Description of the illustration lag.eps

LAG
  { ( value_expr [, offset [, default]]) [ { RESPECT | IGNORE } NULLS ] 
  | ( value_expr [ { RESPECT | IGNORE } NULLS ] [, offset [, default]] )
  }
  OVER 
 { window_name 
  | { [window_name] | [query_partition_clause] } order_by_clause 	      
}