MWL#17: Table elimination

- Last fixes

sql/item.cc:
  MWL#17: Table elimination
  - Don't make multiple calls of ::walk(check_column_usage_processor),
    call once and cache the value
sql/item.h:
  MWL#17: Table elimination
  - s/KEYUSE::usable/KEYUSE::type/, more comments
sql/opt_table_elimination.cc:
  MWL#17: Table elimination
  - Don't make multiple calls of ::walk(check_column_usage_processor),
    call once and cache the value
sql/sql_select.cc:
  MWL#17: Table elimination
  - s/KEYUSE::usable/KEYUSE::type/, more comments
sql/sql_select.h:
  MWL#17: Table elimination
  - s/KEYUSE::usable/KEYUSE::type/, more comments
sql/table.h:
  MWL#17: Table elimination
  - Better comments

1 files changed, 8 insertions, 5 deletions

diff --git a/sql/item.h b/sql/item.h
index 6f0bf02bdae..0e74c742d99 100644
--- a/sql/item.h
+++ b/sql/item.h
@@ -1018,11 +1018,14 @@ public:
 };
 
 /* Data for Item::check_column_usage_processor */
-typedef struct  
-{
-  table_map allowed_tables;
-  TABLE *table;
-  uint keyno;
+typedef struct 
+{
+  TABLE *table;         /* Table of interest */
+  uint keyno;           /* Index of interest */
+  uint forbidden_part;  /* key part which one is not allowed to refer to */
+  /* [Set by processor] used tables, besides the table of interest */
+  table_map used_tables; 
+  /* [Set by processor] Parts of index of interest that expression refers to */
   uint needed_key_parts;
 } Field_processor_info;