DB_GetFieldIntByName

// examples.inc

// ...

Examples_CalculateSum(DB:dbConnectionHandle)
{
    // Return value variable
    new ret;

    // Database result set
    new DBResult:db_result_set = DB_ExecuteQuery("SELECT `value` FROM `examples`");

    // If database result set is valid
    if (db_result_set)
    {
        // Do operations
        do
        {
            // Add value from "example" field to the return value variable
            ret += DB_GetFieldIntByName(db_result_set, "value");
        }

        // While next row could be fetched
        while (DB_SelectNextRow(db_result_set));

        // Free result set
        DB_FreeResultSet(db_result_set);
    }

    // Return calculated sum
    return ret;
}

// mode.pwn

// ...

#include <examples>

static DB:gDBConnectionHandle;

// ...

public OnGameModeInit()
{
    // ...

    // Create a connection to a database
    gDBConnectionHandle = DB_Open("example.db");

    // If connection to the database exists
    if (gDBConnectionHandle)
    {
        // Successfully created a connection to the database
        print("Successfully created a connection to database \"example.db\".");
        printf("Calculated sum: %d", Examples_CalculateSum(gDBConnectionHandle));
    }
    else
    {
        // Failed to create a connection to the database
        print("Failed to open a connection to database \"example.db\".");
    }

    // ...

    return 1;
}

public OnGameModeExit()
{
    // Close the connection to the database if connection is open
    if (DB_Close(gDBConnectionHandle))
    {
        // Extra cleanup
        gDBConnectionHandle = DB:0;
    }

    // ...

    return 1;
}