1DBD::SQLite2(3) User Contributed Perl Documentation DBD::SQLite2(3)
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6 DBD::SQLite2 - Self Contained RDBMS in a DBI Driver (sqlite 2.x)
7
9 use DBI;
10 my $dbh = DBI->connect("dbi:SQLite2:dbname=dbfile","","");
11
13 SQLite is a public domain RDBMS database engine that you can find at
14 http://www.sqlite.org/.
15 Rather than ask you to install SQLite first, because SQLite is public
17 domain, DBD::SQLite2 includes the entire thing in the distribution. So
18 in order to get a fast transaction capable RDBMS working for your perl
19 project you simply have to install this module, and nothing else.
20 For real work please use the updated DBD::SQLite driver with the up-to-
22 date sqlite3 backend. SQLite2 supports the following features:
23 Implements a large subset of SQL92
25 See http://www.sqlite.org/lang.html for details.
26 A complete DB in a single disk file
28 Everything for your database is stored in a single disk file,
29 making it easier to move things around than with DBD::CSV.
30 Atomic commit and rollback
32 Yes, DBD::SQLite2 is small and light, but it supports full
33 transactions
34 Extensible
36 User-defined aggregate or regular functions can be registered with
37 the SQL parser.
38 There's lots more to it, so please refer to the docs on the SQLite web
40 page, listed above, for SQL details. Also refer to DBI for details on
41 how to use DBI itself.
42
44 The API works like every DBI module does. Please see DBI for more
45 details about core features.
46 Currently many statement attributes are not implemented or are limited
48 by the typeless nature of the SQLite2 database.
49
51 Database Handle Attributes
52 sqlite_version
53 Returns the version of the SQLite library which DBD::SQLite2 is
54 using, i.e, "2.8.15".
55 sqlite_encoding
57 Returns either "UTF-8" or "iso8859" to indicate how the SQLite
58 library was compiled.
59 sqlite_handle_binary_nulls
61 Set this attribute to 1 to transparently handle binary nulls in
62 quoted and returned data.
63 NOTE: This will cause all backslash characters ("\") to be doubled
65 up in all columns regardless of whether or not they contain binary
66 data or not. This may break your database if you use it from
67 another application. This does not use the built in
68 "sqlite_encode_binary" and "sqlite_decode_binary" functions, which
69 may be considered a bug.
70
72 $dbh->func('last_insert_rowid')
73 This method returns the last inserted rowid. If you specify an INTEGER
74 PRIMARY KEY as the first column in your table, that is the column that
75 is returned. Otherwise, it is the hidden ROWID column. See the sqlite
76 docs for details.
77 $dbh->func( $name, $argc, $func_ref, "create_function" )
79 This method will register a new function which will be useable in SQL
80 query. The method's parameters are:
81 $name
83 The name of the function. This is the name of the function as it
84 will be used from SQL.
85 $argc
87 The number of arguments taken by the function. If this number is
88 -1, the function can take any number of arguments.
89 $func_ref
91 This should be a reference to the function's implementation.
92 For example, here is how to define a now() function which returns the
94 current number of seconds since the epoch:
95 $dbh->func( 'now', 0, sub { return time }, 'create_function' );
97 After this, it could be use from SQL as:
99 INSERT INTO mytable ( now() );
101 $dbh->func( $name, $argc, $pkg, 'create_aggregate' )
103 This method will register a new aggregate function which can then used
104 from SQL. The method's parameters are:
105 $name
107 The name of the aggregate function, this is the name under which
108 the function will be available from SQL.
109 $argc
111 This is an integer which tells the SQL parser how many arguments
112 the function takes. If that number is -1, the function can take any
113 number of arguments.
114 $pkg
116 This is the package which implements the aggregator interface.
117 The aggregator interface consists of defining three methods:
119 new()
121 This method will be called once to create an object which should be
122 used to aggregate the rows in a particular group. The step() and
123 finalize() methods will be called upon the reference return by the
124 method.
125 step(@_)
127 This method will be called once for each rows in the aggregate.
128 finalize()
130 This method will be called once all rows in the aggregate were
131 processed and it should return the aggregate function's result.
132 When there is no rows in the aggregate, finalize() will be called
133 right after new().
134 Here is a simple aggregate function which returns the variance (example
136 adapted from pysqlite):
137 package variance;
139 sub new { bless [], shift; }
141 sub step {
143 my ( $self, $value ) = @_;
144 push @$self, $value;
146 }
147 sub finalize {
149 my $self = $_[0];
150 my $n = @$self;
152 # Variance is NULL unless there is more than one row
154 return undef unless $n || $n == 1;
155 my $mu = 0;
157 foreach my $v ( @$self ) {
158 $mu += $v;
159 }
160 $mu /= $n;
161 my $sigma = 0;
163 foreach my $v ( @$self ) {
164 $sigma += ($x - $mu)**2;
165 }
166 $sigma = $sigma / ($n - 1);
167 return $sigma;
169 }
170 $dbh->func( "variance", 1, 'variance', "create_aggregate" );
172 The aggregate function can then be used as:
174 SELECT group_name, variance(score) FROM results
176 GROUP BY group_name;
177
179 To access the database from the command line, try using dbish which
180 comes with the DBI module. Just type:
181 dbish dbi:SQLite:foo.db
183 On the command line to access the file foo.db.
185 Alternatively you can install SQLite from the link above without
187 conflicting with DBD::SQLite2 and use the supplied "sqlite" command
188 line tool.
189
191 SQLite is fast, very fast. I recently processed my 72MB log file with
192 it, inserting the data (400,000+ rows) by using transactions and only
193 committing every 1000 rows (otherwise the insertion is quite slow), and
194 then performing queries on the data.
195 Queries like count(*) and avg(bytes) took fractions of a second to
197 return, but what surprised me most of all was:
198 SELECT url, count(*) as count FROM access_log
200 GROUP BY url
201 ORDER BY count desc
202 LIMIT 20
203 To discover the top 20 hit URLs on the site (http://axkit.org), and it
205 returned within 2 seconds. I'm seriously considering switching my log
206 analysis code to use this little speed demon!
207 Oh yeah, and that was with no indexes on the table, on a 400MHz PIII.
209 For best performance be sure to tune your hdparm settings if you are
211 using linux. Also you might want to set:
212 PRAGMA default_synchronous = OFF
214 Which will prevent sqlite from doing fsync's when writing (which slows
216 down non-transactional writes significantly) at the expense of some
217 peace of mind. Also try playing with the cache_size pragma.
218
220 Likely to be many, please use http://rt.cpan.org/ for reporting bugs.
221
223 Matt Sergeant, matt@sergeant.org
224 Perl extension functions contributed by Francis J. Lacoste
226 <flacoste@logreport.org> and Wolfgang Sourdeau
227 <wolfgang@logreport.org>. Maintenance help by Reini Urban
228 <rurban@cpan.org>
229
231 This module is available under the same licences as perl, the Artistic
232 license and the GPL.
233
235 DBD::SQLite, DBI.
236perl v5.34.0 2021-07-22 DBD::SQLite2(3)