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Programming the Perl DBI
book

Programming the Perl DBI

by Tim Bunce, Alligator Descartes
February 2000
Intermediate to advanced content levelIntermediate to advanced
364 pages
11h 47m
English
O'Reilly Media, Inc.
Content preview from Programming the Perl DBI

Slice array reference argument

It is also possible to use fetchall_arrayref( ) to return a data structure containing only certain columns from each row returned in the result set. For example, we might issue an SQL statement selecting the name, site_type, location, and mapref fields, but only wish to build an in-memory data structure for the rows name and location.

This cannot be done by the standard no-argument version of fetchall_arrayref( ), but is easily achieved by specifying an array slice as an argument to fetchall_arrayref( ).

Therefore, if our original SQL statement was:

SELECT meg.name, st.site_type, meg.location, meg.mapref
FROM megaliths meg, site_types st
WHERE meg.site_type_id = st.id

then the array indices for each returned row would map as follows:

name       -> 0
site_type  -> 1
location   -> 2
mapref     -> 3

By knowing these array indices for the columns, we can simply write:

### Retrieve the name and location fields...
$array_ref = $sth->fetchall_arrayref( [ 0, 2 ] );

The array indices are specified in the form standard to Perl itself, so you can quite easily use ranges and negative indices for special cases. For example:

### Retrieve the second last and last columns
$array_ref = $sth->fetchall_arrayref( [ -2, -1 ] );

### Fetch the first to third columns
$array_ref = $sth->fetchall_arrayref( [ 0 .. 2 ] );

The actual data structure created when fetchall_arrayref( ) is used like this is identical in form to the structure created by fetchall_arrayref( ) when invoked with no arguments. ...

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Publisher Resources

ISBN: 1565926994Supplemental ContentErrata Page