% @(#)createvirt.hlq	17.1.1.1 (ESO-IPG) 01/25/02 17:43:28
% @(#)createtabl.hlq	7.1 (ESO-IPG) 2/24/94 18:30:51 
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%.COPYRIGHT  (c)  1990 European Southern Observatory
%.IDENT      createvirt.hlq
%.AUTHOR     MP, IPG/ESO
%.KEYWORDS   MIDAS, help files, CREATE/VIRT
%.PURPOSE    On-line help file for the command: CREATE/VIRTUAL
%.VERSION    1.0  1-MAR-1994 : Creation, MP
%----------------------------------------------------------------
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SECTION./VIRT
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CREATE/VIRTUAL						1-MAR-1994   MP
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CREATE/VIRTUAL  virtual table
	create a virtual table from a physical table
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Purpose:      
             Create a virtual table from a physical table. 
             A virtual table doesn't contain any real data except
             for a selection column. Its other columns are assembled at
             run-time from the columns of the physical table.
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Syntax:       
             CREATE/VIRTUAL  virtual table
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             virtual    = name of the output virtual table 
\ap\pa
             table      = name of the physical table  
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Note:        
             No operation modifying the contents of a table is allowed on 
             a virtual table except for the SELECT/TABLE operation. 
             A virtual table may be projected or copied into a physical 
             table. 
             Virtual tables may be used, for instance  to access and manipulate
             local databases, i.e read-only tables without copying these tables
             into a private directory:

             CREATE/VIRTUAL esolv_virtual /midas/calib/data/esolv
               creates a virtual table esolv_virtual from the physical table 
               /midas/calib/data/esolv
             SELECT/TABLE esolv_virtual seq.le.1000
               selects the first 1000 entries of the virtual table esolv_virtual
             COPY/TABLE esolv_virtual myesolv
               copies the selected entries of esolv_virtual into a physical table
               myesolv

             The name of the physical table from which the virtual table is created is
             stored into the descriptor TVIEWTBL of the virtual table.

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See also:
             CREATE/TABLE
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Examples:
\ex
             CREATE/VIRTUAL esolv_virtual esolv 
             creates the virtual table esolv_virtual.tbl from the table esolv.tbl
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