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MDEV-37713/MDEV-37714 Fold boolean literals in SELECT-list #4754

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MDEV-37713/MDEV-37714 Fold boolean literals in SELECT-list #4754

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39 changes: 39 additions & 0 deletions sql/item_cmpfunc.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -5736,6 +5736,45 @@ bool Item_cond::excl_dep_on_grouping_fields(st_select_lex *sel)
return true;
}

Item *Item_cond::simplify_cond(THD *thd)
{
List_iterator<Item> li(list);
Item *child;
while ((child= li++))
{
if (child->type() == Item::COND_ITEM)
{
Item *new_child= static_cast<Item_cond *>(child)->simplify_cond(thd);
if (new_child != child)
li.replace(new_child);
}
}
bool is_and= functype() == Item_func::COND_AND_FUNC;
bool is_or= functype() == Item_func::COND_OR_FUNC;
if (is_and || is_or)
{
List_iterator<Item> li2(list);
while ((child= li2++))
{
Item *real= child->real_item();
if (real->is_bool_literal())
{
bool v= real->val_bool();
if (is_and && v)
li2.remove();
if (is_and && !v)
return new (thd->mem_root) Item_bool(thd, false);
if (is_or && v)
return new (thd->mem_root) Item_bool(thd, true);
if (is_or && !v)
li2.remove();
}
}
if (list.is_empty())
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@gkodinov gkodinov Mar 9, 2026

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Can the list ever be empty, given that you're removing one of the branches only if another branch exists?

I'd say no. And then this is dead code. And should be turned into an assert.

return new (thd->mem_root) Item_bool(thd, false);
}
return this;
}

void Item_cond_and::mark_as_condition_AND_part(TABLE_LIST *embedding)
{
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1 change: 1 addition & 0 deletions sql/item_cmpfunc.h
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Expand Up @@ -3450,6 +3450,7 @@ class Item_cond :public Item_bool_func
Item *deep_copy(THD *thd) const override;
bool excl_dep_on_table(table_map tab_map) override;
bool excl_dep_on_grouping_fields(st_select_lex *sel) override;
Item *simplify_cond(THD *thd);

private:
void merge_sub_condition(List_iterator<Item>& li);
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17 changes: 17 additions & 0 deletions sql/sql_base.cc
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Expand Up @@ -8223,6 +8223,23 @@ bool setup_fields(THD *thd, Ref_ptr_array ref_pointer_array,
DBUG_RETURN(TRUE); /* purecov: inspected */
}
item= *(it.ref()); // Item might have changed in fix_fields()
/*
If item is a SELECT-list COND_ITEM, rewrite it on the first time this
query is optimized to fold boolean expressions
*/
if (thd->lex->current_select->context_analysis_place == SELECT_LIST &&
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@gkodinov gkodinov Mar 9, 2026

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Any specific reason why you're doing this only for the SELECT list expressions?
Why not do this during fix_fields for all Item_conds for example?

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@gkodinov gkodinov Mar 9, 2026

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Forgot to mention one thing: When doing the optimization you are doing you need to check for NULL-ness!

SELECT true AND NULL FROM t1

should return NULL and not true.

item->type() == Item::COND_ITEM &&
thd->lex->current_select->first_cond_optimization)
{
Query_arena_stmt on_stmt_arena(thd);
Item *new_item= static_cast<Item_cond *>(item)->simplify_cond(thd);
if (new_item != item)
{
new_item->share_name_with(item);
it.replace(new_item);
item= new_item;
}
}
if (!ref.is_null())
{
ref[0]= item;
Expand Down