(mysql, php) 如何在插入数据之前获取 auto_increment 字段值? [英] (mysql, php) How to get auto_increment field value before inserting data?

问题描述

我正在将图像文件上传到存储服务器.在上传之前，我应该编写文件名，其中包含 AUTOINCREMENT VALUE(例如，12345_filename.jpg).

I'm uploading image file to storage server. Before uploading I should compose filename, which contains AUTOINCREMENT VALUE in it (for example, 12345_filename.jpg).

如何在插入数据库之前获取自动增量值?

How could I get autoincrement value before inserting into DB?

我只看到一个解决方案

1. 插入空行
2. 获取它的自增值
3. 删除这一行
4. 使用 p.1 中的自动增量值插入包含真实数据的行

还有其他解决方案吗?

谢谢

推荐答案

自动增量值由数据库自身生成，插入完成后；这意味着在执行实际插入查询之前您无法获得它.

The autoincrement value is generated by the database itself, when the insertion is done ; which means you cannot get it before doing the actual insert query.

您提出的解决方案不是经常使用的解决方案——应该是:

The solution you proposed is not the one that's often used -- which would be :

• 插入一些半空数据
• 获取生成的自增值
• 使用该自动增量值进行计算
• 更新行以放置新的/完整的数据——使用前面在 update 查询的 where 子句中生成的自动增量来识别哪一行是正在更新.

• insert some half-empty data
• get the autoincrement value that's been generated
• do your calculations, using that autoincrement value
• update the row to put the new / full data in place -- using the autoincrement generated earlier in the where clause of the update query, to identify which row is being updated.

当然，为了安全起见，所有这些操作都必须在一个事务中进行(以确保全有或全无"行为)

Of course, as a security precaution, all these operations have to be made in a transaction (to ensure a "all or nothing" behavior)

作为伪代码:

begin transaction
insert into your table (half empty values);
$id = get last autoincrement id
do calculations
update set data = full data where id = $id
commit transaction

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