I want to alter a table if that column already exists. If it doesn't I want to add it.

My code :

```
-(void) alterDB{
    sqlite3_stmt *statement; 
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString *databasePath = [documentsDirectory stringByAppendingPathComponent:DATABASE_NAME];

    if(sqlite3_open([databasePath UTF8String], &database) == SQLITE_OK)
    {

        NSString *updateSQL = [NSString stringWithFormat: @"ALTER TABLE diagramInfo ADD COLUMN testColumn VARCHAR"];
        const char *update_stmt = [updateSQL UTF8String];
        sqlite3_prepare_v2(database, update_stmt, -1, &statement, NULL);

        if(sqlite3_step(statement)==SQLITE_DONE) 
        {
            UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"DB altered" message:@"Success" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];    
            [alert show];
            [alert release];
            alert=nil;

        }
        else 
        {
            UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"DB Updation" message:@"DB not Altered" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];   
            [alert show];
            [alert release];
            alert=nil;
        }   
        // Release the compiled statement from memory
        sqlite3_finalize(statement);    
        sqlite3_close(database);
    }
}

```