Remote SQL Query

[Neels]

Hi all

Is it possible for the Unistream series to respond to an external SQL Query. I have a client that has a  database  that wants to request data from the PLC instead of the PLC pushing data to the database?

[Simon]

Hi Neels,

UniStream is only an SQL client.  I'm not aware of situations where an SQL client can respond to requests.  I have done some quick google searches and there are situaitons where two SQL systems are set up as master and slave where they can request data from each other, but in those cases both master and slave are both SQL servers, and the purpose is to keep backup copies of data.

Just another thought, if the customer installed MQTT broker and client software on their SQL server, they should (?) be able to set up the MQTT client as a subscriber to the MQTT data, and it would push new data to the SQL databse.  The PLC would only publish data as it was relevant, which would optimise the data flow to the main SQL database.  There should be controllability on the update rate at both the subscriber end as well as the publisher end. 

Going back to the idea of the UniStream connecting directly to the main SQL databse, It is possible to set the PLC to only push data to the SQL server on change of state.  Maybe the server could send an SNMP packet to the UniStream that would trigger an SQL push?

As I said, just some thoughts, based on general principles and completely un-tested...

Simon