Does the order of columns of varying size have any effect on SELECT/INSERT/UPDATE/and/or/DELETE performance? Take the example where an integer primary key is listed first in the table and alternatively listed after some large varchar or text columns? For example, is this different performance-wise:

   foo_id serial,
   foo_data varchar(8000),
   primary key (foo_id)

from this?

   bar_data varchar(8000),
   bar_id serial,
   primary key (bar_id)

My suspicion is it would never make a difference since the index will be searched when querying "WHERE [foo|bar]_id=?" (as long as the planner decides to use the index).

What about a case where a sequential scan _must_ be performed? Could the order of columns make a difference in the number of pages read/written if there is a mix of small and large columns?

Thanks for your help.

Best Regards,

Bill Montgomery

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