Question

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.

Answer 1

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.

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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.