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Full Discussion: perl: help with DBI
Top Forums Shell Programming and Scripting perl: help with DBI Post 302424535 by SFNYC on Tuesday 25th of May 2010 02:09:04 PM
Old 05-25-2010
What database are you using? There may be a way to code the SQL to return you some count or indicator when no rows are returned from your SELECT.

There is also a method called 'rows', but it does not work for SELECT statements.

From perldoc DBI:

Code:
$rv = $sth->rows;

Returns the number of rows affected by the last row-affecting command, or -1 if the number of rows is not known or not available.

Generally, you can only rely on a row count after a non-SELECT execute (for some specific operations like UPDATE and DELETE), or after fetching all the rows of a SELECT statement.

For SELECT statements, it is generally not possible to know how many rows will be returned except by fetching them all. Some drivers will return the number of rows the application has fetched so far, but others may return -1 until all rows have been fetched. So use of the rows method or $DBI::rows with SELECT statements is not recommended.

One alternative method to get a row count for a SELECT is to execute a "SELECT COUNT(*) FROM ..." SQL statement with the same "..." as your query, and then fetch the row count from that.

 

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LEARN ABOUT MINIX

ppmtosixel

ppmtosixel(1)                                                 General Commands Manual                                                ppmtosixel(1)

NAME

       ppmtosixel - convert a portable pixmap into DEC sixel format

SYNOPSIS

       ppmtosixel [-raw] [-margin] [ppmfile]

DESCRIPTION

       Reads  a  portable  pixmap  as input.  Produces sixel commands (SIX) as output.  The output is formatted for color printing, e.g. for a DEC
       LJ250 color inkjet printer.

       If RGB values from the PPM file do not have maxval=100, the RGB values are rescaled.  A printer control header and a color assignment table
       begin the SIX file.  Image data is written in a compressed format by default.  A printer control footer ends the image file.

OPTIONS

       -raw   If  specified,  each  pixel  will  be explicitly described in the image file.  If -raw is not specified, output will default to com-
              pressed format in which identical adjacent pixels are replaced by "repeat pixel" commands.  A raw file is often an order  of  magni-
              tude larger than a compressed file and prints much slower.

       -margin
              If  -margin  is not specified, the image will be start at the left margin (of the window, paper, or whatever).  If -margin is speci-
              fied, a 1.5 inch left margin will offset the image.

PRINTING

       Generally, sixel files must reach the printer unfiltered.  Use the lpr -x option or cat filename > /dev/tty0?.

BUGS

       Upon rescaling, truncation of the least significant bits of RGB values may result in poor color conversion.  If the original PPM maxval was
       greater  than  100,  rescaling  also reduces the image depth.  While the actual RGB values from the ppm file are more or less retained, the
       color palette of the LJ250 may not match the colors on your screen.  This seems to be a printer limitation.

SEE ALSO

       ppm(5)

AUTHOR

       Copyright (C) 1991 by Rick Vinci.

                                                                   26 April 1991                                                     ppmtosixel(1)
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