Bug#21904 (parser problem when using IN with a double "(())")

Before this fix, a IN predicate of the form: "IN (( subselect ))", with two
parenthesis, would be evaluated as a single row subselect: if the subselect
returns more that 1 row, the statement would fail.

The SQL:2003 standard defines a special exception in the specification,
and mandates that this particular form of IN predicate shall be equivalent
to "IN ( subselect )", which involves a table subquery and works with more
than 1 row.

This fix implements "IN (( subselect ))", "IN ((( subselect )))" etc
as per the SQL:2003 requirement.

All the details related to the implementation of this change have been
commented in the code, and the relevant sections of the SQL:2003 spec
are given for reference, so they are not repeated here.

Having access to the spec is a requirement to review in depth this patch.

1 files changed, 16 insertions, 0 deletions

diff --git a/sql/item_subselect.h b/sql/item_subselect.h
index f1be99353cc..c866cafd8c0 100644
--- a/sql/item_subselect.h
+++ b/sql/item_subselect.h
@@ -126,6 +126,12 @@ public:
   virtual void reset_value_registration() {}
   enum_parsing_place place() { return parsing_place; }
 
+  /**
+    Get the SELECT_LEX structure associated with this Item.
+    @return the SELECT_LEX structure associated with this Item
+  */
+  st_select_lex* get_select_lex();
+
   friend class select_subselect;
   friend class Item_in_optimizer;
   friend bool Item_field::fix_fields(THD *, Item **);
@@ -169,6 +175,16 @@ public:
   bool null_inside();
   void bring_value();
 
+  /**
+    This method is used to implement a special case of semantic tree
+    rewriting, mandated by a SQL:2003 exception in the specification.
+    The only caller of this method is handle_sql2003_note184_exception(),
+    see the code there for more details.
+    Do not call this method for other purposes.
+    @return the SELECT_LEX structure that was given in the constructor.
+  */
+  st_select_lex* invalidate_and_restore_select_lex();
+
   friend class select_singlerow_subselect;
 };