Fetching Data

Fetching data from a result set
If the execution of the statement went fine you are now able to fetch the data column by column. May be you would first like to know how many columns there are in the result set (if you use a `SELECT * FROM tkeyuser` you wouldn't know in your program). A call to `SQLNumResultCols`. This function takes the statement handle and a pointer to an integer variable which will yield the number of columns after the call. Knowing that much we can add this to our program: `
    // At the beginning add:
    SQLSMALLINT      V_OD_colanz;    // Num of columns

    // At the end add:
       V_OD_erg=SQLNumResultCols(V_OD_hstmt,&V_OD_colanz);
       if ((V_OD_erg != SQL_SUCCESS) &&
           (V_OD_erg != SQL_SUCCESS_WITH_INFO))
          {
           printf("Fehler im ResultCols %d\n",V_OD_erg);
           SQLFreeHandle(SQL_HANDLE_STMT,V_OD_hstmt);
           SQLFreeHandle(SQL_HANDLE_DBC,V_OD_hdbc);
           SQLFreeHandle(SQL_HANDLE_ENV, V_OD_Env);
           exit(0);
          }
       printf("Number of Columns %d\n",V_OD_colanz);
` The next thing you need to know is how many rows have been returned by the query. A call to `SQLRowCount` should quench your thirst for knowledge. The last thing to do is to fetch the data itself from the result set. You should call `SQLFetch` with a statement handle (which has been allocated and `SQLBind` has been called for all columns). `SQLFetch` returns `SQL_NO_DATA` if there is no more data in the result set. So here is the complete source code. Real C-programmers will moan in disgust how inefficient the program is coded, but I prefer it that way (doesn't it look a little bit like PASCAL?). Take it as a starting point for your own endeavors with ODBC. `
    /* odbc.c

        testing unixODBC
    */
    #include <stdlib.h>
    #include <stdio.h>
    #include <odbc/sql.h>
    #include <odbc/sqlext.h>
    #include <odbc/sqltypes.h>

    SQLHENV			 V_OD_Env;			// Handle ODBC environment
    long			 V_OD_erg;			// result of functions
    SQLHDBC			 V_OD_hdbc;			// Handle connection

    char			 V_OD_stat[10];		// Status SQL
    SQLINTEGER		 V_OD_err,V_OD_rowanz,V_OD_id;
    SQLSMALLINT		 V_OD_mlen,V_OD_colanz;
    char             V_OD_msg[200],V_OD_buffer[200];

    int main(int argc,char *argv[])
    {
    	// 1. allocate Environment handle and register version
    	V_OD_erg=SQLAllocHandle(SQL_HANDLE_ENV,SQL_NULL_HANDLE,&V_OD_Env);
    	if ((V_OD_erg != SQL_SUCCESS) && (V_OD_erg != SQL_SUCCESS_WITH_INFO))
    	{
    		printf("Error AllocHandle\n");
    		exit(0);
    	}
    	V_OD_erg=SQLSetEnvAttr(V_OD_Env, SQL_ATTR_ODBC_VERSION, (void*)SQL_OV_ODBC3, 0);
    	if ((V_OD_erg != SQL_SUCCESS) && (V_OD_erg != SQL_SUCCESS_WITH_INFO))
    	{
    		printf("Error SetEnv\n");
    		SQLFreeHandle(SQL_HANDLE_ENV, V_OD_Env);
    		exit(0);
    	}
    	// 2. allocate connection handle, set timeout
    	V_OD_erg = SQLAllocHandle(SQL_HANDLE_DBC, V_OD_Env, &V_OD_hdbc);
    	if ((V_OD_erg != SQL_SUCCESS) && (V_OD_erg != SQL_SUCCESS_WITH_INFO))
    	{
    		printf("Error AllocHDB %d\n",V_OD_erg);
    		SQLFreeHandle(SQL_HANDLE_ENV, V_OD_Env);
    		exit(0);
    	}
    	SQLSetConnectAttr(V_OD_hdbc, SQL_LOGIN_TIMEOUT, (SQLPOINTER *)5, 0);
    	// 3. Connect to the datasource "web"
    	V_OD_erg = SQLConnect(V_OD_hdbc, (SQLCHAR*) "web", SQL_NTS,
                                         (SQLCHAR*) "christa", SQL_NTS,
                                         (SQLCHAR*) "", SQL_NTS);
    	if ((V_OD_erg != SQL_SUCCESS) && (V_OD_erg != SQL_SUCCESS_WITH_INFO))
    	{
    		printf("Error SQLConnect %d\n",V_OD_erg);
    		SQLGetDiagRec(SQL_HANDLE_DBC, V_OD_hdbc,1,
    		              V_OD_stat, &V_OD_err,V_OD_msg,100,&V_OD_mlen);
    		printf("%s (%d)\n",V_OD_msg,V_OD_err);
    		SQLFreeHandle(SQL_HANDLE_ENV, V_OD_Env);
    		exit(0);
    	}
    	printf("Connected !\n");
    	V_OD_erg=SQLAllocHandle(SQL_HANDLE_STMT, V_OD_hdbc, &V_OD_hstmt);
    	if ((V_OD_erg != SQL_SUCCESS) && (V_OD_erg != SQL_SUCCESS_WITH_INFO))
    	{
    		printf("Fehler im AllocStatement %d\n",V_OD_erg);
    		SQLGetDiagRec(SQL_HANDLE_DBC, V_OD_hdbc,1, V_OD_stat,&V_OD_err,V_OD_msg,100,&V_OD_mlen);
    		printf("%s (%d)\n",V_OD_msg,V_OD_err);
    		SQLFreeHandle(SQL_HANDLE_ENV, V_OD_Env);
    		exit(0);
    	}
        SQLBindCol(V_OD_hstmt,1,SQL_C_CHAR, &V_OD_buffer,150,&V_OD_err);
        SQLBindCol(V_OD_hstmt,2,SQL_C_ULONG,&V_OD_id,150,&V_OD_err);

