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<h2>Obtaining An License To Use SQLite</h2>

<p>
Even though SQLite is in the public domain and does not require
a license, some users want to obtain a license anyway.  Some reasons
for obtaining a license include:
</p>

<title>SQLite Frequently Asked Questions</title>

<tcl>
set cnt 1
proc faq {question answer} {
  set ::faq($::cnt) [list [string trim $question] [string trim $answer]]
  incr ::cnt
}

#############
# Enter questions and answers here.

faq {
  How do I create an AUTOINCREMENT field.
} {
  <p>Short answer: A column declared [INTEGER PRIMARY KEY] will
  autoincrement.</p>

  <p>Longer answer:
  If you declare a column of a table to be [INTEGER PRIMARY KEY], then
  whenever you insert a NULL

simply by cloning the official repository:</p>

<blockquote><pre>
fossil clone http://www.sqlite.org/src private-project.fossil
</pre></blockquote>

<p>This command both creates the new repository and populates it with
all the latest SQLite could.  You can the create a private branch as
described in section 3.4.</p>

<p>When the private repository is created by cloning, incorporating new
public SQLite releases becomes much easier too.  To pull in all of the
latest changes from the public SQLite repository, simply move into
the open check-out and do:</p>

The total amount of data written is around three times the size of the
final database file. By contrast, an RBU Vacuum requires roughly the size
of the final database file in temporary disk space and writes a total of
twice that to disk.

<p>On the other hand, an RBU Vacuum uses more CPU than a regular SQLite
VACUUM - in one test as much as five times as much. For this reason, an RBU
Vaccum is often significantly slower than an SQLite VACUUM under the same
conditions.

<li><b>RBU runs in the background</b>

<p>An ongoing RBU operation (either an update or a vacuum) does not
interfere with read access to the database file.

<li><p>The target database may not contain [indexes on expressions].
<li><p>No other writes may occur on the target database while the
       RBU update is being applied.  A read-lock is held on the target
       database to prevent this.</p></li>
</ul>


<h2>Preparing An RBU Update File</h2>

<p>All changes to be applied by RBU are stored in a separate SQLite database
called the "RBU database".  The database that is to be modified is called
the "target database".

<p>For each table in the target database that will be modified by the update,
a corresponding table is created within the RBU database. The RBU database

<p>is represented by the data_t1 row created by:

<codeblock>
INSERT INTO data_t1(a, b, c, rbu_control) VALUES(4, NULL, 'usa', '..x');
</codeblock>

<p>If RBU is used to update a large BLOB value within a target database, it
may be be more efficient to store a patch or delta that can be used to modify
the existing BLOB instead of an entirely new value within the RBU database. 
RBU allows deltas to be specified in two ways:

<ul>
  <li> In the "fossil delta" format - the format used for blob deltas by the 
  <a href=http://fossil-scm.org>Fossil source-code management system</a>, or

<dd><p>Use the schema-defined [PRIMARY KEY] instead of the [rowid] to
       pair rows in the source and destination database.  (See additional
       explanation below.)</dd>
<dt><b>--schema</b></dt>
<dd><p>Show only differences in the schema not the table content</p></dd>
<dt><b>--summary</b></dt>
<dd><p>Show how many rows have changed on each table, but do not show
       the actual chagnes</dd>
<dt><b>--table TABLE</b></dt>
<dd><p>Show only the differences in content for TABLE, not for the
       entire database</p></dd>
<dt><b>--transaction</b></dt>
<dd><p>Wrap SQL output in a single large transaction</p></dd>
<dt><b>--vtab</b></dt>
<dd><p>Add support for handling [FTS3], [FTS5] and [rtree] virtual tables. 

[CREATE TRIGGER|TRIGGERs] or [CREATE VIEW|VIEWs].

<li><p id=vtab>
By default, differences in the schema or content of virtual tables are
not reported on. 

<p>However, if a [virtual table] implementation creates real tables (sometimes
refered to as "shadow" tables) within the database to store its data in, then
sqldiff.exe does calculate the difference between these. This can have
surprising effects if the resulting SQL script is then run on a database that
is not <i>exactly</i> the same as the source database. For several of SQLite's
bundled virtual tables (FTS3, FTS5, rtree and others), the surprising effects
may include corruption of the virtual table content.

<p> If the --vtab option is passed to sqldiff.exe, then it ignores all 
underlying shadow tables belonging to an FTS3, FTS5 or rtree virtual table
and instead includes the virtual table differences directly.

</ol>