Files implementing UDFs must be compiled and installed on the
host where the server runs. This process is described here for
the example UDF file
that is included in MySQL source distributions. For additional
information about UDF installation, see
Section 5.6.1, “Installing and Uninstalling User-Defined Functions”.
If a UDF will be referred to in statements that will be replicated to slave servers, you must ensure that every slave also has the function available. Otherwise, replication fails on the slaves when they attempt to invoke the function.
The immediately following instructions are for Unix. Instructions for Windows are given later in this section.
udf_example.cc file contains the
metaphon()returns a metaphon string of the string argument. This is something like a soundex string, but it is more tuned for English.
myfunc_double()returns the sum of the ASCII values of the characters in its arguments, divided by the sum of the length of its arguments.
myfunc_int()returns the sum of the length of its arguments.
sequence([const int])returns a sequence starting from the given number or 1 if no number has been given.
lookup()returns the IP address for a host name.
reverse_lookup()returns the host name for an IP address. The function may be called either with a single string argument of the form
'xxx.xxx.xxx.xxx'or with four numbers.
avgcost()returns an average cost. This is an aggregate function.
A dynamically loadable file should be compiled as a sharable library file, using a command something like this:
gcc -shared -o udf_example.so udf_example.cc
If you are using gcc with
CMake (which is how MySQL itself is
configured), you should be able to create
udf_example.so with a simpler command:
After compiling a shared object containing UDFs, you must
install it and tell MySQL about it. Compiling a shared object
gcc directly produces a file named
udf_example.so. Copy the shared object to
the server's plugin directory and name it
udf_example.so. This directory is given
by the value of the
plugin_dir system variable.
On some systems, the ldconfig program that
configures the dynamic linker does not recognize a shared
object unless its name begins with
this case you should rename a file such as
On Windows, compile user-defined functions using the following procedure:
Obtain a MySQL source distribution. See Section 2.1.2, “How to Get MySQL”.
Obtain the CMake build utility, if necessary, from http://www.cmake.org. (Version 2.6 or later is required).
In the source tree, look in the
sqldirectory for files named
udf_example.cc. Copy both files from this directory to your working directory.
Create a CMake
CMakeLists.txt) with these contents:
PROJECT(udf_example) # Path for MySQL include directory INCLUDE_DIRECTORIES("c:/mysql/include") ADD_DEFINITIONS("-DHAVE_DLOPEN") ADD_LIBRARY(udf_example MODULE udf_example.cc udf_example.def) TARGET_LINK_LIBRARIES(udf_example wsock32)
Create the VC project and solution files, substituting an appropriate
cmake -G "generator"
Invoking cmake --help shows you a list of valid generators.
devenv udf_example.sln /build Release
On all platforms, after the shared library file has been
copied to the
directory, notify mysqld about the new
functions with the following statements. If library files have
a suffix different from
.so on your
system, substitute the correct suffix throughout (for example,
.dll on Windows).
CREATE FUNCTION metaphon RETURNS STRING SONAME 'udf_example.so'; CREATE FUNCTION myfunc_double RETURNS REAL SONAME 'udf_example.so'; CREATE FUNCTION myfunc_int RETURNS INTEGER SONAME 'udf_example.so'; CREATE FUNCTION sequence RETURNS INTEGER SONAME 'udf_example.so'; CREATE FUNCTION lookup RETURNS STRING SONAME 'udf_example.so'; CREATE FUNCTION reverse_lookup RETURNS STRING SONAME 'udf_example.so'; CREATE AGGREGATE FUNCTION avgcost RETURNS REAL SONAME 'udf_example.so';
Once installed, a function remains installed until it is uninstalled.
To remove functions, use
DROP FUNCTION metaphon; DROP FUNCTION myfunc_double; DROP FUNCTION myfunc_int; DROP FUNCTION sequence; DROP FUNCTION lookup; DROP FUNCTION reverse_lookup; DROP FUNCTION avgcost;
CREATE FUNCTION and
DROP FUNCTION statements update
func table in the
mysql system database that serves as a UDF
registry. The function's name, type and shared library name
are saved in the
mysql.func table. To
create functions, you must have the
INSERT privilege for the
mysql database. To drop functions, you must
DELETE privilege for
You cannnot use
to reinstall a function that has previously been installed. To
reinstall a function, first remove it with
DROP FUNCTION, then install it
CREATE FUNCTION. You would
need to do this, for example, if you upgrade to a new version
of MySQL that provides an updated implementation of the
function, or you recompile a new version of a function that
you have written. Otherwise, the server continues to use the
An active function is one that has been loaded with
CREATE FUNCTION and not removed
DROP FUNCTION. All active
functions are reloaded each time the server starts, unless you
start mysqld with the
--skip-grant-tables option. In
this case, the server does not load UDFs during startup and
UDFs are unavailable.