My program reads 0 from the database even though there is a 1 - c++

Question

I don't understand whats wrong with the code, I have read a lot of times but I can't find the error
pstmt = con->prepareStatement("SELECT (?) FROM votos WHERE id = (?)");
pstmt->setString(1, eleccion);
pstmt->setInt(2, p->getId());
res = pstmt->executeQuery();
while(res->next())
{
p->setVoto(res->getInt(1));
}
When the eleccion and id variables are Provincial and 1 respectively the getInt(1) function should return 1, but it returns 0.
The command (in the mysql command line):
SELECT Provincial from Votos WHERE id=1
Returns a table with one row and one column with the value 1
Side notes:
Spelling was checked
The getId() function works correctly
The compiler doesn't give any error

Answer 1

You can't use a placeholder in a prepared query for a column name. It's returning the value of the string eleccion, not using it as the name of a column in the table. You need to do string concatenation to substitute the column name.
std::string sql = std::string("SELECT `") + eleccion + "` FROM votos WHERE id = ?";
pstmt = con->prepareStatement(sql.c_str());
pstmt->setInt(1, p->getId());
res = pstmt->executeQuery();
while(res->next())
{
p->setVoto(res->getInt(1));
}
If the value of eleccion is coming from the user or some other untrusted source, make sure you validate it before concatenating, to prevent SQL injection.