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+<!-- keywords: {function creation routines} sqlite3_create_function sqlite3_create_function16 sqlite3_create_function_v2 sqlite3_create_window_function -->
+<div class=nosearch>
+<a href="intro.html"><h2>SQLite C Interface</h2></a>
+<h2>Create Or Redefine SQL Functions</h2>
+</div>
+<blockquote><pre>
+int sqlite3_create_function(
+  sqlite3 *db,
+  const char *zFunctionName,
+  int nArg,
+  int eTextRep,
+  void *pApp,
+  void (*xFunc)(sqlite3_context*,int,sqlite3_value**),
+  void (*xStep)(sqlite3_context*,int,sqlite3_value**),
+  void (*xFinal)(sqlite3_context*)
+);
+int sqlite3_create_function16(
+  sqlite3 *db,
+  const void *zFunctionName,
+  int nArg,
+  int eTextRep,
+  void *pApp,
+  void (*xFunc)(sqlite3_context*,int,sqlite3_value**),
+  void (*xStep)(sqlite3_context*,int,sqlite3_value**),
+  void (*xFinal)(sqlite3_context*)
+);
+int sqlite3_create_function_v2(
+  sqlite3 *db,
+  const char *zFunctionName,
+  int nArg,
+  int eTextRep,
+  void *pApp,
+  void (*xFunc)(sqlite3_context*,int,sqlite3_value**),
+  void (*xStep)(sqlite3_context*,int,sqlite3_value**),
+  void (*xFinal)(sqlite3_context*),
+  void(*xDestroy)(void*)
+);
+int sqlite3_create_window_function(
+  sqlite3 *db,
+  const char *zFunctionName,
+  int nArg,
+  int eTextRep,
+  void *pApp,
+  void (*xStep)(sqlite3_context*,int,sqlite3_value**),
+  void (*xFinal)(sqlite3_context*),
+  void (*xValue)(sqlite3_context*),
+  void (*xInverse)(sqlite3_context*,int,sqlite3_value**),
+  void(*xDestroy)(void*)
+);
+</pre></blockquote>
+<p>
+These functions (collectively known as "function creation routines")
+are used to add SQL functions or aggregates or to redefine the behavior
+of existing SQL functions or aggregates. The only differences between
+the three "sqlite3_create_function*" routines are the text encoding
+expected for the second parameter (the name of the function being
+created) and the presence or absence of a destructor callback for
+the application data pointer. Function sqlite3_create_window_function()
+is similar, but allows the user to supply the extra callback functions
+needed by <a href="../windowfunctions.html#aggwinfunc">aggregate window functions</a>.</p>
+
+<p>The first parameter is the <a href="../c3ref/sqlite3.html">database connection</a> to which the SQL
+function is to be added.  If an application uses more than one database
+connection then application-defined SQL functions must be added
+to each database connection separately.</p>
+
+<p>The second parameter is the name of the SQL function to be created or
+redefined.  The length of the name is limited to 255 bytes in a UTF-8
+representation, exclusive of the zero-terminator.  Note that the name
+length limit is in UTF-8 bytes, not characters nor UTF-16 bytes.
+Any attempt to create a function with a longer name
+will result in <a href="../rescode.html#misuse">SQLITE_MISUSE</a> being returned.</p>
+
+<p>The third parameter (nArg)
+is the number of arguments that the SQL function or
+aggregate takes. If this parameter is -1, then the SQL function or
+aggregate may take any number of arguments between 0 and the limit
+set by <a href="../c3ref/limit.html">sqlite3_limit</a>(<a href="../c3ref/c_limit_attached.html#sqlitelimitfunctionarg">SQLITE_LIMIT_FUNCTION_ARG</a>).  If the third
+parameter is less than -1 or greater than 127 then the behavior is
+undefined.</p>
+
+<p>The fourth parameter, eTextRep, specifies what
+<a href="../c3ref/c_any.html">text encoding</a> this SQL function prefers for
+its parameters.  The application should set this parameter to
+<a href="../c3ref/c_any.html">SQLITE_UTF16LE</a> if the function implementation invokes
+<a href="../c3ref/value_blob.html">sqlite3_value_text16le()</a> on an input, or <a href="../c3ref/c_any.html">SQLITE_UTF16BE</a> if the
+implementation invokes <a href="../c3ref/value_blob.html">sqlite3_value_text16be()</a> on an input, or
+<a href="../c3ref/c_any.html">SQLITE_UTF16</a> if <a href="../c3ref/value_blob.html">sqlite3_value_text16()</a> is used, or <a href="../c3ref/c_any.html">SQLITE_UTF8</a>
+otherwise.  The same SQL function may be registered multiple times using
+different preferred text encodings, with different implementations for
+each encoding.
