/*

create table t12872 (id integer primary key, c1 char(100));
insert into t12872 values(1, 'abc');
...

http://dev.mysql.com/doc/mysql/en/encryption-functions.html

"The return string is a binary string where the first character is 
CHAR(128 | key_num)."

mysql> explain SELECT AES_DECRYPT(c1, '123') from t12872 order by id limit 1;
+----+-------------+--------+-------+---------------+---------+---------+------+
------+-------+
| id | select_type | table  | type  | possible_keys | key     | key_len | ref  |
 rows | Extra |
+----+-------------+--------+-------+---------------+---------+---------+------+
------+-------+
|  1 | SIMPLE      | t12872 | index | NULL          | PRIMARY |       4 | NULL |
   15 |       |
+----+-------------+--------+-------+---------------+---------+---------+------+
------+-------+
1 row in set (0,00 sec)

mysql> explain SELECT AES_DECRYPT(c1, '123') from t12872 order by id;
+----+-------------+--------+------+---------------+------+---------+------+----
--+----------------+
| id | select_type | table  | type | possible_keys | key  | key_len | ref  | row
s | Extra          |
+----+-------------+--------+------+---------------+------+---------+------+----
--+----------------+
|  1 | SIMPLE      | t12872 | ALL  | NULL          | NULL |    NULL | NULL |   1
5 | Using filesort |
+----+-------------+--------+------+---------------+------+---------+------+----
--+----------------+
1 row in set (0,00 sec)

mysql> explain SELECT AES_DECRYPT(c1, '123') from t12872;
+----+-------------+--------+------+---------------+------+---------+------+----
--+-------+
| id | select_type | table  | type | possible_keys | key  | key_len | ref  | row
s | Extra |
+----+-------------+--------+------+---------------+------+---------+------+----
--+-------+
|  1 | SIMPLE      | t12872 | ALL  | NULL          | NULL |    NULL | NULL |   1
5 |       |
+----+-------------+--------+------+---------------+------+---------+------+----
--+-------+
1 row in set (0,01 sec)


*/

#include <stdio.h>
#include "mysql.h"

#define SELECT1 "SELECT AES_DECRYPT(c1, '123') from t12872 order by id limit 1"
#define SELECT2 "SELECT AES_DECRYPT(c1, '123') from t12872"

int main()
{
  MYSQL *conn;
  MYSQL_STMT *stmt;
  MYSQL_RES *meta;
  MYSQL_FIELD *field;
  MYSQL_BIND bind = {0};
  int res;
  unsigned long len;
  char buf[21] = {0};
  double d=-1.0;

  conn= mysql_init(NULL);
  conn= mysql_real_connect(conn, "127.0.0.1", "root", "", "test", 3306, 0, 0);
  if (!conn) {
    fprintf(stderr, "Cannot connect\n");
    exit(1);
  }

  stmt= mysql_stmt_init(conn);

  res= mysql_stmt_prepare(stmt, SELECT1, strlen(SELECT1));

  meta= mysql_stmt_result_metadata(stmt);
  field= mysql_fetch_field_direct(meta, 0);
  printf("type=%d\n", field->type);
  printf("length=%d\n", field->length);
  printf("decimals=%d\n", field->decimals);
  mysql_free_result(meta);

  res= mysql_stmt_prepare(stmt, SELECT2, strlen(SELECT2));

  meta= mysql_stmt_result_metadata(stmt);
  field= mysql_fetch_field_direct(meta, 0);
  printf("type=%d\n", field->type);
  printf("length=%d\n", field->length);
  printf("decimals=%d\n", field->decimals);
  mysql_free_result(meta);

  mysql_close(conn);
  return 0;
}