PostgreSQL

Each table has a column CTID which holds the row id of a row.

SELECT ctid FROM mytable;

SELECT datname,usename,procpid,client_addr,waiting,query_start,current_query FROM pg_stat_activity;

The exception join can be created with the combination of the left outer join and the query on null.

Table a:

• id
• name

Table b:

• pid
• fid
• longitude
• latitude

Select every entry from table a which has no entry in table b.

  SELECT *
  FROM a LEFT OUTER JOIN b ON (a.id = b.fid)
  WHERE b.pid IS NULL

set enable_seqscan=true;
set enable_indexscan=true;

\d

\d table_name

\l