Is there a way to SELECT and UPDATE rows at the same time?

Question

I\'d like to update a set of rows based on a simple criteria and get the list of PKs that were changed. I thought I could just do something like this but am worried about po

Answer 1

Edit: my bad, you wanted the select to show results after the update, not update from a select.

Have you tried a sub-select?

update mytable set mydate = sysdate 
where mydate in (select mydate from mytable where mydate is null);

Answer 2

I have faced the same issue; I have to update the credit amount, and have to get modified time, along with credit details from DB. It is basically

SYNCHRONOUSLY/ATOMICALLY perform (UPDATE then GET) in MYSQL

I have tried many options and found one that solved my issue.

1) OPTION_1 SELECT FOR UPDATE

This is maintaining the lock till update (SYNC from GET to UPDATE), but i need lock after update till the GET.

2) OPTION_2 Stored procedure

Stored procedure will not execute synchronously like redis lua, So there also we need sync code to perform that.

3) OPTION_3 Transaction

I have used JPA entityManager like below, thought that before commit no one can update, and before commit i will get the updated object along with modified time (from DB). But i didn't get the latest object. Only commit i got the latest.

    try {
        entityManager.getTransaction().begin();
        //entityManager.persist(object);
        int upsert = entityManager.createNativeQuery(
        "update com.bill.Credit c set c.balance = c.balance - ?1
          where c.accountId = ?2 and c.balance >= ?1").executeUpdate(); 
             //c.balance >= ? for limit check
        Credit newCredit = entityManager.find(Credit.class, "id");
        entityManager.refresh(newCredit); //SHOULD GET LATEST BUT NOT
        entityManager.getTransaction().commit();
    } finally {     
        entityManager.unwrap(Session.class).close();
    } 

4) OPTION_4 LOCK solved the issue, so before update i acquired the lock; then after GET i have released the lock.

private Object getLock(final EntityManager entityManager, final String Id){

    entityManager.getTransaction().begin();
    Object obj_acquire = entityManager.createNativeQuery("SELECT GET_LOCK('" + Id + "', 10)").getSingleResult();
    entityManager.getTransaction().commit();
    return obj_acquire;
}


private Object releaseLock(final EntityManager entityManager, final String Id){

    entityManager.getTransaction().begin();
    Object obj_release = entityManager.createNativeQuery("SELECT RELEASE_LOCK('" + Id + "')").getSingleResult();
    entityManager.getTransaction().commit();
    return obj_release;
}

Answer 3

in SQL 2008 a new TSQL statement "MERGE" is introduced which performs insert, update, or delete operations on a target table based on the results of a join with a source table. You can synchronize two tables by inserting, updating, or deleting rows in one table based on differences found in the other table.

http://blogs.msdn.com/ajaiman/archive/2008/06/25/tsql-merge-statement-sql-2008.aspx http://msdn.microsoft.com/en-us/library/bb510625.aspx

Answer 4

Consider looking at the OUTPUT clause:

USE AdventureWorks2012;  
GO  

DECLARE @MyTableVar table(  
    EmpID int NOT NULL,  
    OldVacationHours int,  
    NewVacationHours int,  
    ModifiedDate datetime);  

UPDATE TOP (10) HumanResources.Employee  
SET VacationHours = VacationHours * 1.25,  
    ModifiedDate = GETDATE()   
OUTPUT inserted.BusinessEntityID,  
       deleted.VacationHours,  
       inserted.VacationHours,  
       inserted.ModifiedDate  
INTO @MyTableVar;  

--Display the result set of the table variable.  
SELECT EmpID, OldVacationHours, NewVacationHours, ModifiedDate  
FROM @MyTableVar;  
GO  
--Display the result set of the table.  
SELECT TOP (10) BusinessEntityID, VacationHours, ModifiedDate  
FROM HumanResources.Employee;  
GO 

Answer 5

if it's inside the transaction, the database locking system will take care of concurrency issues. of course, if you use one (the mssql default is that it uses lock, so it states if you don't override that)

Answer 6

Many years later...

The accepted answer of using the OUTPUT clause is good. I had to dig up the actual syntax, so here it is:

DECLARE @UpdatedIDs table (ID int)
UPDATE 
    Table1 
SET 
    AlertDate = getutcdate() 
OUTPUT
    inserted.Id
INTO
    @UpdatedIDs
WHERE 
    AlertDate IS NULL;

ADDED SEP 14, 2015:

"Can I use a scalar variable instead of a table variable?" one may ask... Sorry, but no you can't. You'll have to SELECT @SomeID = ID from @UpdatedIDs if you need a single ID.