Question

UPDATE dbo.A  
  SET StatusCode = 'booked' 
   , UpdateDate = GETDATE()
 OUTPUT INSERTED.id INTO @TableVar
 WHERE id = ( 
     SELECT TOP 1 wq.id
     FROM dbo.A AS wq
     WHERE wq.statusCode = 'Claimed' and wq.id = 2

)

i need update table A which id equal 2 and statusCode equals ‘Claimed’ update to ‘booked’

is it threadsafe?
tks

Answer 1

You can improve concurrency safety by adding with (updlock, holdlock) to the subquery:

FROM dbo.A AS wq with (updlock, holdlock)

An equivalent would be to wrap the statement in a repeatable read transaction:

REPEATABLE READ
Specifies that statements cannot read data that has been modified but not yet 
committed by other transactions and that no other transactions can modify data 
that has been read by the current transaction until the current transaction 
completes.

This looks like:

set transaction isolation level repeatable read
start transaction
... your query here ...
commit transaction