UDF of MySQL

In MYSQL, you can use the create function command to call different. so shared library files.

Before compilation, add the following options: -- with-mysqld-ldflags =-rdynamic.

A minor problem occurred during re-compilation, possibly because the system was lost during the upgrade ......

Configure: error: No curses/termcap library found

Solution: sudo apt-get install libncurses5-dev

And then use configure again.

In the SQL folder, there is an instance program udf_example.c file. You can compile the file separately to generate a shared library file:

Gcc-shared-o udf_example.so udf_example.cc-I/usr/local/mysql/include/mysql

 

In the SQL folder, The udf_example.def file provides the function list:

LIBRARY udf_example

VERSION 1.0:

EXPORTS

Lookup

Lookup_init

Reverse_lookup

Reverse_lookup_init

Metaphon_init

Metaphon_deinit

Metaphon

Myfunc_double_init

Myfunc_double

Myfunc_int_init

Myfunc_int

Sequence_init

Sequence_deinit

Sequence

Avgcost_init

Avgcost_deinit

Avgcost_reset

Avgcost_add

Avgcost_clear

Avgcost

Is_const

Is_const_init

Check_const_len

Check_const_len_init

Specifically, xx_init indicates the loading function, and xx_deinit indicates the unmounting function, which corresponds to the create function AND drop function respectively.

Xx_clear: resets or returns the relevant value to zero.

Xx_add: used together with xx_clear to group.

 

Modify the configuration file my. cnf

Add the following line to mysqld: plugin_dir =/usr/local/mysql/lib/plugin. All the shared library files are stored in this folder.

Run the udf_example.so file cp in this folder, open the server, and run: mysql> create function metaphon returns string soname "udf_example.so ";

ERROR: ERROR 1127 (HY000): Can't find symbol 'metaphon' in library

 

The file location in the shared library is correct, and there is no problem with the permissions. I have found a lot on the Internet and have not found the correct answers. I think it may be because an error occurred while compiling the UDF source file, after multiple attempts, the call is successfully compiled in the following format:

Make udf_example.o

Gcc-Wall-shared-DMYSQL_DYNAMIC_PLUGIN udf_example.o-o udf_example.so

Copy udf_example.so to the/usr/local/mysql/lib/plugin folder. The execution is successful:

Mysql> create function metaphon returns string soname "udf_example.so ";

Query OK, 0 rows affected (0.00 sec)