commit 97be1d06e5f61f9b679a14dc5b6ec189cdde42ff
Author: Wolfgang Hottgenroth <w.hottgenroth@krohne.com>
Date:   Fri May 21 13:24:44 2021 +0200

    total function

diff --git a/function_total_energy_by_day_and_device.sql b/function_total_energy_by_day_and_device.sql
new file mode 100644
index 0000000..956a68e
--- /dev/null
+++ b/function_total_energy_by_day_and_device.sql
@@ -0,0 +1,37 @@
+create or replace function total_energy_by_day_and_device(p_day date, p_device varchar)
+  returns double precision
+  language plpgsql
+  as $$
+  declare
+    v_firstEnergy double precision;
+    v_lastEnergy double precision;
+    v_total double precision;
+  begin
+    select energy
+      into v_lastEnergy
+      from power_measurement_t
+        where time = (
+                       select max(time)
+                         from power_measurement_t
+                         where time between p_day + time '00:00' and p_day + time '00:00' + interval '24h' and
+                               deviceid = p_device and
+                               status = 'Ok'
+                     ) and
+              deviceid = p_device;
+    select energy
+      into v_firstEnergy
+      from power_measurement_t
+        where time = (
+                       select min(time)
+                         from power_measurement_t
+                         where time between p_day + time '00:00' and p_day + time '00:00' + interval '24h' and 
+                               deviceid = p_device and 
+                               status = 'Ok'
+                     ) and
+              deviceid = p_device;
+    v_total := v_lastEnergy - v_firstEnergy;
+    return v_total;
+  end;
+$$;
+
+