How to check if there is no more rows to fetched using libpq?

Question

I am using C++ and using libpq to access PostgreSQL. I am a newbie to libpq and need to process data of table row by row. below is snippet of code

 PGresult* res = PQexec(conn, "DECLARE myCursor CURSOR FOR select * from my_table");
   if (PQresultStatus(res) != PGRES_COMMAND_OK)
   {
     fprintf(stderr, "DECLARE CURSOR failed: %s", PQerrorMessage(conn));
     PQclear(res);
     exit(1);
   }
   PQclear(res);
   while (true) // need a break condition till data is in cursor
  {
     res = PQexec(conn, "FETCH NEXT in myCursor");
     if (PQresultStatus(res) != PGRES_TUPLES_OK)
    {
      //error handling code and break
    }
     if(PQntuples(res) ==0)
        break;
    //handle the query result
   }

Is there a way to check that we have fetched all records and there is no more record left to fetch. Currently I am relying upon

PQresultStatus(res) != PGRES_TUPLES_OK and PQntuples(res) == 0

Fetch is useful when there is a huge no of rows in db. – Rakesh Mehta Apr 26 '23 at 14:46 — Rakesh Mehta, Apr 26 '23 at 14:46

score 0 · Answer 1 · answered Apr 26 '23 at 14:43

0

when PQntuples(res) is 0 or lesser than the number of rows you try to fetch it means no more data to be fetched.

answered Apr 26 '23 at 14:43

Rakesh Mehta

35
5

How to check if there is no more rows to fetched using libpq?

1 Answers1