Solutions for INSERT OR UPDATE on SQL Server

Question

Assume a table structure of MyTable KEY  datafield1  datafield2       Often I want to either update an existing record  or insert a new record if it doesn t exist   Essentially   IF  key exists    run update command ELSE   run insert command   What s the best performing way to write this

User · Answer

I usually do what several of the other posters have said with regard to checking for it existing first and then doing whatever the correct path is. One thing you should remember when doing this is that the execution plan cached by sql could be nonoptimal for one path or the other. I believe the best way to do this is to call two different stored procedures.

FirstSP:
If Exists
   Call SecondSP (UpdateProc)
Else
   Call ThirdSP (InsertProc)

Now, I don't follow my own advice very often, so take it with a grain of salt.

User · Answer

See my detailed answer to a very similar previous question   Beau Crawford s is a good way in SQL 2005 and below  though if you re granting rep it should go to the first guy to SO it  The only problem is that for inserts it s still two IO operations   MS Sql2008 introduces merge from the SQL 2003 standard   merge tablename with HOLDLOCK  as target using  values   new value    different value        as source  field1  field2      on target idfield   7 when matched then     update     set field1   source field1          field2   source field2              when not matched then     insert   idfield  field1  field2            values   7   source field1  source field2          Now it s really just one IO operation  but awful code  -

User · Answer

I had tried below solution and it works for me  when concurrent request for insert statement occurs   begin tran if exists  select   from table with  updlock serializable  where key    key  begin    update table set        where key    key end else begin    insert table  key          values   key       end commit tran

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CREATE TABLE ApplicationsDesSocietes      id                   INT IDENTITY 0 1     NOT NULL     applicationId        INT                  NOT NULL     societeId            INT                  NOT NULL     suppression          BIT                  NULL     CONSTRAINT PK APPLICATIONSDESSOCIETES PRIMARY KEY  id    GO --    DECLARE  applicationId INT   81   societeId INT   43   suppression BIT   0  MERGE dbo ApplicationsDesSocietes WITH  HOLDLOCK  AS target --set the SOURCE table one row USING  VALUES   applicationId   societeId   suppression       AS source  applicationId  societeId  suppression      --here goes the ON join condition     ON target applicationId   source applicationId and target societeId   source societeId WHEN MATCHED THEN     UPDATE     --place your list of SET here     SET target suppression   source suppression WHEN NOT MATCHED THEN     --insert a new line with the SOURCE table one row     INSERT  applicationId  societeId  suppression      VALUES  source applicationId  source societeId  source suppression   GO   Replace table and field names by whatever you need  Take care of the using ON condition  Then set the appropriate value  and type  for the variables on the DECLARE line   Cheers

User · Answer

Assuming that you want to insert update single row  most optimal approach is to use SQL Server s REPEATABLE READ transaction isolation level  SET TRANSACTION ISOLATION LEVEL REPEATABLE READ  BEGIN TRANSACTION      IF  EXISTS  SELECT   FROM myTable WHERE key  key          UPDATE myTable SET             WHERE key  key     ELSE         INSERT INTO myTable  key               VALUES   key        COMMIT TRANSACTION  This isolation level will prevent block subsequent repeatable read transactions from accessing same row  WHERE key  key  while currently running transaction is open  On the other hand  operations on another row won t be blocked  WHERE key  key2

User · Answer

You can use MERGE Statement  This statement is used to insert data if not exist or update if does exist   MERGE INTO Employee AS e using EmployeeUpdate AS eu ON e EmployeeID   eu EmployeeID

User · Answer

In SQL Server 2008 you can use the MERGE statement

User · Answer

You can use this query  Work in all SQL Server editions  It s simple  and clear  But you need use 2 queries  You can use if you can t use MERGE      BEGIN TRAN      UPDATE table     SET Id    ID  Description    Description     WHERE Id    Id      INSERT INTO table Id  Description      SELECT  Id   Description     WHERE NOT EXISTS  SELECT NULL FROM table WHERE Id    Id       COMMIT TRAN   NOTE  Please explain answer negatives

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IF EXISTS  SELECT   FROM  Table  WHERE ID   rowID  UPDATE  Table  SET propertyOne   propOne  property2       ELSE INSERT INTO  Table   propOne  propTwo          Edit        Alas  even to my own detriment  I must admit the solutions that do this without a select seem to be better since they accomplish the task with one less step

