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Overview
Comment:Documentation on the sqlite_offset() SQL function.
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SHA3-256: 4ce0a400c292f97c4115de5a521bdf55eb96856d923924137929f5235476e020
User & Date: drh 2018-01-04 19:28:02
Context
2018-01-08
12:05
Add new documentation file zipfile.in. check-in: 99c2fcc179 user: dan tags: trunk
2018-01-04
19:28
Documentation on the sqlite_offset() SQL function. check-in: 4ce0a400c2 user: drh tags: trunk
19:10
Flesh out the description of shadow tables and the rtreecheck() function in the R*Tree documentation. check-in: 2ccafeedbe user: drh tags: trunk
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       [WITHOUT ROWID] tables.
</ol>
<li> Added the [https://sqlite.org/src/file/ext/misc/btreeinfo.c|sqlite_btreeinfo]
     eponymous virtual table for introspecting and estimating the sizes of
     the btrees in a database.
<li> Enhance the [SQLITE_ENABLE_UPDATE_DELETE_LIMIT] compile-time option so
     that it works for [WITHOUT ROWID] tables.
<li> Provide the sqlite_unsupported_offset(X) SQL function that returns
     the byte offset into the database file to the beginning of the record
     holding value X, when compiling with -DSQLITE_ENABLE_OFFSET_SQL_FUNC.
}

chng {2017-10-24 (3.21.0)} {
<li> Take advantage of the atomic-write capabilities in the 
     [https://en.wikipedia.org/wiki/F2FS|F2FS filesystem] when available, for
     greatly reduced transaction overhead.  This currently requires the
     [SQLITE_ENABLE_BATCH_ATOMIC_WRITE] compile-time option.







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       [WITHOUT ROWID] tables.
</ol>
<li> Added the [https://sqlite.org/src/file/ext/misc/btreeinfo.c|sqlite_btreeinfo]
     eponymous virtual table for introspecting and estimating the sizes of
     the btrees in a database.
<li> Enhance the [SQLITE_ENABLE_UPDATE_DELETE_LIMIT] compile-time option so
     that it works for [WITHOUT ROWID] tables.
<li> Provide the [sqlite_offset(X)] SQL function that returns
     the byte offset into the database file to the beginning of the record
     holding value X, when compiling with [-DSQLITE_ENABLE_OFFSET_SQL_FUNC].
}

chng {2017-10-24 (3.21.0)} {
<li> Take advantage of the atomic-write capabilities in the 
     [https://en.wikipedia.org/wiki/F2FS|F2FS filesystem] when available, for
     greatly reduced transaction overhead.  This currently requires the
     [SQLITE_ENABLE_BATCH_ATOMIC_WRITE] compile-time option.

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  databases generated with this option enabled are prone to
  triggering the
  [https://www.sqlite.org/src/info/e6e962d6b0f06f46e|e6e962d6b0f06f46]
  bug in the [sqlite3_blob_reopen()] interface.  For those reasons,
  this optimization is disabled by default.  However, this optimization
  may be enabled by default in a future release of SQLite.
}












COMPILE_OPTION {SQLITE_ENABLE_PREUPDATE_HOOK} {
  This option enables 
  [sqlite3_preupdate_hook|several new APIs] that provide callbacks
  prior to any change to a [rowid table].  The callbacks can be used
  to record the state of the row before the change occurs.
  <p>The action of the preupdate hook is similar to the







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  databases generated with this option enabled are prone to
  triggering the
  [https://www.sqlite.org/src/info/e6e962d6b0f06f46e|e6e962d6b0f06f46]
  bug in the [sqlite3_blob_reopen()] interface.  For those reasons,
  this optimization is disabled by default.  However, this optimization
  may be enabled by default in a future release of SQLite.
}

COMPILE_OPTION {SQLITE_ENABLE_OFFSET_SQL_FUNC} {
  This option enables support for the [sqlite_offset(X)] SQL function.
  <p>
  The [sqlite_offset(X)] SQL function requires a new interface on the
  B-tree storage engine, a new opcode in the [virtual machine] that
  runs SQL statements, and a new conditional in a critical path of the
  code generator.  To avoid that overhead in applications that do not
  need the utility of sqlite_offset(X), the function is disabled by
  default.
}

COMPILE_OPTION {SQLITE_ENABLE_PREUPDATE_HOOK} {
  This option enables 
  [sqlite3_preupdate_hook|several new APIs] that provide callbacks
  prior to any change to a [rowid table].  The callbacks can be used
  to record the state of the row before the change occurs.
  <p>The action of the preupdate hook is similar to the

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  ^The sqlite_compileoption_used() SQL function is a wrapper around the
  [sqlite3_compileoption_used()] C/C++ function.
  ^When the argument X to sqlite_compileoption_used(X) is a string which
  is the name of a compile-time option, this routine returns true (1) or
  false (0) depending on whether or not that option was used during the
  build.
}
















funcdef {sqlite_source_id()} {} {
  ^The sqlite_source_id() function returns a string that identifies the
  specific version of the source code that was used to build the SQLite
  library.  ^The string returned by sqlite_source_id() is
  the date and time that the source code was checked in followed by
  the SHA1 hash for that check-in.  ^This function is







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  ^The sqlite_compileoption_used() SQL function is a wrapper around the
  [sqlite3_compileoption_used()] C/C++ function.
  ^When the argument X to sqlite_compileoption_used(X) is a string which
  is the name of a compile-time option, this routine returns true (1) or
  false (0) depending on whether or not that option was used during the
  build.
}

funcdef {sqlite_offset(X)} {} {
  ^The sqlite_offset(X) function returns the byte offset in the database
  file for the beginning of the record from which value would be read.
  If X is not a column in an ordinary table, then sqlite_offset(X) returns
  NULL.  The value returned by sqlite_offset(X) might reference either the
  original table or an index, depending on the query.  If the value X would
  normally be extracted from an index, the sqlite_offset(X) returns the
  offset to the corresponding index record.  If the value X would be
  extracted from the original table, then sqlite_offset(X) returns the offset
  to the table record.

  <p>The sqlite_offset(X) SQL function is only available if SQLite is built
  using the [-DSQLITE_ENABLE_OFFSET_SQL_FUNC] compile-time option.
}

funcdef {sqlite_source_id()} {} {
  ^The sqlite_source_id() function returns a string that identifies the
  specific version of the source code that was used to build the SQLite
  library.  ^The string returned by sqlite_source_id() is
  the date and time that the source code was checked in followed by
  the SHA1 hash for that check-in.  ^This function is