Iphone 从xcode无法为sqlite执行DISTINCT关键字

-void readProductsFromDatabase{ //设置数据库对象 sqlite3*数据库

// Init the animals Array
products = [[NSMutableArray alloc] init];

// Open the database from the users filessytem
if(sqlite3_open([databasePath UTF8String], &database) == SQLITE_OK) {
    NSLog(@"db opened");
    // Setup the SQL Statement and compile it for faster access
    const char *sqlStatement = "SELECT DISTINCT productname FROM iphone ";
            sqlite3_stmt *compiledStatement;
    if(sqlite3_prepare_v2(database, sqlStatement, -1, &compiledStatement, NULL) == SQLITE_OK) 
    {
        // Loop through the results and add them to the feeds array
        while(sqlite3_step(compiledStatement) == SQLITE_ROW)
        {
            NSLog(@"inside sqlite3 prepare");
            // Read the data from the result row
            NSString *aName = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 2)];


                    }
    }
    // Release the compiled statement from memory
    sqlite3_finalize(compiledStatement);

}
sqlite3_close(database);

}

我的问题是

const char*sqlStatement=从iphone中选择不同的产品名称

这行没有执行，我使用的是sqlite3， 提前感谢，

问题就在这一步 NSString*aName=[NSString stringWithUTF8String:char*sqlite3_column_textcompiledStatement，2]

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用0代替2，这行不执行是什么意思？