I'm using AUTO_INCREMENT and I would like to get that ID of inserted row so that I could update another table using ID as common field between the 2 tables.
I understood that LAST_INSERT_ID will get last ID. However, my concern is that, the database is accessed at same time by many users. Hence, there might be another process accessed the table and also inserted a new row at same time.
Does LAST_INSERT_ID return just the last ID regardless of the connection used, or only return last ID for the connection that I'm using?
Notice, I'm accessing MySQL database using connection pool in Tomcat server.
In summary, I need to insert a row in table A with auto increment, than I need to insert row in table B, which need to be linked to table A using the AUTO_INCREMENT value.
SELECT max(employeeid) FROM Employee;
The above query returns the value of employeeid of last inserted record in Employee table because employeeid is an auto increment column. This seems to be OK, but suppose two threads are executing insert operation simultaneously, there is a chance that you get wrong id of last inserted record!
Don’t worry, MySQL provides a function which returns the value of auto increment column of last inserted record.
SELECT LAST_INSERT_ID();
LAST_INSERT_ID() is always connection specific, this means even if insert operation is carried out simultaneously from different connections, it always returns the value of current connection specific operation.
So you have to first insert record in Employee table, run the above query to get the id value and use this to insert in second table.
LAST_INSERT_ID() work in context, it should be in transactions or inside user defined stored procedures or user defined functions.
LAST_INSERT_ID is connection specific. That's true, but you should be careful if you use connection pooling. This may be problematic when you perform successive INSERT IGNORE statements in a loop and the pool gives you the same connection at each iteration.
For example; Assume that you receive the same (open) connection for each of the below:
INSERT IGNORE ... some-new-id >>> LAST_INSERT_ID returns 100
INSERT IGNORE ... some-existing-id >>> LAST_INSERT_ID still returns 100 (result of the previous operation)
It is always good to check whether the INSERT operation has in fact inserted any rows before calling LAST_INSERT_ID.
LAST_INSERT_ID return the last insert id for the current session.
As long as you don't insert more than one entry with your current connection, it is valid.
Further information here: https://dba.stackexchange.com/questions/21181/is-mysqls-last-insert-id-function-guaranteed-to-be-correct
(i would link to mysql.com, but it'S currently down for me)
Related
I've had a look at the official documentation but I'm still a bit confused.
Say I have a procedure and it runs and performs an insert and then I request LAST_INSERT_ID(), am I getting the last insert id from the insert just done by my instance of the procedure running or is it the last insert id on the table by any instance/session that's called the procedure?
For example say the last inserted record ID was 4 and I called the procedure and my insert would be id 5 but my insert fails will I get 4 being returned as the last insert id or a null/0 value?
That very link to the documentation page that you gave in the question has an answer:
The ID that was generated is maintained in the server on a
per-connection basis. This means that the value returned by the
function to a given client is the first AUTO_INCREMENT value generated
for most recent statement affecting an AUTO_INCREMENT column by that
client. This value cannot be affected by other clients, even if they
generate AUTO_INCREMENT values of their own. This behavior ensures
that each client can retrieve its own ID without concern for the
activity of other clients, and without the need for locks or
transactions.
So, there is no race condition from other clients. You need to request the LAST_INSERT_ID() in the same connection as INSERT to get correct result.
As for, what happens when transaction is rolled back, it is undefined:
If the previous statement returned an error, the value of
LAST_INSERT_ID() is undefined. For transactional tables, if the
statement is rolled back due to an error, the value of
LAST_INSERT_ID() is left undefined. For manual ROLLBACK, the value of
LAST_INSERT_ID() is not restored to that before the transaction; it
remains as it was at the point of the ROLLBACK.
The documentation you linked to says:
The ID that was generated is maintained in the server on a per-connection basis. This means that the value returned by the function to a given client is the first AUTO_INCREMENT value generated for most recent statement affecting an AUTO_INCREMENT column by that client. This value cannot be affected by other clients, even if they generate AUTO_INCREMENT values of their own.
This means you can safely rely on the value returned by LAST_INSERT_ID(). It is the most recent auto incremented value generated by the same instance of the code that calls LAST_INSERT_ID(). Of course, you have to call it right after the INSERT statement you want to get the value for, it cannot return the values generated by the second most recent INSERT statement or older.
Suppose, that we have 2 databases: a and b, and tables a.test1 and b.test2.
If I need to insert a row into table a.test1, and return LAST_INSERT_ID() to insert into b.test2, will LAST_INSERT_ID() return value from another database? Is it reliable?
I didn't find anything in the manual, but ##IDENTITY depends on client session, so it should be portable between two databases. Isn't it?
LAST_INSERT_ID() always gives you the id of the row inserted by the last INSERT statement you executed on the current connection, irrespective of what table (and what database!) that row went into.
From Mysql documentation:The ID that was generated is maintained in the server on a per-connection basis. This means that the value returned by the function to a given client is the first AUTO_INCREMENT value generated for most recent statement affecting an AUTO_INCREMENT column by that client. This value cannot be affected by other clients, even if they generate AUTO_INCREMENT values of their own. This behavior ensures that each client can retrieve its own ID without concern for the activity of other clients, and without the need for locks or transactions.
Inshort Both *LAST_INSERT_ID()* and *mysql_insert_id()* work as advertised i.e.: they will retrieve the last id inserted into any table during the current session/connection.
