MySQL Assuming autoincremented IDs based on multi value insert and first id - mysql

Just wanted to runt this by someone who knows more MySQL than myself
I perform a MySQL insert where I insert say 10 rows in one query. Then when you get MySQL's last insert id, it gives you the ID of the first inserted ID.
Is it safe to assume that the other IDs are consecutively the insert_id - insert_id+9? or is there any possible way this could not turn out to be the case?
Thanks

Yes, there is a possibility this will not always be the case.
With innodb_autoinc_lock_mode = 2, the rows inserted by a single INSERT statement can be assigned AUTO_INCREMENT values that are not consecutive (when concurrent INSERT statements are running.)
http://dev.mysql.com/doc/refman/5.1/en/innodb-auto-increment-handling.html

Related

MySQL LAST_INSERT_ID() question potential

If i have insert query for example:
INSERT INTO user(username) VALUES('admin');
And then get the id of the inserted record with
LAST_INSERT_ID();
Looks find but what happens if between the insert and LAST_INSERT_ID() another insert is executed.
How MySQL knows to return the correct id (for the first or second insert) since no parameter is passed to LAST_INSERT_ID();
Is it save to use this function?
Thanks
I'm supposing that you mean what happen if i'm connected to the MySQL server and executing an INSERT but others are also doing insert, like updating a table on a website while client are currently using it.
If you go take a look at the documentation https://dev.mysql.com/doc/refman/8.0/en/information-functions.html there is a point that answers your questions:
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.
This should be the same in MariaDB.
As discussed in the comment, you are wondering if you can use this in a php PDO environment. If you mean to use this directly from the database, it's a no, you won't be able to have the last inserted ID because you won't have the same client connection as PDO. If you want to use it directly from PDO please use the specific PDO function: http://php.net/manual/fr/pdo.lastinsertid.php , this should allow to do what you want.
If you insert multiple rows into a table using a single INSERT query, the LAST_INSERT_ID function returns the last insert id of the first row.
i.e
If your table id has 3 as column value and you will insert 4 rows in a single query then LAST_INSERT_ID will give you 4 instead of 7
If you insert 4 rows in 4 different insert query then LAST_INSERT_ID will give you 7
last_insert_id( ) Or mysqli_insert_id( ) will always return the id of last or most recent query. And also be noted that id field must have AUTO_INCREMENT enabled.
It doesn't give you the freedom to choose any specific table. Or you can't have id which is generated from your previous query.
So, from this point it serves a very small purpose. Only the last id, it doesn't matter which table.
To get last id from any specific table this query would be helpful : "SELECT id FROM table_name ORDER BY id DESC LIMIT 1"

How to get inserted IDs of multiple rows on one INSERT?

I want to insert multiple rows into a table, using a single INSERT statement. This is no problem, since SQL offers the option to provide multiple rows as parameter for a single INSERT statement. Now, those rows contain an ID field that is incremented automatically, i.e. its value is set by the database, not by my code.
As a result, I would like to get the ID values of the inserted rows. My basic question is: How do I do that for MariaDB / MySQL?
As it turns out, this is pretty simple, e.g. in PostgreSQL, as PostgreSQL has the RETURNING clause for INSERT which returns the desired values for one or even for multiple rows. This is exactly what I want and it works.
Unfortunately, neither MariaDB nor MySQL have PostgreSQL's RETURNING clause, so I need to fallback to something such as LAST_INSERT_ID(), but this only returns the ID of the single last inserted row, even if multiple rows were inserted using a single INSERT. How do I get all the ID values?
My code currently looks like this:
INSERT INTO mytable
(foo, bar)
VALUES
('fooA', 'barA'),
('fooB', 'barB');
SELECT LAST_INSERT_ID() AS id;
How can I solve this issue in a way that works even with concurrent writes?
(And no, it's not an option to change to a UUID field, or something like this; the auto-increment field is given, and can not be changed.)
MySQL & MariaDB have the LAST_INSERT_ID() function, and it returns the id generated by the most recent INSERT statement in your current session.
But when your INSERT statement inserts multiple rows, LAST_INSERT_ID() returns the first id in the set generated.
In such a batch of multiple rows, you can rely on the subsequent id's being consecutive. The MySQL JDBC driver depends on this, for example.
If the rows you insert include a mix of NULL and non-NULL values for the id column, you have a risk of messing up this assumption. The JDBC driver returns the wrong values for the set of generated id's.
As stated in the comments, you can capture the inserted IDs (SQL Server):
use tempdb
create table test (
id int identity(1,1) primary key,
t varchar(10) null
)
create table ids (
i int not null
)
insert test(t)
output inserted.id into ids
values (null), (null), (null)
select *
from test
select *
from ids

How to insert to two tables with one query if one table is a junction table?

