Tuple id

Each row in the database has a tuple id, a number visible as the system column named ctid in each row. You can use these to look up a row:

SELECT ctid,customerid FROM customers limit 3;
 ctid  | customerid 
-------+------------
 (0,1) |          1
 (0,2) |          2
 (0,3) |          3

EXPLAIN SELECT customerid FROM customers WHERE ctid='(0,1)';
                       QUERY PLAN                        
---------------------------------------------------------
 Tid Scan on customers  (cost=0.00..4.01 rows=1 width=4)
   TID Cond: (ctid = '(0,1)'::tid)

These TID sequences cannot be relied upon as a stable way to access a particular row outside of a transaction, because common operations including UPDATE will change them. If you're referring to a row more than one in the same transaction, perhaps in a procedural programming language, the TID scan can be a quick way to operate a second time on a row located earlier. The ctid value can also be used to...