FMDB Result set contains null iphone

I am using FMDB for my application to store data in sqlite. Here is my code

from AppDelegate

- (void)applicationDidFinishLaunching:(UIApplication *)application 

{

FMDatabase* db = [FMDatabase databaseWithPath:@"/tmp/sql.sqlite"];

if (![db open]) {
    NSLog(@"Could not open db.");

}
NSLog(@"DB opened successfully");

// full code not shown here

}

I have following code in ViewController

-(IBAction)insertButtonClicked:(id)sender

{ NSLog(@"in insertButtonCLicked");

[db beginTransaction];

[db executeUpdate:@"insert into sample (url) values (?)",@"google'"];

[db commit];

}

-(IBAction)displayButtonClicked:(id)sender

{

NSLog(@"in DisplayCLicked");

FMResultSet *rs = [db executeQuery:@"select url from sample"];

NSLog(@"Rs contains => %@",rs);

while( [rs next])
{

    NSLog(@"%@",[rs stringForColumn:@"url"]);
}
[rs close];

}

When i run this code i get rs as null as shown in following (t开发者_如何学Chis is o/p from console)

2011-03-07 07:30:06.919 InsertDataSample[3092:20b] DB opened successfully

2011-03-07 07:30:13.341 InsertDataSample[3092:20b] in insertButtonCLicked

2011-03-07 07:30:16.860 InsertDataSample[3092:20b] in DisplayCLicked

2011-03-07 07:30:16.860 InsertDataSample[3092:20b] Rs contains => (null)

Plz help me friends. I am working on FMDB from many days but i am unable to use FMDB . Thanks in advance

Insert this just after your query and FMDB will probably tell you exactly what the problem is.

if ([db hadError]) {
    NSLog(@"DB Error %d: %@", [db lastErrorCode], [db lastErrorMessage]);
}

Update:

Running this:

FMDatabase *db = [FMDatabase databaseWithPath:@"/tmp/sql.sqlite"];
[db executeUpdate:@"create table sample (url TEXT);"];
[db executeUpdate:@"insert into sample (url) values(?);", @"google'"];
FMResultSet *rs = [db executeQuery:@"select url from sample;"];
while ([rs next]) {
    NSLog(@"%@", [rs stringForColumn:@"url"]);
}
[rs close];
[db close];

produced this output:

2011-03-06 12:38:59.831 test[93163:207] google'