Question

I’m writing a stored procedure that should sync a table from our production environment to our test environment (once a day).
I have 2 tables. To make it easy lets call them Meters and Measurements.

Meters = [Meter_id, Location]
Measurements = [Meter_id, Value, MeasurementTime]

I want to keep Measurements in sync and lets assume that I can manually add a meter to my test environment. Meter_id can get out of sync between both databases but Location doesn’t change.

I have set up a database link to our test server called db_test. Now I would like to use a Merge statement to update Measurements@db_test

MERGE INTO Measurements@db_test meas_test
USING Measurements meas
   ON (???)
WHEN MATCHED THEN
   -- Do update
WHEN NOT MATCHED THEN
   -- Do insert

I was thinking in this direction…

MERGE INTO Measurements@db_test meas_test
USING (SELECT value, location 
       FROM meters mtr, measurements meas 
       WHERE mtr.meter_id = meas.meter_id AND 
       MeasurementTime > sysdate - 1)  meas_new
ON ( meas_new.location = ??? AND 
     meas_new.value = meas_test.value AND 
     meas_new.MeasurementTime = meas_test.MeasurementTime)            
WHEN MATCHED THEN
   -- Do update
WHEN NOT MATCHED THEN
   -- Do insert

So how do I lay the join to the Meters table so that I’m sure they match on location and not on ID

Answer 1

Can’t you just join to the test environment’s Meters table over the link? Like this:

MERGE INTO measurements@db_test meas_test
USING (SELECT mtr_test.meter_id, meas.value, meas.measurementtime
         FROM meters mtr, measurements meas, meters@db_test mtr_test
        WHERE mtr.meter_id = meas.meter_id
          AND mtr_test.location = mtr.location
          AND meas.measurementtime > sysdate - 1) meas_new
   ON (meas_new.meter_id = meas_test.meter_id
       AND meas_new.value = meas_test.value
       AND meas_new.measurementtime = meas_test.measurementtime)
 WHEN MATCHED THEN
      -- Do update
 WHEN NOT MATCHED THEN
      -- Do insert