dbi::faq.3

视频监控网络部分的协议ddns,的模块的实现代码,请大家大胆指正.

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\&    http://www.hughes.com.au
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.PP
You may also wish to look at MySQL which is a more powerful database engine
that has a similar feel to mSQL.
.PP
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\&    http://www.tcx.se
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.PP
If the dataset is larger than 1 million row tables or 1000 tables, or if you
have either more money, or larger machines, I would recommend \fIOracle \s-1RDBMS\s0\fR.
Oracle's \s-1WWW\s0 site is an excellent source of more information.
.PP
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\&    http://www.oracle.com
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.PP
\&\fIInformix\fR is another high-end \s-1RDBMS\s0 that is worth considering. There are
several differences between Oracle and Informix which are too complex for
this document to detail. Information on Informix can be found on their
\&\s-1WWW\s0 site at:
.PP
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\&    http://www.informix.com
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.PP
In the case of \s-1WWW\s0 fronted applications, \fImSQL\fR may be a better option
due to slow connection times between a \s-1CGI\s0 script and the Oracle \s-1RDBMS\s0 and
also the amount of resource each Oracle connection will consume. \fImSQL\fR
is lighter resource-wise and faster.
.PP
These views are not necessarily representative of anyone else's opinions,
and do not reflect any corporate sponsorship or views. They are provided
\&\fIas-is\fR.
.Sh "3.8 Is <\fIinsert feature here\fP> supported in \s-1DBI\s0?"
.IX Subsection "3.8 Is <insert feature here> supported in DBI?"
Given that we're making the assumption that the feature you have requested
is a non-standard database-specific feature, then the answer will be \fIno\fR.
.PP
\&\s-1DBI\s0 reflects a \fIgeneric\fR \s-1API\s0 that will work for most databases, and has
no database-specific functionality.
.PP
However, driver authors may, if they so desire, include hooks to database-specific
functionality through the \f(CW\*(C`func()\*(C'\fR method defined in the \s-1DBI\s0 \s-1API\s0.
Script developers should note that use of functionality provided \fIvia\fR
the \f(CW\*(C`func()\*(C'\fR methods is very unlikely to be portable across databases.
.SH "Programming Questions"
.IX Header "Programming Questions"
.Sh "4.1 Is \s-1DBI\s0 any use for \s-1CGI\s0 programming?"
.IX Subsection "4.1 Is DBI any use for CGI programming?"
In a word, yes! \s-1DBI\s0 is hugely useful for \s-1CGI\s0 programming! In fact, I would
tentatively say that \s-1CGI\s0 programming is one of two top uses for \s-1DBI\s0.
.PP
\&\s-1DBI\s0 confers the ability to \s-1CGI\s0 programmers to power WWW-fronted databases
to their users, which provides users with vast quantities of ordered
data to play with. \s-1DBI\s0 also provides the possibility that, if a site is
receiving far too much traffic than their database server can cope with, they
can upgrade the database server behind the scenes with no alterations to
the \s-1CGI\s0 scripts.
.Sh "4.2 How do I get faster connection times with DBD::Oracle and \s-1CGI\s0?"
.IX Subsection "4.2 How do I get faster connection times with DBD::Oracle and CGI?"
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\&    Contributed by John D. Groenveld
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.PP
The Apache \f(CW\*(C`httpd\*(C'\fR maintains a pool of \f(CW\*(C`httpd\*(C'\fR children to service client 
requests.
.PP
Using the Apache \fImod_perl\fR module by \fIDoug MacEachern\fR, the perl 
interpreter is embedded with the \f(CW\*(C`httpd\*(C'\fR children. The \s-1CGI\s0, \s-1DBI\s0, and your 
other favorite modules can be loaded at the startup of each child. These 
modules will not be reloaded unless changed on disk.
.PP
For more information on Apache, see the Apache Project's \s-1WWW\s0 site:
.PP
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\&    http://www.apache.org
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.PP
The \fImod_perl\fR module can be downloaded from \s-1CPAN\s0 \fIvia\fR:
.PP
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\&    http://www.perl.com/cgi\-bin/cpan_mod?module=Apache
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.Sh "4.3 How do I get persistent connections with \s-1DBI\s0 and \s-1CGI\s0?"
.IX Subsection "4.3 How do I get persistent connections with DBI and CGI?"
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\&    Contributed by John D. Groenveld
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.PP
Using Edmund Mergl's \fIApache::DBI\fR module, database logins are stored in a 
hash with each of these \f(CW\*(C`httpd\*(C'\fR child. If your application is based on a 
single database user, this connection can be started with each child. 
Currently, database connections cannot be shared between \f(CW\*(C`httpd\*(C'\fR children.
