Fix LP BUG#715738

Analysis:
A query with implicit grouping is one with aggregate functions and
no GROUP BY clause. MariaDB inherits from MySQL an SQL extenstion
that allows mixing aggregate functions with non-aggregate fields.
If a query with such mixed select clause produces an empty result
set, the meaning of aggregate functions is well defined - either
NULL (MIN, MAX, etc.), or 0 (count(*)). However the non-aggregated
fields must also have some value, and the only reasonable value in
the case of empty result is NULL.

The cause of the many wrong results was that if a field is declared
as non-nullable (e.g. because it is a PK or NOT NULL), the semantic
analysis and the optimization phases treat this field as non-nullable,
and generate all related query plan elements based on this assumption.

Later during execution, these incorrectly configured/generated query
plan elements result in a wrong result because the selected fields
are not null due to the not-null assumption during optimization.

Solution:
Detect before the context analysys phase that a query uses implicit
grouping with mixed aggregates/non-aggregates, and set all fields
as nullable. The parser already walks the SELECT clause, and
already sets Item::with_sum_func for Items that reference aggreagate
functions. The patch adds a symmetric Item::with_field so that all
Items that reference an Item_field are marked during their
construction at parse time in the same way as with aggregate function
use.

1 files changed, 8 insertions, 0 deletions

diff --git a/sql/item_func.h b/sql/item_func.h
index 36f089de529..5c5ea33f247 100644
--- a/sql/item_func.h
+++ b/sql/item_func.h
@@ -64,6 +64,7 @@ public:
     allowed_arg_cols(1), arg_count(0)
   {
     with_sum_func= 0;
+    with_field= 0;
   }
   Item_func(Item *a):
     allowed_arg_cols(1), arg_count(1)
@@ -71,6 +72,7 @@ public:
     args= tmp_arg;
     args[0]= a;
     with_sum_func= a->with_sum_func;
+    with_field= a->with_field;
   }
   Item_func(Item *a,Item *b):
     allowed_arg_cols(1), arg_count(2)
@@ -78,6 +80,7 @@ public:
     args= tmp_arg;
     args[0]= a; args[1]= b;
     with_sum_func= a->with_sum_func || b->with_sum_func;
+    with_field= a->with_field || b->with_field;
   }
   Item_func(Item *a,Item *b,Item *c):
     allowed_arg_cols(1)
@@ -88,6 +91,7 @@ public:
       arg_count= 3;
       args[0]= a; args[1]= b; args[2]= c;
       with_sum_func= a->with_sum_func || b->with_sum_func || c->with_sum_func;
+      with_field= a->with_field || b->with_field || c->with_field;
     }
   }
   Item_func(Item *a,Item *b,Item *c,Item *d):
@@ -100,6 +104,8 @@ public:
       args[0]= a; args[1]= b; args[2]= c; args[3]= d;
       with_sum_func= a->with_sum_func || b->with_sum_func ||
 	c->with_sum_func || d->with_sum_func;
+      with_field= a->with_field || b->with_field ||
+        c->with_field || d->with_field;
     }
   }
   Item_func(Item *a,Item *b,Item *c,Item *d,Item* e):
@@ -111,6 +117,8 @@ public:
       args[0]= a; args[1]= b; args[2]= c; args[3]= d; args[4]= e;
       with_sum_func= a->with_sum_func || b->with_sum_func ||
 	c->with_sum_func || d->with_sum_func || e->with_sum_func ;
+      with_field= a->with_field || b->with_field ||
+        c->with_field || d->with_field || e->with_field;
     }
   }
   Item_func(List<Item> &list);