add sequence part

IT/SQL/PostgreSQL/Upgrade.md

@@ -26,3 +26,20 @@ pg_upgrade -b /opt/pgsql-PG_VERSION/bin -B /usr/bin -d /var/lib/postgres/olddata
 ```
 - check both pg_hba.conf in new  and old cluster
 - restart server `sc-start postgresql`
+
+# sequece manipulation
+
+sequence are use to generate uniq identifier
+- get sequence value
+```SQL
+select * from name_seq;
+```
+- increment sequence value
+```SQL
+select nextval(name_seq);
+```
+
+- set sequence value:
+```SQL
+select setval(name_seq,newvalue);
+```