MySQL Bugs: #3487: use mysql_use_result() functoin also for mysql

Bug #3487	use mysql_use_result() functoin also for mysql_stmt based handling
Submitted:	16 Apr 2004 17:05	Modified:	30 Nov 2009 14:20
Reporter:	wim delvaux	Email Updates:
Status:	Closed	Impact on me:	None
Category:	MySQL Server: C API (client library)	Severity:	S4 (Feature request)
Version:	4.1.2	OS:	Linux (Linux)
Assigned to:		CPU Architecture:	Any

Description:
The mysql_bind_result method of returning data from prepared statements does not 
allow for dynamic behavior. I.e the buffers passed to the bind must be preallocated. 
 
This is difficult for blobs and for strings. 
 
However the mysql_usb_result and fetch_row() seem to be able to handle it by returning 
a MYSQL_FIELD * array. 
 
Would it be possible to create a mysql_stmt_use_result() that converts the result of a 
prepared statement to a result of a non-prepared statement so that API becomes easier 
and better 

How to repeat:
n/A

Yes, now there is no way to find out length of long column before actual fetch.
If you use mysql_stmt_store_result function and buffer entire result set in the statement,
you can use field->max_length for this column from statement result metadata (which can be 
obtained by mysql_stmt_result_metadata).
But this works only if you set STMT_ATTR_UPDATE_MAX_LENGTH attribute of the statement with
recently implemented mysql_stmt_attr_set.

Alternatively you can use mysql_stmt_fetch with buffer for this column of zero length and 
pointer to write real lenght to, followed by mysql_stmt_fetch_column.

Example:
real_length= 0;

bind[0].buffer= 0;
bind[0].buffer_length= 0;
bind[0].length= &real_length
mysql_stmt_bind_result(stmt, bind);

mysql_stmt_fetch(stmt);
if (real_length > 0)
{
  data= malloc(real_length);
  bind[0].buffer= data;
  bind[0].buffer_length= real_length;
  mysql_stmt_fetch_column(stmt, 0, bind, 0);
}

OK thanx for the reply. 
 
Perhaps the documentation should be a be more clear on that 
 
W

I think this is properly documented already. See

http://dev.mysql.com/doc/refman/5.1/en/mysql-stmt-attr-set.html
http://dev.mysql.com/doc/refman/5.1/en/mysql-stmt-fetch.html