Joins

• Order sometimes does matter (join_collapse_limit)
   
• If RIGHT and LEFT joins have "null-exempt" qualifiers, consider making a regular join

  SELECT c.relname,n.nspname FROM pg_class c
  LEFT JOIN pg_namespace n ON (c.relnamespace = n.oid);
  
  
  SELECT c.relname,n.nspname FROM pg_class c
  LEFT JOIN pg_namespace n ON (c.relnamespace = n.oid);
  WHERE n.nspname = 'public'
  

  
   
• Hash Join is usually the best operator, followed closely by Merge Join. Nested Loop is not preferred. (format of each)
   
• RIGHT vs. LEFT

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