I'm curious whether this is a possibility. I have a stored procedure which Inserts and then retrieves the last insert id. What if 2 users both use the procedure at the same time, is something like this possible?
User 1
User 2
Insert 1
Insert 2
GetsLastid 2
GetsLastid 2
Could the 2 calls of the stored procedure interlace the sequence of the insert queries? Or will one take lead?
Thank you!
That's not a problem. From the fine manual:
The ID that was generated is maintained in the server on a per-connection basis. This means that the value returned by the function to a given client is the first AUTO_INCREMENT value generated for most recent statement affecting an AUTO_INCREMENT column by that client. This value cannot be affected by other clients, even if they generate AUTO_INCREMENT values of their own.
So the last_insert_id() value is always per-session (AKA connection) and you have two sessions in play, the can't interfere with each other's last_insert_id() values.
That said, it is a good idea to grab the last_insert_id() value and store it in a variable as soon after the INSERT as possible. If you do something else that does an INSERT behind your back — say you call another procedure that has logging added two months down the road and that logging does an INSERT — you will lose the last_insert_id() value that you want.
I've got a number of tables that "share" a single auto-incrementing primary key - this is accomplished via a trigger on insert which looks like this:
FOR EACH ROW
BEGIN
INSERT INTO master (time) VALUES (NOW());
SET NEW.id = LAST_INSERT_ID();
END
This produces the PK for the just inserted row. This does, however, create the problem that I can't seem to figure out what that ID was. last_insert_id obviously returns nothing as the above statement wasn't executed on what's considered "the current connection".
Is there a way to access the most recently inserted row on a connection without an auto-incrementing primary key?
Update: As a temporary(?) measure I've removed the trigger and now generate the ID by making the insert to master within my model. Just seems like it would be nicer if I could somehow return the value that the trigger set.
The doc does say, "For stored functions and triggers that change the [LAST_INSERT_ID] value, the value is restored when the function or trigger ends, so following statements do not see a changed value."
Try a stored procedure, which can do your two INSERTS and return the assigned ID.
Or, give up on doing things the "Oracle way", drink the MySql Kool-Aid, and just use an auto-incrementing id on the table.
I am currently working on a big web project using ASP and MySQL.
When inserting into multiple tables I've been using last_update_ID(), but after some research I've found that that SQL statement isn't safe.
So. the problem:
I use two different computers, with different internet connections.
Both computers are logged onto the system I am currently building. I have made a page that prints the connection_id(), and last_update_id.
If I update any table with one of the computers the other one also gets that last_update_ID.
Both computers have the same connection_ID.
What can I do to get around this?
I don't want to (if it's not necessary) do a select statement after the first INSERT; to search for the row that I inserted, to get the correct ID of that row.
It's not my server I am using so I can't make any large changes of the database.
I guess that this problem occurs because the webpages use the same loginName & password to connect to the database, is that true?
Is there any other alternative to get the last update ID? that is totally safe..
I close every connection at the end of the asp page. but that doesn't change the connection_ID.
The connection ID is the for a few minutes even thou I open up different web pages on the server.
I believe the LAST_INSERT_ID() is correct for the current session. So each session receives it's own correct value. Either I don't understand your question or you think you have a problem but you don't.
I am not aware of any LAST_UPDATE_ID() function, on an update you can easily retrieve the updated rows by SELECTing them with the same WHERE clause (before the update)?
reference: http://dev.mysql.com/doc/refman/5.0/en/getting-unique-id.html
For LAST_INSERT_ID(), the most
recently generated ID is maintained in
the server on a per-connection basis.
It is not changed by another client.
It is not even changed if you update
another AUTO_INCREMENT column with a
nonmagic value (that is, a value that
is not NULL and not 0). Using
LAST_INSERT_ID() and AUTO_INCREMENT
columns simultaneously from multiple
clients is perfectly valid. Each
client will receive the last inserted
ID for the last statement that
client executed.
If you want to retrieve the LAST_INSERT_ID from an INSERT query with an ON DUPLICATE KEY UPDATE clause, you can also use the LAST_INSERT_ID() function to retrieve the value of the AUTO_INCREMENT column that was updated:
reference: http://dev.mysql.com/doc/refman/5.0/en/insert-on-duplicate.html
If a table contains an AUTO_INCREMENT
column and INSERT ... UPDATE inserts a
row, the LAST_INSERT_ID() function
returns the AUTO_INCREMENT value. If
the statement updates a row instead,
LAST_INSERT_ID() is not meaningful.
However, you can work around this by
using LAST_INSERT_ID(expr). Suppose
that id is the AUTO_INCREMENT column.
To make LAST_INSERT_ID() meaningful
for updates, insert rows as follows:
INSERT INTO table (a,b,c) VALUES (1,2,3)
ON DUPLICATE KEY UPDATE id=LAST_INSERT_ID(id), c=3;
Your server appears to have connection pooling turned on. What this means is that the database connection is held open after a script finishes, and the next script that comes along uses it, and thus can see any variables that were set on that connection, including LAST_INSERT_ID().
What can't happen is two script instances sharing a connection at the same time. Thus, if your server is busy enough to need to run two script instances at exactly the same time, it will simply create a second database connection, with its own separate LAST_INSERT_ID() variable, and won't interfere with the first.
In short, as long as the INSERT and the LAST_INSER_ID() request happen within the same script (and you don't somehow close the database connection between them), they're completely safe, as your script has exclusive use of that connection.