        V_OD_erg=SQLExecDirect(V_OD_hstmt,"SELECT dtname,iduser FROM tkeyuser order by iduser",SQL_NTS);
        if ((V_OD_erg != SQL_SUCCESS) && (V_OD_erg != SQL_SUCCESS_WITH_INFO))
        {
           printf("Error in Select %d\n",V_OD_erg);
           SQLGetDiagRec(SQL_HANDLE_DBC, V_OD_hdbc,1, V_OD_stat,&V_OD_err,V_OD_msg,100,&V_OD_mlen);
           printf("%s (%d)\n",V_OD_msg,V_OD_err);
           SQLFreeHandle(SQL_HANDLE_STMT,V_OD_hstmt);
           SQLFreeHandle(SQL_HANDLE_DBC,V_OD_hdbc);
           SQLFreeHandle(SQL_HANDLE_ENV, V_OD_Env);
           exit(0);
        }
        V_OD_erg=SQLNumResultCols(V_OD_hstmt,&V_OD_colanz);
        if ((V_OD_erg != SQL_SUCCESS) && (V_OD_erg != SQL_SUCCESS_WITH_INFO))
        {
            SQLFreeHandle(SQL_HANDLE_STMT,V_OD_hstmt);
            SQLDisconnect(V_OD_hdbc);
            SQLFreeHandle(SQL_HANDLE_DBC,V_OD_hdbc);
            SQLFreeHandle(SQL_HANDLE_ENV, V_OD_Env);
            exit(0);
        }
        printf("Number of Columns %d\n",V_OD_colanz);
        V_OD_erg=SQLRowCount(V_OD_hstmt,&V_OD_rowanz);
        if ((V_OD_erg != SQL_SUCCESS) && (V_OD_erg != SQL_SUCCESS_WITH_INFO))
        {
          printf("Number ofRowCount %d\n",V_OD_erg);
          SQLFreeHandle(SQL_HANDLE_STMT,V_OD_hstmt);
          SQLDisconnect(V_OD_hdbc);
          SQLFreeHandle(SQL_HANDLE_DBC,V_OD_hdbc);
          SQLFreeHandle(SQL_HANDLE_ENV, V_OD_Env);
          exit(0);
        }
        printf("Number of Rows %d\n",V_OD_rowanz);
        V_OD_erg=SQLFetch(V_OD_hstmt);
        while(V_OD_erg != SQL_NO_DATA)
        {
         printf("Result: %d %s\n",V_OD_id,V_OD_buffer);
         V_OD_erg=SQLFetch(V_OD_hstmt);
        }  ;
        SQLFreeHandle(SQL_HANDLE_STMT,V_OD_hstmt);
        SQLDisconnect(V_OD_hdbc);
        SQLFreeHandle(SQL_HANDLE_DBC,V_OD_hdbc);
        SQLFreeHandle(SQL_HANDLE_ENV, V_OD_Env);
        return(0);
    }
` If I find some more time I will add something about diagnostics, cursor positioning updating and and and...