Getting last record from mysql

Question

I am using mysql and facing some problem. I want to retrieve last row that is inserted.

<< Below are details >>

Below is how I created table.

create table maxID (myID varchar(4))

I inserted four values in it as below

insert into maxID values ('A001')
insert into maxID values ('A002')
insert into maxID values ('A004')
insert into maxID values ('A003')

When I execute select myID, last_insert_id() as NewID from maxID, I get output as below

myId NewID
A001   0  
A002   0  
A004   0  
A003   0    

When I tried below code,

select myId, last_insert_id() as NewID, @rowid:=@rowid+1 as myrow from maxID, (SELECT @rowid:=0) as init

I get output as below.

myId NewID  rowid
A001   0      1
A002   0      2
A004   0      3
A003   0      4

However when I use code select myId, last_insert_id() as NewID, @rowid:=@rowid+1 as myrow from maxID, (SELECT @rowid:=0) as init where @rowid = 4, I get error as Uknown column 'myrow' in where clause

When I use where @rowid=4, I don't get any data in tables.

Link to play with data

Note: Here I am using 4 just to get desired output. Later I can get this from a query (select max(rowid) from maxID)

Please suggest me what need to do if I want to see only last record i.e. A003.

Thanks for your time.

Update:

I already have millions of data in my table so I can't add new column in it as suggested below.

Answer 1

Almost done. You succeed in getting the insert order. So:

select myId, @rowid:=@rowid+1 as myrow from maxID, (SELECT @rowid:=0) as init ORDER BY myrow desc LIMIT 1;

In my console I get the following:

mysql> select myId, @rowid:=@rowid+1 as myrow from maxID, (SELECT @rowid:=0) as
init ORDER BY myrow desc LIMIT 1;
+------+-------+
| myId | myrow |
+------+-------+
| A003 |     4 |
+------+-------+
1 row in set (0.00 sec)

Demo

UPDATE

Yak is right. My solution is not deterministic. Maybe it works for small amount of records. I found tons of post abount unreliability of default sorting of a SELECT statement (here for example). Next steps:

• Under which conditions the default SELECT sorting matches the insertion order?
• Is it possible to obtain the last inserted record in a table without an incremental id or an insertion timestamp?

I know it's not an answer, but stating the problem limit the problem.

Answer 2

It seems that a SELECT is not guaranteed to return rows in any specific order (without using an ORDER BY clause, of course).

As per the SQL-92 standard (p. 373):

If an < order by clause > is not specified, then the table specified by the < cursor specification > is T and the ordering of rows in T is implementation-dependent.

Okay, MySQL is not fully SQL-92-compliant, but this is a serious hint.

Laurynas Biveinis (apparently affiliated with Percona) also states:

The order of the rows in the absence of ORDER BY clause (...) could be different due to the moon phase and that is OK.

The MySQL manual says about InnoDB:

InnoDB always orders table rows according to [a PRIMARY KEY or NOT NULL UNIQUE index] if one is present.

As far as I am concerned, I assume MySQL could also reorder rows after an OPTIMIZE TABLE or even reuse empty spaces after many deletes and inserts (I have tried to find an example of this, and have failed so far).

Given your table structure, the bottomline is, unfortunately, that so many factors could have altered the order of the rows; I see no solution to reliably determine the order they were inserted. Unless you kept all binary logs since you created the table, of course ;)

Nevertheless, you may still want to add a sequence column to your table. Existing rows would be assigned a possibly inaccurate sequence number, but at least future rows will be correctly sequenced.

ALTER TABLE maxID ADD sequence INT DEFAULT NULL;
ALTER TABLE maxID ADD INDEX(sequence);
ALTER TABLE maxID MODIFY sequence INT AUTO_INCREMENT;

http://sqlfiddle.com/#!2/63a8d/1