Hi!
On Jul 12, will@stripped wrote:
> I accidentally hit send (dur), so here's the rest of the doc:
>
> Each COND is a tree of conditions. The top level COND is actually an
> Item_cond (see item_cmpfunc.h for more the class definition).
I don't think it's always an Item_cond, more likely it depends on your
query. If you have WHERE a=5, for example, without AND/OR, there's no
Item_cond in here, and unless MySQL internally creates a dummy Item_cond
(which I don't think it does), top level COND will be Item_func_eq.
> To walk
> through the tree, you have to use the function:
> void traverse_cond(Cond_traverser, void *arg, traverse_order order);
> The traverse order can be postfix or prefix. MySQL cluster uses prefix
> order which means that "WHERE row1 = 'blah' and row2 = 3" would be
> ordered like this:
> Item_cond_and -> Item_func_eq -> Item_field -> Item_int -> Item_func_eq
> -> Item_field -> Item_string -> NULL;
> [ed: how do i know how many arguments each item has?]
Base Item doesn't have arguments, Item_func does, use
Item_func::argument_count()
> For more advanced condition pushdown, take a look at
> void ndb_serialize_cond(const Item *item, void *arg)
> in ha_ndbcluster_cond.cc
>
Regards / Mit vielen Grüssen,
Sergei
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