Hi Alexander!

I was looking through this patch as I am rather familiar with this code. I didn't take time to test this out, but maybe you can explain if this is a possible concern or not:

index 4a95189..7d1532c 100644

--- a/sql/item_sum.cc

+++ b/sql/item_sum.cc

@@ -404,7 +404,7 @@ bool Item_sum::register_sum_func(THD *thd, Item **ref)

for (sl= thd->lex->current_select;

sl && sl != aggr_sel && sl->master_unit()->item;

sl= sl->master_unit()->outer_select() )

- sl->master_unit()->item->with_sum_func= 1;

+ sl->master_unit()->item->get_with_sum_func_cache()->set_with_sum_func();

}

thd->lex->current_select->mark_as_dependent(thd, aggr_sel, NULL);

@@ -484,7 +484,6 @@ void Item_sum::mark_as_sum_func()

cur_select->n_sum_items++;

cur_select->with_sum_func= 1;

const_item_cache= false;

- with_sum_func= 1;

with_field= 0;

window_func_sum_expr_flag= false;

}

diff --git a/sql/item_sum.h b/sql/item_sum.h

index 96f1153..37f3fe0 100644

--- a/sql/item_sum.h

+++ b/sql/item_sum.h

@@ -582,6 +582,8 @@ class Item_sum :public Item_func_or_sum

void mark_as_window_func_sum_expr() { window_func_sum_expr_flag= true; }

bool is_window_func_sum_expr() { return window_func_sum_expr_flag; }

virtual void setup_caches(THD *thd) {};

+ bool with_sum_func() const { return true; }

};

For Item_sum::register_sum_func, if sl->master_unit()->item is an Item_sum_sum for example, an Item_sum won't have get_with_sum_func_cache() overwritten so it will be the base Item::get_with_sum_func_cache(), which returns null and you will crash. Am I missing something?

Is it impossible for sl->master_unit()->item to be an Item_sum_... subclass?

I am not a very big fan of the get_with_sum_func_cache() indirection required and would prefer, if possible to call set_with_sum_func() directly. Perhaps behind the scenes the set function can do that and throw an assert if the call is illegal? (Just an opinion, not something I have a very very strong opinion on.

Also, I have a feeling that it's sufficient to keep just join_with_sum_func. I can't really think of a place where that was not the intent anyway, but those few cases where copy_with_sum_func is used need to be analysed throughly to make sure.

Regards,

Vicențiu

PS: Yes, the review assigned to me is coming :)

On Tue, 29 May 2018 at 15:07 Alexander Barkov <bar@mariadb.com> wrote:

Hello Sanja,

I recently worked on MDEV-16309 and had hard time to find
which Item classes in the hierarchy:
- have always with_sum_func==true
- have always with_sum_func==false
- have variable with_sum_func

To make it sure, before actually working on MDEV-16309,
I had to create a separate working tree and did with
Item::with_sum_func the same change that we previously
did for Item::with_subselect in:

MDEV-14517 Cleanup for Item::with_subselect and Item::has_subquery()
(which you reviewed)

- I find the code easier to read this way
(instead of searching for all possible assignments,
one can search who overrides the method)
- Also, some Item can become smaller in size.

It's pity to throw the patch away. So perhaps we could just apply it.

Can you please have a look?

Thanks.

I the meanwhile I'll create a new MDEV for it
(with a similar description to MDEV-14517)
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