.PP
\&\fIApache::DBI\fR can be downloaded from \s-1CPAN\s0 \fIvia\fR:
.PP
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\&    http://www.perl.com/cgi\-bin/cpan_mod?module=Apache::DBI
.Ve
.ie n .Sh "4.4 ``When I run a perl script from the command line, it works, but, when I run it under the ""httpd"", it fails!'' Why?"
.el .Sh "4.4 ``When I run a perl script from the command line, it works, but, when I run it under the \f(CWhttpd\fP, it fails!'' Why?"
.IX Subsection "4.4 ``When I run a perl script from the command line, it works, but, when I run it under the httpd, it fails!'' Why?"
Basically, a good chance this is occurring is due to the fact that the user
that you ran it from the command line as has a correctly configured set of
environment variables, in the case of \fIDBD::Oracle\fR, variables like
\&\f(CW\*(C`ORACLE_HOME\*(C'\fR, \f(CW\*(C`ORACLE_SID\*(C'\fR or \f(CW\*(C`TWO_TASK\*(C'\fR.
.PP
The \f(CW\*(C`httpd\*(C'\fR process usually runs under the user id of \f(CW\*(C`nobody\*(C'\fR,
which implies there is no configured environment. Any scripts attempting to
execute in this situation will correctly fail.
.PP
One way to solve this problem is to set the environment for your database in a
\&\f(CW\*(C`BEGIN { }\*(C'\fR block at the top of your script. Another technique is to configure
your \s-1WWW\s0 server to pass-through certain environment variables to your \s-1CGI\s0 
scripts.
.PP
Similarly, you should check your \f(CW\*(C`httpd\*(C'\fR error logfile for any clues,
as well as the ``Idiot's Guide To Solving Perl / \s-1CGI\s0 Problems'' and
``Perl \s-1CGI\s0 Programming \s-1FAQ\s0'' for further information. It is
unlikely the problem is DBI-related.
.PP
The ``Idiot's Guide To Solving Perl / \s-1CGI\s0 Problems'' can be located at:
.PP
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\&    http://www.perl.com/perl/faq/index.html
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.PP
as can the ``Perl \s-1CGI\s0 Programming \s-1FAQ\s0''. Read \fI\s-1BOTH\s0\fR these documents 
carefully!
.ie n .Sh "4.5 How do I get the number of rows returned from a ""SELECT"" statement?"
.el .Sh "4.5 How do I get the number of rows returned from a \f(CWSELECT\fP statement?"
.IX Subsection "4.5 How do I get the number of rows returned from a SELECT statement?"
Count them. Read the \s-1DBI\s0 docs for the \f(CW\*(C`rows()\*(C'\fR method.
.SH "Miscellaneous Questions"
.IX Header "Miscellaneous Questions"
.Sh "5.1 Can I do multi-threading with \s-1DBI\s0?"
.IX Subsection "5.1 Can I do multi-threading with DBI?"
Perl version 5.005 and later can be built to support multi-threading.
The \s-1DBI\s0, as of version 1.02, does not yet support multi-threading
so it would be unsafe to let more than one thread enter the \s-1DBI\s0 at
the same time.
.PP
It is expected that some future version of the \s-1DBI\s0 will at least be
thread-safe (but not thread-hot) by automatically blocking threads
intering the \s-1DBI\s0 while it's already in use.
.PP
For some \s-1OCI\s0 example code for Oracle that has multi-threaded \f(CW\*(C`SELECT\*(C'\fR
statements, see:
.PP
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\&    http://www.symbolstone.org/technology/oracle/oci/orathreads.tar.gz
.Ve
.Sh "5.2 How do I handle \s-1BLOB\s0 data with \s-1DBI\s0?"
.IX Subsection "5.2 How do I handle BLOB data with DBI?"
Handling \s-1BLOB\s0 data with the \s-1DBI\s0 is very straight-forward. \s-1BLOB\s0 columns are
specified in a \s-1SELECT\s0 statement as per normal columns. However, you also
need to specify a maximum \s-1BLOB\s0 size that the <I>database handle</I> can
fetch using the \f(CW\*(C`LongReadLen\*(C'\fR attribute.
.PP
For example:
.PP
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\&    ### $dbh is a connected database handle
\&    $sth = $dbh\->prepare( "SELECT blob_column FROM blobby_table" );
\&    $sth\->execute;
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.PP
would fail.
.PP
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\&    ### $dbh is a connected database handle
\&    ### Set the maximum BLOB size...
\&    $dbh\->{LongReadLen} = 16384;        ### 16Kb...Not much of a BLOB!
\&
\&    $sth = $dbh\->prepare( "..." );
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.PP
would succeed <I>provided no column values were larger than the specified
value</I>.
