问题
I am using PHP and MySQL.
Goal:
Insert a new row into a table with an auto-increment id column.
While inserting this new row, I would like to copy the new inserted row's auto-increment id # into another column in the same row/entry.
Upon creation, the new entry/row should have the auto-incremented id column and another column with the same number.
My biggest concern:
I need all of this to happen correctly and reliably, even while other transactions from other connections could be taking place on the server.
So Far
I know only a little about last_insert_id()... and I am afraid of being able to use this reliably for my needs...
Will I ever run into a situation where the auto-increment id # will have already incremented (due to some other insert query from another connection perhaps) and now I will not get the correct id #? (I did not quite fully understand what it means when the last_insert_id() is given to the client on a per-connection basis).
Will last_insert_id() play nice with transactions since they become undefined when the transaction is made to rollback? (If another transaction is rolled back and then I run this script immediately after, will my script return NULL for last_insert_id()?)
I do not understand mysql_insert_id(); how to use it and whether or not it will help me.
So far, I have thought about:
- INSERT row with
columnset as last_insert_id(); - INSERT row; UPDATE
columnwith SELECT last_insert_id(); - SELECT last_insert_id(); INSERT row with
auto-increment columnandcolumnset as last_insert_id()+1
What happens when I insert a chosen value into the auto-increment column? Will the auto-increment generator start counting from the number I insert? What if I use a value that has been used before (but doesn't exist anymore) and there exists records with id # that come after that value?
Will table or row locking allow me to achieve my desired behavior?
What is the proper/correct way to do something like this?
"last_insert_id() is given to the client on a per-connection basis"
last_insert_id is client independent and will return the ID for the last inserted row from that client, therefore you do not need to worry about the case that a user on another connection transacts with the database.
I still do not fully understand what that means...
For a basic SCENARIO:
INSERT row where id = 1;
SELECT last_insert_id(); outputs 1
Person A makes a connection to the db; SELECT last_insert_id(); outputs 1.
Person B makes a connection to the db; SELECT last_insert_id(); outputs 1?
Person A INSERT another row where id = 2;
Person A SELECT last_insert_id(); outputs 2?
Person B SELECT last_insert_id(); outputs... 1 or 2??
What happens here?
And a SCENARIO that really concerns me:
Person A makes a connection with the db;
Person A SELECT last_insert_id(); outputs 1
Person A INSERT row where id = 2;
Person A SELECT last_insert_id(); outputs 2
Person B makes a connection with the db;
Person B SELECT last_insert_id(); outputs 2
Person B INSERT row where id = 3;
Person A SELECT last_insert_id(); outputs 2??
Person B SELECT last_insert_id(); outputs 3??
In this case, Person A's last_insert_id() is one count behind. If this is true, then I will not be able to use my #3 method.
Please correct my outputs for me wherever I may be wrong.
回答1:
You should check out this article regarding MySQL last_insert_id
last_insert_id is client independent and will return the ID for the last inserted row from that client, therefore you do not need to worry about the case that a user on another connection transacts with the database.
回答2:
considering you may have multiple access to your DB,
i will do:
1, just insert new row and put null into the "another column" let's call it [autoID_Copy]
2, then i can run this:
update table set autoID_Copy= autoID where autoID_Copy is null
even make it faster you may do
where timeInstered < 1 min or maybe some other filter.
hope this help.
来源：https://stackoverflow.com/questions/28485117/sql-insert-row-and-copy-inserted-auto-increment-id-to-another-column