## Run this Tcl script to generate the autoinc.html file.#set rcsid {$Id: }source common.tclif {[llength $argv]>0} {  set outputdir [lindex $argv 0]} else {  set outputdir ""}header {SQLite Autoincrement}puts {<h1>SQLite Autoincrement</h1><p>In SQLite, every row of every table has an integer ROWID.The ROWID for each row is unique among all rows in the same table.In SQLite version 2.8 the ROWID is a 32-bit signed integer.Version 3.0 of SQLite expanded the ROWID to be a 64-bit signed integer.</p><p>You can access the ROWID of an SQLite table using one the special columnnames ROWID, _ROWID_, or OID.Except if you declare an ordinary table column to use one of those specialnames, then the use of that name will refer to the declared column notto the internal ROWID.</p><p>If a table contains a column of type INTEGER PRIMARY KEY, then thatcolumn becomes an alias for the ROWID.  You can then access the ROWIDusing any of four different names, the original three names described aboveor the name given to the INTEGER PRIMARY KEY column.  All these names arealiases for one another and work equally well in any context.</p><p>When a new row is inserted into an SQLite table, the ROWID can eitherbe specified as part of the INSERT statement or it can be assignedautomatically by the database engine.  To specify a ROWID manually,just include it in the list of values to be inserted.  For example:</p><blockquote><pre>CREATE TABLE test1(a INT, b TEXT);INSERT INTO test1(rowid, a, b) VALUES(123, 5, 'hello');</pre></blockquote><p>If no ROWID is specified on the insert, an appropriate ROWID is createdautomatically.  The usual algorithm is to give the newly created rowa ROWID that is one larger than the largest ROWID in the table priorto the insert.  If the table is initially empty, then a ROWID of 1 isused.  If the largest ROWID is equal to the largest possible integer(9223372036854775807 in SQLite version 3.0 and later) then the databaseengine starts picking candidate ROWIDs at random until it finds onethat is not previously used.</p><p>The normal ROWID selection algorithm described abovewill generate monotonically increasingunique ROWIDs as long as you never use the maximum ROWID value and you neverdelete the entry in the table with the largest ROWID. If you ever delete rows or if you ever create a row with the maximum possibleROWID, then ROWIDs from previously deleted rows might be reused when creatingnew rows and newly created ROWIDs might not be in strictly accending order.</p><h2>The AUTOINCREMENT Keyword</h2><p>If a column has the type INTEGER PRIMARY KEY AUTOINCREMENT then a slightlydifferent ROWID selection algorithm is used.  The ROWID chosen for the new row is one larger than the largest ROWIDthat has ever before existed in that same table.  If the table has neverbefore contained any data, then a ROWID of 1 is used.  If the tablehas previously held a row with the largest possible ROWID, then new INSERTsare not allowed and any attempt to insert a new row will fail with anSQLITE_FULL error.</p><p>SQLite keeps track of the largest ROWID that a table has ever held usingthe special SQLITE_SEQUENCE table.  The SQLITE_SEQUENCE table is createdand initialized automatically whenever a normal table that contains anAUTOINCREMENT column is created.  The content of the SQLITE_SEQUENCE tablecan be modified using ordinary UPDATE, INSERT, and DELETE statements.But making modifications to this table will likely perturb the AUTOINCREMENTkey generation algorithm.  Make sure you know what you are doing beforeyou undertake such changes.</p><p>The behavior implemented by the AUTOINCREMENT keyword is subtly differentfrom the default behavior.  With AUTOINCREMENT, rows with automaticallyselected ROWIDs are guaranteed to have ROWIDs that have never been usedbefore by the same table in the same database.  And the automatically generatedROWIDs are guaranteed to be monotonically increasing.  These are importantproperties in certain applications.  But if your application does notneed these properties, you should probably stay with the default behaviorsince the use of AUTOINCREMENT requires additional work to be doneas each row is inserted and thus causes INSERTs to run a little slower.}footer $rcsid