Errors while creating a UDF function in MySQL

I am trying to create a UDF function for MySQL (a C function performed by MySQL) and I am facing left and right issues. I'm just going to give you the code. I have a file levenshtein.c

that includes the following declarations and corresponding implementations:

my_bool     sql_levenshtein_init(UDF_INIT *initid, UDF_ARGS *args, char *message);
void        sql_levenshtein_deinit(UDF_INIT *initid);
longlong    sql_levenshtein(UDF_INIT *initid, UDF_ARGS *args, char *is_null, char *error);


I will compile the file (against std = c99 and for arch = i386 if needed). I copy the generated .so file to my mysql plugin folder. I go to mysql and execute the command

mysql> create function sql_levenshtein returns int soname '';


Instead of this command successfully creating this function, I am getting this error

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


In trying to solve the problem, I haven't come up with a lot of useful information. After googling, I used the command nm

to look at the .so file. And I got this output:

00001600 t ___inline_memset_chk
00001870 t ___inline_strcpy_chk
         U ___memset_chk
         U ___stack_chk_fail
         U ___stack_chk_guard
         U ___strcpy_chk
00001220 T _cell_value
         U _free
00001180 T _is_levenshtein_within_normthresh
00001100 T _is_levenshtein_within_thresh
00001460 T _levenshtein
00000cf0 T _levenshtein_k
         U _malloc
00001400 t _minimum
00001660 T _normlevenshtein
000018f0 T _sql_levenshtein
000018c0 T _sql_levenshtein_deinit
00001710 T _sql_levenshtein_init
00001df0 T _sql_levenshtein_within_normthreshold
00001dd0 T _sql_levenshtein_within_normthreshold_deinit
00001d00 T _sql_levenshtein_within_normthreshold_init
00001c00 T _sql_normlevenshtein
00001be0 T _sql_normlevenshtein_deinit
00001b20 T _sql_normlevenshtein_init
         U dyld_stub_binder


Note _sql_levenshtein

, so the function seems to exist. Not sure what else would be helpful. Thank you for your guidance!


========= Update in response to comment: Well, for what it's worth, I also did

mysql> create function _sql_levenshtein returns int soname '';
ERROR 1127 (HY000): Can't find symbol '_sql_levenshtein' in library


Therefore, this does not seem to be the root cause of the problem. Maybe I missed something.


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1 answer

I don't know if you found your answer, but when you create your function in MySQL, you must use the name of the function you defined. So, if you have a UDF called "my_func_udf" and you have something called My_Func () in your code, in your case, you called it:

 longlong sql_levenshtein(UDF_INIT *initid, UDF_ARGS *args, char *is_null, char *error);


This is where all the magic happens, you have to use the name of this function in your create statement i.e. CREATE FUNCTION My_Func RETURNS (STRING, INTEGER, REAL) SONAME "YOUR FILE NAME".

example from your code above:



You defined something and then call something else, it is your fault.



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