(mysql.info.gz) UDF arguments

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 25.2.2.3 Argument Processing
 ............................
 
 The `args' parameter points to a `UDF_ARGS' structure that has the
 members listed here:
 
 `unsigned int arg_count'
      The number of arguments.  Check this value in the initialization
      function if you want your function to be called with a particular
      number of arguments.  For example:
 
           if (args->arg_count != 2)
           {
               strcpy(message,"XXX() requires two arguments");
               return 1;
           }
 
 `enum Item_result *arg_type'
      The types for each argument.  The possible type values are
      `STRING_RESULT', `INT_RESULT', and `REAL_RESULT'.
 
      To make sure that arguments are of a given type and return an
      error if they are not, check the `arg_type' array in the
      initialization function.  For example:
 
           if (args->arg_type[0] != STRING_RESULT ||
               args->arg_type[1] != INT_RESULT)
           {
               strcpy(message,"XXX() requires a string and an integer");
               return 1;
           }
 
      As an alternative to requiring your function's arguments to be of
      particular types, you can use the initialization function to set
      the `arg_type' elements to the types you want.  This causes MySQL
      to coerce arguments to those types for each call to `xxx()'.  For
      example, to specify coercion of the first two arguments to string
      and integer, do this in `xxx_init()':
 
           args->arg_type[0] = STRING_RESULT;
           args->arg_type[1] = INT_RESULT;
 
 `char **args'
      `args->args' communicates information to the initialization
      function about the general nature of the arguments your function
      was called with.  For a constant argument `i', `args->args[i]'
      points to the argument value.  (See below for instructions on how
      to access the value properly.)  For a non-constant argument,
      `args->args[i]' is `0'.  A constant argument is an expression that
      uses only constants, such as `3' or `4*7-2' or `SIN(3.14)'.  A
      non-constant argument is an expression that refers to values that
      may change from row to row, such as column names or functions that
      are called with non-constant arguments.
 
      For each invocation of the main function, `args->args' contains the
      actual arguments that are passed for the row currently being
      processed.
 
      Functions can refer to an argument `i' as follows:
 
         * An argument of type `STRING_RESULT' is given as a string
           pointer plus a length, to allow handling of binary data or
           data of arbitrary length.  The string contents are available
           as `args->args[i]' and the string length is
           `args->lengths[i]'.  You should not assume that strings are
           null-terminated.
 
         * For an argument of type `INT_RESULT', you must cast
           `args->args[i]' to a `long long' value:
 
                long long int_val;
                int_val = *((long long*) args->args[i]);
 
         * For an argument of type `REAL_RESULT', you must cast
           `args->args[i]' to a `double' value:
 
                double    real_val;
                real_val = *((double*) args->args[i]);
 
 `unsigned long *lengths'
      For the initialization function, the `lengths' array indicates the
      maximum string length for each argument. You should not change
      these.  For each invocation of the main function, `lengths'
      contains the actual lengths of any string arguments that are
      passed for the row currently being processed.  For arguments of
      types `INT_RESULT' or `REAL_RESULT', `lengths' still contains the
      maximum length of the argument (as for the initialization
      function).
 

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(mysql.info.gz) UDF aggr

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