.PP
If the \s-1BLOB\s0 data is longer than the value of \f(CW\*(C`LongReadLen\*(C'\fR, then an
error will occur. However, the \s-1DBI\s0 provides an additional piece of
functionality that will automatically truncate the fetched \s-1BLOB\s0 to the
size of \f(CW\*(C`LongReadLen\*(C'\fR if it is longer. This does not cause an error to
occur, but may make your fetched \s-1BLOB\s0 data useless.
.PP
This behaviour is regulated by the \f(CW\*(C`LongTruncOk\*(C'\fR attribute which is 
defaultly set to a false value ( thus making overlong \s-1BLOB\s0 fetches fail ).
.PP
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\&    ### Set BLOB handling such that it\*(Aqs 16Kb and can be truncated
\&    $dbh\->{LongReadLen} = 16384;
\&    $dbh\->{LongTruncOk} = 1;
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.PP
Truncation of \s-1BLOB\s0 data may not be a big deal in cases where the \s-1BLOB\s0
contains run-length encoded data, but data containing checksums at the end,
for example, a \s-1ZIP\s0 file, would be rendered useless.
.Sh "5.3 How can I invoke stored procedures with \s-1DBI\s0?"
.IX Subsection "5.3 How can I invoke stored procedures with DBI?"
The \s-1DBI\s0 does not define a database-independent way of calling stored procedures.
.PP
However, most database that support them also provide a way to call
them from \s-1SQL\s0 statements \- and the \s-1DBI\s0 certainly supports that.
.PP
So, assuming that you have created a stored procedure within the target
database, \fIeg\fR, an Oracle database, you can use \f(CW$dbh\fR\->\f(CW\*(C`do()\*(C'\fR to
immediately execute the procedure. For example,
.PP
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\&    $dbh\->do( "BEGIN someProcedure; END;" );   # Oracle\-specific
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.PP
You should also be able to \f(CW\*(C`prepare\*(C'\fR and \f(CW\*(C`execute\*(C'\fR, which is
the recommended way if you'll be calling the procedure often.
.Sh "5.4 How can I get return values from stored procedures with \s-1DBI\s0?"
.IX Subsection "5.4 How can I get return values from stored procedures with DBI?"
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\&    Contributed by Jeff Urlwin
\&
\&    $sth = $dbh\->prepare( "BEGIN foo(:1, :2, :3); END;" );
\&    $sth\->bind_param(1, $a);
\&    $sth\->bind_param_inout(2, \e$path, 2000);
\&    $sth\->bind_param_inout(3, \e$success, 2000);
\&    $sth\->execute;
.Ve
.PP
Remember to perform error checking, though! ( Or use the \f(CW\*(C`RaiseError\*(C'\fR
attribute ).
.Sh "5.5 How can I create or drop a database with \s-1DBI\s0?"
.IX Subsection "5.5 How can I create or drop a database with DBI?"
Database creation and deletion are concepts that are entirely too abstract
to be adequately supported by \s-1DBI\s0. For example, Oracle does not support the
concept of dropping a database at all! Also, in Oracle, the database
\&\fIserver\fR essentially \fIis\fR the database, whereas in mSQL, the
server process runs happily without any databases created in it. The
problem is too disparate to attack in a worthwhile way.
.PP
Some drivers, therefore, support database creation and deletion through
the private \f(CW\*(C`func()\*(C'\fR methods. You should check the documentation for
the drivers you are using to see if they support this mechanism.
.ie n .Sh "5.6 How can I ""commit""\fP or \f(CW""rollback"" a statement with \s-1DBI\s0?"
.el .Sh "5.6 How can I \f(CWcommit\fP or \f(CWrollback\fP a statement with \s-1DBI\s0?"
.IX Subsection "5.6 How can I commit or rollback a statement with DBI?"
See the \f(CW\*(C`commit()\*(C'\fR and \f(CW\*(C`rollback()\*(C'\fR methods in the \s-1DBI\s0 Specification.
.PP
Chapter 6 of \*(L"Programming the Perl \s-1DBI\s0\*(R" discusses transaction handling within
the context of \s-1DBI\s0 in more detail.
.ie n .Sh "5.7 How are ""NULL"" values handled by \s-1DBI\s0?"
.el .Sh "5.7 How are \f(CWNULL\fP values handled by \s-1DBI\s0?"
.IX Subsection "5.7 How are NULL values handled by DBI?"
\&\f(CW\*(C`NULL\*(C'\fR values in \s-1DBI\s0 are specified to be treated as the value \f(CW\*(C`undef\*(C'\fR.
\&\f(CW\*(C`NULL\*(C'\fRs can be inserted into databases as \f(CW\*(C`NULL\*(C'\fR, for example:
.PP
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\&    $rv = $dbh\->do( "INSERT INTO table VALUES( NULL )" );
.Ve
.PP
but when queried back, the \f(CW\*(C`NULL\*(C'\fRs should be tested against \f(CW\*(C`undef\*(C'\fR.
This is standard across all drivers.
