Question

NSString *cityInput = cityField.text;
NSString *code = @"";
NSString *query = @"SELECT code FROM country WHERE cityname = UPPER(?)";
sqlite3_stmt *statement;
if (sqlite3_prepare_v2(database, [query UTF8String],-1, &statement, nil) == SQLITE_OK)
{
    sqlite3_bind_text(statement, 1, [cityInput UTF8String], -1, SQLITE_STATIC);
    while(sqlite3_step(statement) == SQLITE_ROW) {
        code = [NSString stringWithUTF8String:(char *)sqlite3_column_text(statement, 0)];
    }
} 
if(sqlite3_step(statement) != SQLITE_DONE){
    NSLog(@"DB: query KO");
    UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"ALERT" message:@"City not found" delegate:nil cancelButtonTitle:nil otherButtonTitles:@"OK", nil];
    [alertView show];
    return;
}

sqlite3_close(database);

Two questions:

1) for get single row i must use while loop?

2) if there isn’t result in the query how alert “city not found”

Answer 1

1. Using while gives you the last row and it is not needed. Add limit 1 clause to your query, or simply take the first row returned;
2. Decide whether to show alert by checking return code.