4D v11 SQL Release 2 introduces commands to lock the entire selection of records for subsequent queries:

SET QUERY AND LOCK

Testing for success of these commands is a bit more complex than it might seem. Remember:

• Locks records for the duration of the current transaction.


• If a query fails (did not lock all records) the current selection will be emptied.
  
  
  
  • However, the current selection may also be empty because the query did not return any results.
  
  
  
  


• If a query fails, 4D creates a locked records set ("LockedSet").
  
  
  
  • The locked set only contains one record: namely the first locked record encountered.
  
  
  
  


• Therefore, to test for success, you need to check OK and the locked set. For example:
  
  
  
  
  

  If ((OK=1) & (Records in set("LockedSet")=0)) ` The SET QUERY AND LOCK succeeded.