PostgreSQL 10 High Performance - Third Edition

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 ...