How can I INSERT values to two tables using only one query? I am using MySQL. One of the tables I want to insert to is a many-to-many relationship table. Please see my example below:
I recently added the many-to-many relationship tables. When I insert on the news, I type the following script:
INSERT INTO news (title, reporter_id)
VALUES ('Some Title', 15);
How can I have one query an be able to insert to two tables? Per MySQL insert documentation, seems like I can do query like
INSERT INTO tbl_name (a,b,c) VALUES(1,2,3),(4,5,6),(7,8,9);
The problem is, I dont know my news_id until I execute my first insert. Should I just have two insert statements or is there a better way? Thanks for your help!
As mentioned by Uueerdo in the comments, you can use an AFTER INSERT trigger and access the generated ID with NEW.id. However - if you want to keep that logic in your application layer, you can copy the data from the first table to the second after your bulk insert with:
start transaction;
insert into news(title, reporter_id) values
('title2', 2),
('title3', 3);
insert into junctions(news_id, reporter_id)
select id, reporter_id
from news
where id >= last_insert_id()
order by id asc
limit 2;
commit;
This works for InnoDB if the innodb_autoinc_lock_mode is set to 0 or 1, because the generated IDs are guaranteed to be consecutive.
With innodb_autoinc_lock_mode set to 0 (“traditional”) or 1 (“consecutive”), the auto-increment values generated by any given statement are consecutive, without gaps, because the table-level AUTO-INC lock is held until the end of the statement, and only one such statement can execute at a time.
AUTO_INCREMENT Handling in InnoDB
LAST_INSERT_ID() will return the generated ID of the first inserted row.
If you insert multiple rows using a single INSERT statement, LAST_INSERT_ID() returns the value generated for the first inserted row only.
Information Functions - LAST_INSERT_ID()
You know the first generated ID. You know the number of inserted rows. So you know which rows to copy.
Demo: http://rextester.com/UEN69961

How to detect inserted ids on "insert ignore" statement?

Now,do nothing when "on duplicate key update".
So,
INSERT IGNORE INTO t1 c1 VALUES(...,...,...);
The last_insert_id is only one id at most.
Then how to detect multi inserted ids on "insert ignore" statement?
Using LAST_INSERT_ID()
There is no way that I'm aware of that a regular bulk INSERT can return more than one LAST_INSERT_ID(). It will always return the ID of the first record inserted for that bulk INSERT statement.
You can view the documentation on it which explains that here
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.
Emphasis on the first AUTO_INCREMENT value generated for most recent statement affecting an AUTO_INCREMENT column. So as described the first successful row inserted via a bulk INSERT will be the return value of LAST_INSERT_ID().
Using LAST_INSERT_ID() and ROW_COUNT() with InnoDB
There is an alternate solution as posted by Dag Sondre Hansen here which may suit your needs. It does presume your tables/database use InnoDB though.
If you are using InnoDB on a recent version of MySQL, you can get the
list of IDs using LAST_INSERT_ID() and ROW_COUNT().
InnoDB guarantees sequential numbers for AUTO INCREMENT when doing
bulk inserts, provided innodb_autoinc_lock_mode is set to 0
(traditional) or 1 (consecutive). Consequently you can get the first
ID from LAST_INSERT_ID() and the last by adding ROW_COUNT()-1.
Just make sure you do this on the same connection, directly after your INSERT statement or you won't get the results you're expecting.

How to insert two associated records into two tables?

I'd like to insert two associated records into two tables. One record is associated with another record by a foreign key.
e.g. I have two records:
product (productid,product_name,category_id)
category (category_id,category_name)
But the category_id is auto_increment. So I don't know its value until I insert it into the category table. So here I have to invoke three sql queries, one is to insert record into category table, second is retrieval the category_id, the last sql query is to insert record into product table.
Overall, it seems the performance will not be good because of executing three sql queries. I just want to know is there any best practice for this scenario ? Thanks
Jeff Zhang
Check here how you can get the last inserted unique id
When a new AUTO_INCREMENT value has
been generated, you can also obtain it
by executing a SELECT LAST_INSERT_ID()
statement with mysql_query() and
retrieving the value from the result
set returned by the statement.
Also note that
For LAST_INSERT_ID(), the most
recently generated ID is maintained in
the server on a per-connection basis
You don't have to invoke SQL to see the inserted autoincrement value, you can use last_insert_id function.