mysql query with C - mysql

Question

I am writing a program where the user is giving random 10 bytes which I am storing in a buffer. Then search the hexadecimal string in a MySql database.
unsigned char buffer[10]; //Example:- {23, 181, 185, 192, 101, 156, 61, 247, 206, 204}
//convert each byte into 2 digit hexadecimal characters and store it in an array.
unsigned char hex_bytes[21];
for(int i = 0, l = 0; i < 10; i++) {
int decimal_num = buffer[i];
int quotient, remainder;
char hex_num[10];
quotient = decimal_num;
int j = 0;
while(quotient != 0) {
remainder = quotient % 16;
if(remainder < 10) {
hex_num[j++] = 48 + remainder;
}
else {
hex_num[j++] = 87 + remainder; //hex_num[j++] = 55 + remainder;
}
quotient = quotient/16;
}
for(int k = j-1; k >=0; k--) {
hex_bytes[l++] = hex_num[k];
}
}
printf("Ticket no. = %s\n", hex_bytes);
//------------------------------------------------------------------//
//Querying the Database
unsigned char query1[256];
uint32_t nos[10000];
MYSQL_RES *result;
//unsigned char* hex_str = "17b5b9c0659c3df7cecc"; <-----
//sprintf(query1, "SELECT sn FROM fixit_log WHERE rn = '%s'", hex_str); <-----
sprintf(query1, "SELECT sn FROM fixit_log WHERE rn = '%s'", hex_bytes);
mysql_query(con, query1);
if(mysql_errno(con) != 0) {
printf("stderr: %s\n", mysql_error(con));
mysql_close(con);
return;
}
result = mysql_store_result(con);
int k = 0;
for(int i =0; i < sr_nos_size; i++) {
MYSQL_ROW row = mysql_fetch_row(result);
printf("--sn: %2s\n", row[0]);
}
}
My Database looks like this:
sn rn
123456 17b5b9c0659c3df7cecc ///hexadecimal string of the given example as stored in the database
123457 17b5b9c0659c3df7cecc
123458 17b5b9c0659c3df7cecc
If I hardcode the hexadecimal string(comment out // part), I am getting the proper output. But if I run the program as above I am don't get any output.