+When multiple implementations of the same function are available, SQLite
+will pick the one that involves the least amount of data conversion.</p>
+
+<p>The fourth parameter may optionally be ORed with <a href="../c3ref/c_deterministic.html#sqlitedeterministic">SQLITE_DETERMINISTIC</a>
+to signal that the function will always return the same result given
+the same inputs within a single SQL statement.  Most SQL functions are
+deterministic.  The built-in <a href="../lang_corefunc.html#random">random()</a> SQL function is an example of a
+function that is not deterministic.  The SQLite query planner is able to
+perform additional optimizations on deterministic functions, so use
+of the <a href="../c3ref/c_deterministic.html#sqlitedeterministic">SQLITE_DETERMINISTIC</a> flag is recommended where possible.</p>
+
+<p>The fourth parameter may also optionally include the <a href="../c3ref/c_deterministic.html#sqlitedirectonly">SQLITE_DIRECTONLY</a>
+flag, which if present prevents the function from being invoked from
+within VIEWs, TRIGGERs, CHECK constraints, generated column expressions,
+index expressions, or the WHERE clause of partial indexes.</p>
+
+<p>For best security, the <a href="../c3ref/c_deterministic.html#sqlitedirectonly">SQLITE_DIRECTONLY</a> flag is recommended for
+all application-defined SQL functions that do not need to be
+used inside of triggers, view, CHECK constraints, or other elements of
+the database schema.  This flags is especially recommended for SQL
+functions that have side effects or reveal internal application state.
+Without this flag, an attacker might be able to modify the schema of
+a database file to include invocations of the function with parameters
+chosen by the attacker, which the application will then execute when
+the database file is opened and read.</p>
+
+<p>The fifth parameter is an arbitrary pointer.  The implementation of the
+function can gain access to this pointer using <a href="../c3ref/user_data.html">sqlite3_user_data()</a>.</p>
+
+<p>The sixth, seventh and eighth parameters passed to the three
+"sqlite3_create_function*" functions, xFunc, xStep and xFinal, are
+pointers to C-language functions that implement the SQL function or
+aggregate. A scalar SQL function requires an implementation of the xFunc
+callback only; NULL pointers must be passed as the xStep and xFinal
+parameters. An aggregate SQL function requires an implementation of xStep
+and xFinal and NULL pointer must be passed for xFunc. To delete an existing
+SQL function or aggregate, pass NULL pointers for all three function
+callbacks.</p>
+
+<p>The sixth, seventh, eighth and ninth parameters (xStep, xFinal, xValue
+and xInverse) passed to sqlite3_create_window_function are pointers to
+C-language callbacks that implement the new function. xStep and xFinal
+must both be non-NULL. xValue and xInverse may either both be NULL, in
+which case a regular aggregate function is created, or must both be
+non-NULL, in which case the new function may be used as either an aggregate
+or aggregate window function. More details regarding the implementation
+of aggregate window functions are
+<a href="../windowfunctions.html#udfwinfunc">available here</a>.</p>
+
+<p>If the final parameter to sqlite3_create_function_v2() or
+sqlite3_create_window_function() is not NULL, then it is destructor for
+the application data pointer. The destructor is invoked when the function
+is deleted, either by being overloaded or when the database connection
+closes. The destructor is also invoked if the call to
+sqlite3_create_function_v2() fails.  When the destructor callback is
+invoked, it is passed a single argument which is a copy of the application
+data pointer which was the fifth parameter to sqlite3_create_function_v2().</p>
+
+<p>It is permitted to register multiple implementations of the same
+functions with the same name but with either differing numbers of
+arguments or differing preferred text encodings.  SQLite will use
+the implementation that most closely matches the way in which the
+SQL function is used.  A function implementation with a non-negative
+nArg parameter is a better match than a function implementation with
+a negative nArg.  A function where the preferred text encoding
+matches the database encoding is a better
+match than a function where the encoding is different.
+A function where the encoding difference is between UTF16le and UTF16be
+is a closer match than a function where the encoding difference is
+between UTF8 and UTF16.</p>
+
+<p>Built-in functions may be overloaded by new application-defined functions.</p>
+
+<p>An application-defined function is permitted to call other
+SQLite interfaces.  However, such calls must not
+close the database connection nor finalize or reset the prepared
+statement in which the function is running.
+</p><p>See also lists of
+  <a href="objlist.html">Objects</a>,
+  <a href="constlist.html">Constants</a>, and
+  <a href="funclist.html">Functions</a>.</p>
+