--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/PostgreSQL/Plugins/GetLastChangeIndex.sql	Thu Jan 10 18:04:12 2019 +0100
@@ -0,0 +1,27 @@
+-- In PostgreSQL, the most straightforward query would be to run:
+
+--   SELECT currval(pg_get_serial_sequence('Changes', 'seq'))".
+
+-- Unfortunately, this raises the error message "currval of sequence
+-- "changes_seq_seq" is not yet defined in this session" if no change
+-- has been inserted before the SELECT. We thus track the sequence
+-- index with a trigger.
+-- http://www.neilconway.org/docs/sequences/
+
+INSERT INTO GlobalIntegers
+SELECT 6, CAST(COALESCE(MAX(seq), 0) AS BIGINT) FROM Changes;
+
+
+CREATE FUNCTION InsertedChangeFunc() 
+RETURNS TRIGGER AS $body$
+BEGIN
+  UPDATE GlobalIntegers SET value = new.seq WHERE key = 6;
+  RETURN NULL;
+END;
+$body$ LANGUAGE plpgsql;
+
+
+CREATE TRIGGER InsertedChange
+AFTER INSERT ON Changes
+FOR EACH ROW
+EXECUTE PROCEDURE InsertedChangeFunc();