Explanation about for

[Ian Kelly]

2012/1/9 Νικόλαος Κούρας <nikos.kouras at gmail.com>:
> if the MySQL query was:
>
> cursor.execute( '''SELECT host, hits, agent, date FROM visitors WHERE pin =
> %s ORDER BY date DESC''', pin )
>
> can you help me imagine how the mysql database cursor that holds the query
> results would look like? I must somehow visualize it in order to understand
> it!

You can think of it as a pointer, traversing over one row of the
result set at a time.  Hopefully this will come out legibly:

-----------------------------------------------
| HOST | HITS | AGENT | DATE |
-----------------------------------------------            -------------
| foo     | 7       | IE6       | 1/1/11 |   <----   | cursor |
-----------------------------------------------            -------------
| bar     | 42     | Firefox  | 2/2/10 |
-----------------------------------------------
| baz    | 4       | Chrome | 3/3/09 |
------------------------------------------------


> Also what happend if the query was:
> cursor.execute( '''SELECT host FROM visitors") ?
>
> the result would have to be something likelike?
>
> -----------------
> |somehost1|
> -----------------
> |somehost2|
> -----------------
> |somehost3|
> -----------------
> .....................
> .....................
> |somehost n|
> -----------------
>
> So what values host, hits, agent, date would have in 'for host, hits, agent,
> date in
>  dataset' ? Every row has one string how can that be split in 4?

Why don't you try it and see what happens?  But to spare you the
suspense, you would get:

ValueError: need more than 1 value to unpack

Because you can't unpack a 1-length tuple into four variables.  The
code assumes that the query is selecting exactly 4 columns.