[postgis-users] Loop or Cursor

[Bob Pawley]

Hi Leo

I'm developing a geometric system as opposed to geographic (basically an engineering drawing).

I have a fixed field, representing a peice of paper, within which the user can add one to four objects.

These object are placed within the field according to the total number of objects.

The first object 'A' is placed in the center and then the user adds lines (one to eight at the moment) as attributes to the object.

When the user adds a second object, I want to update the attributes of object A to satisfy the new placement of object A.

When the user places a third object then both, object A and B, need to be updated.

At the moment, my updates haven't worked as I get  either a null or multiple return.

Any suggestions for updating the lines for each object would be greatly appreciated.

Thanks

Bob


  ----- Original Message ----- 
  From: Paragon Corporation 
  To: 'PostGIS Users Discussion' 
  Sent: Monday, July 20, 2009 7:45 PM
  Subject: Re: [postgis-users] Loop or Cursor


  What kind of operation?  Even an update statement might suffice.  There are many ways to cleverly control the flow of an update that do not necessitate doing a loop or cursor.

  Also keep in mind even within a function used in a  SELECT statement of a query, PostgreSQL allows you to run updates and do all sorts of crazy things like launch perl scripts and bash scripts.  So for example you can mail to your whole membership simple by doing this

  SELECT member_name, send_mail(member_id) As did_it_send
  FROM membership
  WHERE gross_income > 1000000 and active = true


  It is very convenient for making rule processors.

  Leo




------------------------------------------------------------------------------
  From: postgis-users-bounces at postgis.refractions.net [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Bob Pawley
  Sent: Monday, July 20, 2009 1:43 PM
  To: PostGIS Users Discussion
  Subject: [postgis-users] Loop or Cursor


  Hi

  I need to access a number of rows, one at a time to perform an operation on each.

  Under what conditions would I consider using a loop command, rather than (or with) a cursor?

  Bob


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