SQL Server: How to get the Last Inserted Identity value. What is the fastest way?

Hello friends,


Very often after inserting a row in a table it is necessary to know what is the id of the row just inserted.

We have various methods but what is the fastest?

Today we take a watch to this question!

Enjoy the reading!

 

As usually for maximum clarity we will proceed with an example using our standard table.

It has an identity column called ID 


The classic way!

 SELECT MAX(ID) FROM ORDTES

 


(1 riga interessata)

Tabella 'OrdTes'. Conteggio analisi 1, letture logiche 2, letture fisiche 0, letture read-ahead 0, letture logiche LOB 0, letture fisiche LOB 0, letture read-ahead LOB 0.

 

(1 riga interessata)


 

  SELECT TOP 1 ID FROM ORDTES ORDER BY ID DESC

 
 
 

 

(1 riga interessata)

Tabella 'OrdTes'. Conteggio analisi 1, letture logiche 2, letture fisiche 0, letture read-ahead 0, letture logiche LOB 0, letture fisiche LOB 0, letture read-ahead LOB 0.

   



 

We can note that with these first two methods we access the table albeit through the index that contains the ID column. It is fast because since the index is sorted by ID it is sufficient to read the first line.

There also other ways which we will now analyze.

First you should know what is a scope.

 

What is The Scope

 

A scope is simply a module that contain T-SQL code.  A stored procedure, a trigger, a function, or batch in module.

Therefore, if two T-SQL statements are in the same stored procedure, function, or batch, they are in the same scope

 

 

There are three  similar functions but each one has its own particularity.

The diagram below should summarize well..

 

 
 
 

Talking about @@IDENTITY, SCOPE_IDENTITY() and IDENT_CURRENT(‘tablename’)

 

@@IDENTITY

The @@identity function returns the last identity value with this characteristics.

  • For the current active connection (session),
  • regardless of the table that produced the value,
  • regardless of the scope of the statement that produced the value.

 

SCOPE_IDENTITY()

It returns the last IDENTITY value:

  • For the current active connection (session),
  • regardless of the table that produced the value.
  • and by a statement in the same scope,

so SCOPE_IDENTITY(), unlike @@IDENTITY, will return the last identity value created in the current session, but it will also limit it to your current scope as well.

In other words, it will return the last identity value that you explicitly created, rather than any identity that was created by a trigger or a user defined function.

 

The Any scope problem


So there is a problem due to of the “regardless of the scope”: If you have a trigger on a table that causes an identity to be created in another table because you will get the identity that was created last, even if it was the trigger that created it.

Infact assuming that both T1 and T2 have identity columns, @@IDENTITY and SCOPE_IDENTITY return different values at the end of an INSERT statement on T1. 

While @@IDENTITY returns the last identity column value inserted across any scope in the current session. This is the value inserted in T2. SCOPE_IDENTITY() returns the IDENTITY value inserted in T1. This was the last insert that occurred in the same scope. 

The SCOPE_IDENTITY() function returns the null value if the function is invoked before any INSERT statements into an identity column occur in the scope.

 

Finally we have the

IDENT_CURRENT(‘tablename’)

It returns the last IDENTITY value

  • produced in a table,
  • regardless of the connection that created the value, and
  • regardless of the scope of the statement that produced the value.

IDENT_CURRENT is not limited by scope and session; it is limited to a specified table. IDENT_CURRENT returns the identity value generated for a specific table in any session and any scope.

 

Note that: Failed statements and transactions can change the current identity for a table and create gaps in the identity column values. The identity value is never rolled back even though the transaction that tried to insert the value into the table is not committed. For example, if an INSERT statement fails because of an IGNORE_DUP_KEY violation, the current identity value for the table is still incremented.

 

 

Finally speaking of performances.

 


 

@@IDENTITY, SCOPE_IDENTITY and IDENT_CURRENT are 5 times fastest that quering that table directly!

 

 

That's all for Today!
Luca











Previous post:SQL Server, MrbMiner the new malware that infects SQL Server!

 

Comments

  1. James ZicrovFebruary 22, 2021 at 12:18 AM

    Thank you so much for providing information about most useful and popular aspects of SQL and its functions such as Insert,Update and Delete.

    SQL Server Load Rest API

    ReplyDelete

Post a Comment

I Post più popolari

SQL Server, execution plan and the lazy spool (clearly explained)

Image
Hi Guys, Welcome back! In one of the last posts we talked about Table Spool . We had explained what Spool are for by telling the somewhat curious story of the halloween problem . Here we specifically talked about a type of spool called Eager Spool   You can look to the execution plan below where the eager Spool is used to avoid the halloween problem in classic query of the "salary increase".. i suggest Well, if the story of the eager spool intrigued you, today instead we will speak about another type of Spool, the Lazy Spool . The Lazy spool Let's take a small step back. So, what is a Spool operation?  As we have already understood a spool operation is simply a temporary storage of data . Data are read from a source table and stored inside a worktable in the Tempdb database . While an Eager Spool is used to prevent the Halloween problem, the Lazy Spool is instead used to store data that will later be needed again when running a query . So, when a Lazy spool is used?  ...
Read more

SQL Server, datetime vs. datetime2

Image
Hi guys, This time, in this post we will speak about datetime and datetime2 datatypes. We will talk about the pros and cons. We will talk about all the differences between the two types of data. Write me in the comments which type of data do you prefer between the two. Enjoy the reading!     Datetime Vs. Datetime2 First of all, it must be said that the datatype datetime is certainly the best known native format for storing a date in SQL Server. However, Microsoft has also been introducing a new type of data for many years now, also used to manage dates. It is in fact from SQL server 2008 that it is present in datetime2 data type. This "new" type of data was born primarily to have higher accuracy . Let's in fact talk about ... precision ! Datetime Certainly the datetime data type is not very precise and certainly there are many cases in which its precision is simply not sufficient. Let's see it with an example. Open the SQL Management studio (SSMS) and write the fo...
Read more

La clausola NOLOCK. Approfondiamo e facciamo chiarezza!

Image
Ehi ragazzi! La domanda è di quelle importanti! Siete pronti per scoprire tutto ma proprio tutto sulla clausola NOLOCK?   Se la riposta è si, allora seguitemi! Oggi ne spiegheremo il funzionamento in maniera approfondita. Faremo una introduzione al concetto di tipi di LOCK Ed infine vedremo come mai una SELECT ne può bloccare un'altra. Non vi nascondo che il motivo di questo articolo è fare chiarezza. Su questo argomento si sentono spesso affermazioni “curiose” ma tra le tante questa è la prima: “ uso la SELECT con l’opzione WITH(LOCK) così non blocco le altre tabelle ”.   Ma, è proprio vero quanto affermato? Beh oggi facciamo il punto!   Buona lettura!     La clausola NOLOCK Diciamo subito per iniziare che cos’è la NOLOCK. NOLOCK è il nome di una clausola che è possibile specificare all’interno di uno statement di tipo SELECT utilizzando la seguente sintassi: SELECT * FROM TABELLA WITH (NOLOCK) Si noti che non possiamo ...
Read more