User · Answer

Do a select  if you get a result  update it  if not  create it

User · Answer

That depends on the usage pattern  One has to look at the usage big picture without getting lost in the details  For example  if the usage pattern is 99  updates after the record has been created  then the  UPSERT  is the best solution   After the first insert  hit   it will be all single statement updates  no ifs or buts  The  where  condition on the insert is necessary otherwise it will insert duplicates  and you don t want to deal with locking   UPDATE  lt tableName gt  SET  lt field gt   field WHERE key  key   IF   ROWCOUNT   0 BEGIN    INSERT INTO  lt tableName gt   field     SELECT  field    WHERE NOT EXISTS  select   from tableName where key    key   END

User · Answer

If you want to UPSERT more than one record at a time you can use the ANSI SQL 2003 DML statement MERGE   MERGE INTO table name WITH  HOLDLOCK  USING table name ON  condition  WHEN MATCHED THEN UPDATE SET column1   value1    column2   value2      WHEN NOT MATCHED THEN INSERT  column1    column2       VALUES  value1    value2         Check out Mimicking MERGE Statement in SQL Server 2005

User · Answer

If you use ADO NET  the DataAdapter handles this   If you want to handle it yourself  this is the way   Make sure there is a primary key constraint on your key column   Then you    Do the update If the update fails because a record with the key already exists  do the insert  If the update does not fail  you are finished    You can also do it the other way round  i e  do the insert first  and do the update if the insert fails  Normally the first way is better  because updates are done more often than inserts

User · Answer

don t forget about transactions  Performance is good  but simple  IF EXISTS    approach is very dangerous  When multiple threads will try to perform Insert-or-update you can easily  get primary key violation   Solutions provided by  Beau Crawford  amp   Esteban show general idea but error-prone   To avoid deadlocks and PK violations you can use something like this     begin tran if exists  select   from table with  updlock serializable  where key    key  begin    update table set        where key    key end else begin    insert into table  key          values   key       end commit tran   or  begin tran    update table with  serializable  set        where key    key     if   rowcount   0    begin       insert into table  key       values   key        end commit tran

User · Answer

Does the race conditions really matter if you first try an update followed by an insert   Lets say you have two threads that want to set a value for key key   Thread 1  value   1 Thread 2  value   2    Example race condition scenario   key is not defined Thread 1 fails with update Thread 2 fails with update Exactly one of thread 1 or thread 2 succeeds with insert  E g  thread 1 The other thread fails with insert  with error duplicate key  - thread 2    Result  The  first  of the two treads to insert  decides value  Wanted result  The last of the 2 threads to write data  update or insert  should decide value    But  in a multithreaded environment  the OS scheduler decides on the order of the thread execution - in the above scenario  where we have this race condition  it was the OS that decided on the sequence of execution  Ie  It is wrong to say that  thread 1  or  thread 2  was  first  from a system viewpoint   When the time of execution is so close for thread 1 and thread 2  the outcome of the race condition doesn t matter  The only requirement should be that one of the threads should define the resulting value   For the implementation  If update followed by insert results in error  duplicate key   this should be treated as success    Also  one should of course never assume that value in the database is the same as the value you wrote last

User · Answer

Do an UPSERT    UPDATE MyTable SET FieldA  FieldA WHERE Key  Key  IF   ROWCOUNT   0    INSERT INTO MyTable  FieldA  VALUES   FieldA    http   en wikipedia org wiki Upsert

User · Answer

Although its pretty late to comment on this I want to add a more complete example using MERGE   Such Insert Update statements are usually called  Upsert  statements and can be implemented using MERGE in SQL Server   A very good example is given here  http   weblogs sqlteam com dang archive 2009 01 31 UPSERT-Race-Condition-With-MERGE aspx  The above explains locking and concurrency scenarios as well   I will be quoting the same for reference   ALTER PROCEDURE dbo Merge Foo2        ID int AS  SET NOCOUNT  XACT ABORT ON   MERGE dbo Foo2 WITH  HOLDLOCK  AS f USING  SELECT  ID AS ID  AS new foo       ON f ID   new foo ID WHEN MATCHED THEN     UPDATE             SET f UpdateSpid     SPID              UpdateTime   SYSDATETIME   WHEN NOT MATCHED THEN     INSERT                     ID              InsertSpid              InsertTime             VALUES                     new foo ID                SPID              SYSDATETIME             RETURN   ERROR

