sql query problem in c++ and mysql

hi to all, i've centos 7.5 in VM. I've a problem with sql query. here i want to display product, customer and billing information by a one sql. here is a program.

Code:void classBill::todaySales()
{
mysql = classConn::connection();
mysql->reconnect = true;

draw->clrscr();
draw->drawRect();

draw->gotoxy(15, 3);

cout << "Sales By Date";
draw->gotoxy(13,4);
cout << "-----------------";
draw->gotoxy(10, 5);
cout << "Enter Date to see sale : ( yyyy / MM/ dd ) : ";
do
{
flag = true;
draw->gotoxy(55, 5);
ioctl(STDOUT_FILENO, TIOCGWINSZ, &w);
for(int i = 55; i < w.ws_col -1; i++)
{
cout << " ";
}
draw->gotoxy(55, 5);
getline(cin,strdate);
if(strdate.empty())
{
flag == true;
}
else
{
flag = classValid::isValidDate(strdate);
if(!flag)
{
draw->gotoxy(10, 6);
cout << "invalid date please re-enter";
strdate.clear();
getc->getch();
draw->gotoxy(10, 6);
ioctl(STDOUT_FILENO, TIOCGWINSZ, &w);

for(int i = 10; i < w.ws_col - 1; i++)
{
cout << " ";
}
}
}
}while(flag == false);

if(strdate.empty() == true)
{
date *dt = new date;
time_t now = time(0);
tm *ltm = std::localtime(&now);
dt->yy = ltm->tm_year;
dt->mm = ltm->tm_mon+1;
dt->dd = ltm->tm_mday;

strdate = std::to_string(1900 + dt->yy) + "/" + std::to_string(dt->mm) + "/" + std::to_string(dt->dd);
draw->gotoxy(10, 6);
cout << "date : " << strdate << endl;
}
else
{
draw->gotoxy(10, 6);
cout << "date : " << strdate << endl;
}

mysql = classConn::connection();
// here is sql query
sql = "select p.productname, p.rate, b.quantity, b.total, b.billno, c.customername, c.contactaddress, c.mobileno, c.id as CustomerID from tableProductRecords as p, tableBilling as ";
sql += "b, tableCustomers as c where b.dateofsale = '"+ strdate+"' and p.productname in ( select productname from tableProductRecords where productid = ";
sql += "b.productid ) and c.customername in (select customername from tableCustomers where billno = b.billno) order by b.billno;";

qstate = mysql_query(mysql, sql.c_str());
if(!qstate)
{
res = mysql_store_result(mysql);
lines = sqlp->process_result_set(mysql, res, 10, totallen);
}
else
{
draw->gotoxy(10, 7);
cout << "Error in todays sale : " << mysql_error(mysql);
getc->getch();
return;
}

sql = "select sum(total) from tableBilling where dateofsale = '"+strdate+"';";
mysql = classConn::connection();
qstate = mysql_query(mysql, sql.c_str());
if(!qstate)
{
res = mysql_store_result(mysql);
if((row = mysql_fetch_row(res)) != nullptr)
{
if(row[0] != nullptr)
{
gtotal = std::stoi(row[0]);
}
else
{
gtotal = 0;
}
}
}
else
{
draw->gotoxy(10, lines + 25);
cout << "Error in sum(total) : " << mysql_error(mysql);
getc->getch();
}

draw->gotoxy(10, lines + 15);
cout << "Grand total : " << gtotal;

getc->getch();
}now problem is that sql query returns unwanted rows. as in these pics. here cutomer id "2" is not included in billno = 18, customer id 2 is having bill no 2 not 18 butit customerid 2 is showing in billno with 18. how to get only rows that have correct billno and customer id.
Attached Thumbnails