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However , if you tend to access some data more than others , and there is an index that groups them together , you will benefit from using CLUSTER . In the latter case , the messages may vary between platforms , but should reflect similar information . There must be ' <' and '> ' ordering operators having the same left and right input datatypes as the mergejoinable operator itself . These operators must be named ' <' and '> ' ; you do not have any choice in the matter , since there is no provision for specifying them explicitly . Every entry in the targetlist contains an expression that can be a constant value , a variable pointing to an attribute of one of the relations in the rangetable , a parameter or an expression tree made of function calls , constants , variables , operators etc. the qualification The queries qualification is an expression much like one of those contained in the targetlist entries . As an engineer at Exponent , she investigates geotechnical and environmental projects . The Slinkys race downward all by themselves . Her engineering analyses have supported accelerating the timing of when the fuel can be loaded into the reactor vessel , increasing the overall efficiency of the reactor construction process and potentially saving the Program millions of dollars . The CREATE VIEW command for the shoelace view ( which is the simplest one we have ) will create a relation shoelace and an entry in pg_rewrite that tells that there is a rewrite rule that must be applied whenever the relation shoelace is referenced in a queries rangetable . However , if you want to make the retrieval efficient , you 'll have to resort to the means your RDBMS provider gives you - be it an index , my imaginary MEMSTORE command , or an intelligent RDBMS which creates indices without your knowledge based on the fact that you have sent it many queries based on a specific combination of keys ... Le is an active member of the American Society of Mechanical Engineers , and recently joined the Project Management Institute and the International Council on Systems Engineering . When they are the same , the notify event is one 's own work bouncing back , and can be ignored .