User · Answer

Many people will suggest you use MERGE  but I caution you against it  By default  it doesn t protect you from concurrency and race conditions any more than multiple statements  and it introduces other dangers   Use Caution with SQL Server s MERGE Statement  Even with this  quot simpler quot  syntax available  I still prefer this approach  error handling omitted for brevity   BEGIN TRANSACTION   UPDATE dbo table WITH  UPDLOCK  SERIALIZABLE     SET     WHERE PK    PK   IF   ROWCOUNT   0 BEGIN   INSERT dbo table PK       SELECT  PK       END  COMMIT TRANSACTION    Please stop using this UPSERT anti-pattern  A lot of folks will suggest this way  SET TRANSACTION ISOLATION LEVEL SERIALIZABLE   BEGIN TRANSACTION   IF EXISTS  SELECT 1 FROM dbo table WHERE PK    PK  BEGIN   UPDATE     END ELSE BEGIN   INSERT     END COMMIT TRANSACTION   But all this accomplishes is ensuring you may need to read the table twice to locate the row s  to be updated  In the first sample  you will only ever need to locate the row s  once   In both cases  if no rows are found from the initial read  an insert occurs   Others will suggest this way  BEGIN TRY   INSERT     END TRY BEGIN CATCH   IF ERROR NUMBER     2627     UPDATE     END CATCH  However  this is problematic if for no other reason than letting SQL Server catch exceptions that you could have prevented in the first place is much more expensive  except in the rare scenario where almost every insert fails  I prove as much here   Checking for potential constraint violations before entering TRY CATCH Performance impact of different error handling techniques

User · Answer

If going the UPDATE if-no-rows-updated then INSERT route  consider doing the INSERT first to prevent a race condition  assuming no intervening DELETE   INSERT INTO MyTable  Key  FieldA     SELECT  Key   FieldA    WHERE NOT EXISTS             SELECT          FROM  MyTable        WHERE Key    Key      IF   ROWCOUNT   0 BEGIN    UPDATE MyTable    SET FieldA  FieldA    WHERE Key  Key    IF   ROWCOUNT   0        record was deleted  consider looping to re-run the INSERT  or RAISERROR     END   Apart from avoiding a race condition  if in most cases the record will already exist then this will cause the INSERT to fail  wasting CPU   Using MERGE probably preferable for SQL2008 onwards

User · Answer

Before everyone jumps to HOLDLOCK-s out of fear from these nafarious users running your sprocs directly  -  let me point out that you have to guarantee uniqueness of new PK-s by design  identity keys  sequence generators in Oracle  unique indexes for external ID-s  queries covered by indexes   That s the alpha and omega of the issue  If you don t have that  no HOLDLOCK-s of the universe are going to save you and if you do have that then you don t need anything beyond UPDLOCK on the first select  or to use update first    Sprocs normally run under very controlled conditions and with the assumption of a trusted caller  mid tier   Meaning that if a simple upsert pattern  update insert or merge  ever sees duplicate PK that means a bug in your mid-tier or table design and it s good that SQL will yell a fault in such case and reject the record  Placing a HOLDLOCK in this case equals eating exceptions and taking in potentially faulty data  besides reducing your perf   Having said that  Using MERGE  or UPDATE then INSERT is easier on your server and less error prone since you don t have to remember to add  UPDLOCK  to first select  Also  if you are doing inserts updates in small batches you need to know your data in order to decide whether a transaction is appropriate or not  It it s just a collection of unrelated records then additional  enveloping  transaction will be detrimental

User · Answer

MS SQL Server 2008 introduces the MERGE statement  which I believe is part of the SQL 2003 standard   As many have shown it is not a big deal to handle one row cases  but when dealing with large datasets  one needs a cursor  with all the performance problems that come along   The MERGE statement will be much welcomed addition when dealing with large datasets

User · Answer

MS SQL Server 2008 introduces the MERGE statement  which I believe is part of the SQL 2003 standard   As many have shown it is not a big deal to handle one row cases  but when dealing with large datasets  one needs a cursor  with all the performance problems that come along   The MERGE statement will be much welcomed addition when dealing with large datasets

User · Answer

Doing an if exists     else     involves doing two requests minimum  one to check  one to take action   The following approach requires only one where the record exists  two if an insert is required   DECLARE  RowExists bit SET  RowExists   0 UPDATE MyTable SET DataField1    xxx    RowExists   1 WHERE Key   123 IF  RowExists   0   INSERT INTO MyTable  Key  DataField1  VALUES  123   xxx

User · Answer

See my detailed answer to a very similar previous question   Beau Crawford s is a good way in SQL 2005 and below  though if you re granting rep it should go to the first guy to SO it  The only problem is that for inserts it s still two IO operations   MS Sql2008 introduces merge from the SQL 2003 standard   merge tablename with HOLDLOCK  as target using  values   new value    different value        as source  field1  field2      on target idfield   7 when matched then     update     set field1   source field1          field2   source field2              when not matched then     insert   idfield  field1  field2            values   7   source field1  source field2          Now it s really just one IO operation  but awful code  -

[sql] Solutions for INSERT OR UPDATE on SQL Server

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