Manual merge from mysql-trunk-merge.

sql/sql_select.h

@@ -61,6 +61,8 @@ class store_key;
 typedef struct st_table_ref
 {
   bool		key_err;
+  /** True if something was read into buffer in join_read_key.  */
+  bool          has_record;
   uint          key_parts;                ///< num of ...
   uint          key_length;               ///< length of key_buff
   int           key;                      ///< key no
@@ -88,6 +90,11 @@ typedef struct st_table_ref
   table_map	depend_map;		  ///< Table depends on these tables.
   /* null byte position in the key_buf. Used for REF_OR_NULL optimization */
   uchar          *null_ref_key;
+  /*
+    The number of times the record associated with this key was used
+    in the join.
+  */
+  ha_rows       use_count;
 } TABLE_REF;