2.PC1选择最后一个ID

一切正常，但...

当你的代码被同一个mili-sec上的许多计算机使用时的问题。
例如

1. PC1插入数据，自动递增新ID

2.PC2插入数据，自动增加新ID

3.PC1选择最后一个ID <-------错误

4PC2选择最后一个ID

如何配置数据库或修改PHP代码以防止出现这种情况，谢谢。 / p>

解决方案

您应该使用 mysql_insert_id （或者您正在使用的API的等效调用）来获取最后插入的行的ID。

我想象现在你正在这样做：

  SELECT MAX（id）FROM yourtable 
  

这不会工作，除非你使用交易。但是使用函数 mysql_insert_id 是更好的方法。

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文档也有一些警告和一些注释，您应该阅读：

注意：mysql_insert_id将本机MySQL C API函数mysql_insert_id（）的返回类型转换为long类型（在PHP中命名为int）。如果AUTO_INCREMENT列的列类型为BIGINT（64位），则转换可能会导致值不正确。

注意：因为mysql_insert_id（）会对最后执行的查询执行操作，因此会在SQL查询中使用内部MySQL SQL函数LAST_INSERT_ID ，请务必在生成该值的查询后立即调用mysql_insert_id（）。

注意：MySQL SQL函数LAST_INSERT_ID ）始终包含最近生成的AUTO_INCREMENT值，并且在查询之间不会重置。

database= mysql language=php

I am coding program to work like this

PC1 =computer1

step

1.PC1 insert data ,new ID from Auto-increment.

2.PC1 select last ID

everything work fine but..

The problem when your code is used by many computers at the same mili-sec. For example

1. PC1insert data,Auto-increment new ID

2.PC2 insert data ,Auto-increment new ID

3.PC1 select last ID <-------Wrong

4PC2 select last ID

How to config database or modify php code to prevent this , thankyou.

解决方案

You should use mysql_insert_id (or the equivalent call for the API you are using) to get the ID of the last inserted row.

I imagine that now you are doing this:

SELECT MAX(id) FROM yourtable

This won't work unless you use transactions. But using the function mysql_insert_id is the better way.

---

In the documenation there is also a caution and some notes that you should read:

Caution: mysql_insert_id() will convert the return type of the native MySQL C API function mysql_insert_id() to a type of long (named int in PHP). If your AUTO_INCREMENT column has a column type of BIGINT (64 bits) the conversion may result in an incorrect value. Instead, use the internal MySQL SQL function LAST_INSERT_ID() in an SQL query.

Note: Because mysql_insert_id() acts on the last performed query, be sure to call mysql_insert_id() immediately after the query that generates the value.

Note: The value of the MySQL SQL function LAST_INSERT_ID() always contains the most recently generated AUTO_INCREMENT value, and is not reset between queries.

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