.ie n .Sh "5.8 What are these ""func()"" methods all about?"
.el .Sh "5.8 What are these \f(CWfunc()\fP methods all about?"
.IX Subsection "5.8 What are these func() methods all about?"
The \f(CW\*(C`func()\*(C'\fR method is defined within \s-1DBI\s0 as being an entry point
for database-specific functionality, \fIeg\fR, the ability to create or
drop databases. Invoking these driver-specific methods is simple, for example,
to invoke a \f(CW\*(C`createDatabase\*(C'\fR method that has one argument, we would
write:
.PP
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\&    $rv =$dbh\->func( \*(Aqargument\*(Aq, \*(AqcreateDatabase\*(Aq );
.Ve
.PP
Software developers should note that the \f(CW\*(C`func()\*(C'\fR methods are
non-portable between databases.
.Sh "5.9 Is \s-1DBI\s0 Year 2000 Compliant?"
.IX Subsection "5.9 Is DBI Year 2000 Compliant?"
\&\s-1DBI\s0 has no knowledge of understanding of what dates are. Therefore, \s-1DBI\s0
itself does not have a Year 2000 problem. Individual drivers may use date
handling code internally and therefore be potentially susceptible to the
Year 2000 problem, but this is unlikely.
.PP
You may also wish to read the ``Does Perl have a Year 2000 problem?'' section
of the Perl \s-1FAQ\s0 at:
.PP
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\&    http://www.perl.com/CPAN/doc/FAQs/FAQ/PerlFAQ.html
.Ve
.SH "Support and Training"
.IX Header "Support and Training"
The Perl5 Database Interface is \fI\s-1FREE\s0\fR software. \s-1IT\s0 \s-1COMES\s0 \s-1WITHOUT\s0 \s-1WARRANTY\s0
\&\s-1OF\s0 \s-1ANY\s0 \s-1KIND\s0. See the \s-1DBI\s0 \s-1README\s0 for more details.
.PP
However, some organizations are providing either technical support or
training programs on \s-1DBI\s0. The present author has no knowledge as
to the quality of these services. The links are included for reference
purposes only and should not be regarded as recommendations in any way.
\&\fICaveat emptor\fR.
.Sh "Commercial Support"
.IX Subsection "Commercial Support"
.IP "The Perl Clinic" 4
.IX Item "The Perl Clinic"
The Perl Clinic provides commercial support for \fIPerl\fR and Perl
related problems, including the \fI\s-1DBI\s0\fR and its drivers.  Support is
provided by the company with whom Tim Bunce, author of \fI\s-1DBI\s0\fR and
\&\fIDBD::Oracle\fR, works and ActiveState. For more information on their
services, please see:
.Sp
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\&    http://www.perlclinic.com
.Ve
.Sh "Training"
.IX Subsection "Training"
.IP "Westlake Solutions" 4
.IX Item "Westlake Solutions"
A hands-on class for experienced Perl \s-1CGI\s0 developers that teaches
how to write database-connected \s-1CGI\s0 scripts using Perl and \s-1DBI\s0.pm.  This
course, along with four other courses on \s-1CGI\s0 scripting with Perl, is
taught in Washington, \s-1DC\s0; Arlington, Virginia; and on-site worldwide upon
request.
.Sp
See:
.Sp
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\&    http://www.westlake.com/training
.Ve
.Sp
for more details.
.SH "Other References"
.IX Header "Other References"
In this section, we present some miscellaneous \s-1WWW\s0 links that may be of
some interest to \s-1DBI\s0 users. These are not verified and may result in
unknown sites or missing documents.
.PP
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\&    http://www\-ccs.cs.umass.edu/db.html
\&    http://www.odmg.org/odmg93/updates_dbarry.html
\&    http://www.jcc.com/sql_stnd.html
.Ve
.SH "AUTHOR"
.IX Header "AUTHOR"
Alligator Descartes <\fIhttp://www.symbolstone.org/descarte/contact.html\fR>. 
Portions are Copyright their original stated authors.
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
This document is Copyright (c)1994\-2000 Alligator Descartes, with portions
Copyright (c)1994\-2000 their original authors. This module is released under
the 'Artistic' license which you can find in the perl distribution.
.PP
This document is Copyright (c)1997\-2000 Alligator Descartes. All rights reserved.
Permission to distribute this document, in full or in part, via email,
Usenet, ftp archives or http is granted providing that no charges are involved,
reasonable attempt is made to use the most current version and all credits
and copyright notices are retained ( the \fI\s-1AUTHOR\s0\fR and \fI\s-1COPYRIGHT\s0\fR sections ).
Requests for other distribution rights, including incorporation into 
commercial products, such as books, magazine articles or CD-ROMs should be
made to Alligator Descartes <\fIhttp://www.symbolstone.org/descarte/contact.html\fR>.