diff options
Diffstat (limited to 'sql/item.h')
| -rw-r--r-- | sql/item.h | 34 |
1 files changed, 31 insertions, 3 deletions
diff --git a/sql/item.h b/sql/item.h index 497c2c1d840..ddb98b1f545 100644 --- a/sql/item.h +++ b/sql/item.h @@ -878,6 +878,9 @@ public: static CHARSET_INFO *default_charset(); virtual CHARSET_INFO *compare_collation() { return NULL; } + /* Cache of the result of is_expensive(). */ + int8 is_expensive_cache; + virtual bool walk(Item_processor processor, bool walk_subquery, uchar *arg) { return (this->*processor)(arg); @@ -1081,6 +1084,29 @@ public: */ virtual bool result_as_longlong() { return FALSE; } bool is_datetime(); + + /* + Test whether an expression is expensive to compute. Used during + optimization to avoid computing expensive expressions during this + phase. Also used to force temp tables when sorting on expensive + functions. + TODO: + Normally we should have a method: + cost Item::execution_cost(), + where 'cost' is either 'double' or some structure of various cost + parameters. + + NOTE + This function is now used to prevent evaluation of materialized IN + subquery predicates before it is allowed. grep for + DontEvaluateMaterializedSubqueryTooEarly to see the uses. + */ + virtual bool is_expensive() + { + if (is_expensive_cache < 0) + is_expensive_cache= walk(&Item::is_expensive_processor, 0, (uchar*)0); + return test(is_expensive_cache); + } virtual Field::geometry_type get_geometry_type() const { return Field::GEOM_GEOMETRY; }; String *check_well_formed_result(String *str, bool send_error= 0); @@ -2842,9 +2868,10 @@ class Cached_item_field :public Cached_item uint length; public: - Cached_item_field(Item_field *item) + Cached_item_field(Field *arg_field) : field(arg_field) { - field= item->field; + field= arg_field; + /* TODO: take the memory allocation below out of the constructor. */ buff= (uchar*) sql_calloc(length=field->pack_length()); } bool cmp(void); @@ -3271,7 +3298,8 @@ void mark_select_range_as_dependent(THD *thd, Field *found_field, Item *found_item, Item_ident *resolved_item); -extern Cached_item *new_Cached_item(THD *thd, Item *item); +extern Cached_item *new_Cached_item(THD *thd, Item *item, + bool use_result_field); extern Item_result item_cmp_type(Item_result a,Item_result b); extern void resolve_const_item(THD *thd, Item **ref, Item *cmp_item); extern int stored_field_cmp_to_item(Field *field, Item *item); |