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From:David Godsey Date:March 31 2006 4:39pm
Subject:Re: Is there anyway to return an array?
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So, in theory this should be pretty straight forward to do right?  Well
I'm new to UDF's, so how mysql is passing the data to the UDF is a bit of
a mystery.  I'm hoping someone can help me understand this.

I'm selecting data from a BLOB field like this:

			SELECT payload_time,
			CEIL((flength + (foffset %8 ))/8))
			FROM RawMajorFrames
			WHERE raw_major_frame_id=rfid
			INTO ptime,fdata;

You can see that I'm only taking a portion of the string, but it is still
in raw form.

Now I would like to pass it to my UDF function called toDoubleArray, to
convert each 8 byte section to a double.

I call the function like this: (you can ignore conv_param)
SELECT toDoubleArray(fdata,"%1.3E",conv_param) INTO fdata_string;

Well, I get a Lost Connection when the function is called.
Here is the UDF:

my_bool toDoubleArray_init(UDF_INIT *initid, UDF_ARGS *args, char *message)
  if (args->arg_count != 3)
		strcpy(message,"Wrong arguments to toDouble:  should be
    return 1;
	initid->max_length = strlen(args->args[0])/8 * 128;
  return 0;

char * toDoubleArray(UDF_INIT *initid, UDF_ARGS *args, char *result,
				unsigned long *length,char *is_null,char *error)
	int curr_buf_ptr =0; /* current length of FloatString */
	char * data = args->args[0]; /* just to make it easier to reference the
string */
	char * f = args->args[1];   /* get the format string */
   char format[15];

	sprintf(format,"%s,",f); /* put a comma at the end of format for CSV
format */

	for(int i=0;i<strlen(data);i +=8){
		sprintf(result + curr_buf_ptr,format,*((double *)(data +i)));
		curr_buf_ptr = strlen(result);
	result[curr_buf_ptr -1] = '\0';
	*length = strlen(result);
	return result;
This should return a comma delimited list of double values in a string
format (ascii representation).

Like I said, I'm new to UDF's so it is likely I'm not aware of conventions
to follow that are well known to others.

Any help would be great.

David Godsey

> David Godsey wrote:
>>> I know, I know, sounds like something that should be done in the
>>> presentation layer, howerver if possible, I would like to provide
>>> common
>>> data presentation to multiple presentation layers (written in different
>>> languages).
>>> So is there anyway to return an array in mysql?
> Your aware your doing something stupid and want to do it anyway :-(
> Why not return the values from your user defined mysql function as a
> (properly quoted) ,comma seperated list. Since almost every application
> language now has a standard csv file handling library it should be easy
> to use across diverse display technologies.
> Urrgh
> Nigel

Accomplishing the impossible means only that the boss will add it to your
regular duties.

David Godsey

Is there anyway to return an array?David Godsey24 Mar
  • Re: Is there anyway to return an array?SGreen24 Mar
  • Re: Is there anyway to return an array?Peter Brawley25 Mar
    • Re: Is there anyway to return an array?nigel wood25 Mar
      • Re: Is there anyway to return an array?David Godsey29 Mar
      • Re: Is there anyway to return an array?David Godsey31 Mar
        • Re: Is there anyway to return an array?David Godsey31 Mar