Subquery cache (MWL#66) added.

libmysqld/Makefile.am:
  The new file added.
mysql-test/r/index_merge_myisam.result:
  subquery_cache optimization option added.
mysql-test/r/myisam_mrr.result:
  subquery_cache optimization option added.
mysql-test/r/subquery_cache.result:
  The subquery cache tests added.
mysql-test/r/subselect3.result:
  Subquery cache switched off to avoid changing read statistics.
mysql-test/r/subselect3_jcl6.result:
  Subquery cache switched off to avoid changing read statistics.
mysql-test/r/subselect_no_mat.result:
  subquery_cache optimization option added.
mysql-test/r/subselect_no_opts.result:
  subquery_cache optimization option added.
mysql-test/r/subselect_no_semijoin.result:
  subquery_cache optimization option added.
mysql-test/r/subselect_sj.result:
  subquery_cache optimization option added.
mysql-test/r/subselect_sj_jcl6.result:
  subquery_cache optimization option added.
mysql-test/t/subquery_cache.test:
  The subquery cache tests added.
mysql-test/t/subselect3.test:
  Subquery cache switched off to avoid changing read statistics.
sql/CMakeLists.txt:
  The new file added.
sql/Makefile.am:
  The new files added.
sql/item.cc:
  Expression cache item (Item_cache_wrapper) added.
  Item_ref and Item_field fixed for correct usage of result field and fast resolwing in SP.
sql/item.h:
  Expression cache item (Item_cache_wrapper) added.
  Item_ref and Item_field fixed for correct usage of result field and fast resolwing in SP.
sql/item_cmpfunc.cc:
  Subquery cache added.
sql/item_cmpfunc.h:
  Subquery cache added.
sql/item_subselect.cc:
  Subquery cache added.
sql/item_subselect.h:
  Subquery cache added.
sql/item_sum.cc:
  Registration of subquery parameters added.
sql/mysql_priv.h:
  subquery_cache optimization option added.
sql/mysqld.cc:
  subquery_cache optimization option added.
sql/opt_range.cc:
  Fix due to subquery cache.
sql/opt_subselect.cc:
  Parameters of the function cahnged.
sql/procedure.h:
  .h file guard added.
sql/sql_base.cc:
  Registration of subquery parameters added.
sql/sql_class.cc:
  Option to allow add indeces to temporary table.
sql/sql_class.h:
  Item iterators added.
  Option to allow add indeces to temporary table.
sql/sql_expression_cache.cc:
  Expression cache for caching subqueries added.
sql/sql_expression_cache.h:
  Expression cache for caching subqueries added.
sql/sql_lex.cc:
  Registration of subquery parameters added.
sql/sql_lex.h:
  Registration of subqueries and subquery parameters added.
sql/sql_select.cc:
  Subquery cache added.
sql/sql_select.h:
  Subquery cache added.
sql/sql_union.cc:
  A new parameter to the function added.
sql/sql_update.cc:
  A new parameter to the function added.
sql/table.cc:
  Procedures to manage temporarty tables index added.
sql/table.h:
  Procedures to manage temporarty tables index added.
storage/maria/ha_maria.cc:
  Fix of handler to allow destoy a table in case of error during the table creation.
storage/maria/ha_maria.h:
  .h file guard added.
storage/myisam/ha_myisam.cc:
  Fix of handler to allow destoy a table in case of error during the table creation.

sql/sql_expression_cache.h

@@ -0,0 +1,80 @@
+#ifndef SQL_EXPRESSION_CACHE_INCLUDED
+#define SQL_EXPRESSION_CACHE_INCLUDED
+
+#include "sql_select.h"
+
+/**
+  Interface for expression cache
+
+  @note
+  Parameters of an expression cache interface are set on the creation of the
+  cache. They are passed when a cache object of the implementation class is
+  constructed. That's why they are not visible in this interface.
+*/
+
+extern ulonglong subquery_cache_miss, subquery_cache_hit;
+
+class Expression_cache :public Sql_alloc
+{
+public:
+  enum result {ERROR, HIT, MISS};
+
+  Expression_cache(){};
+  virtual ~Expression_cache() {};
+  /**
+    Shall check the presence of expression value in the cache for a given
+    set of values of the expression parameters.  Return the result of the
+    expression if it's found in the cache.
+  */
+  virtual result check_value(Item **value)= 0;
+  /**
+    Shall put the value of an expression for given set of its parameters
+    into the expression cache
+  */
+  virtual my_bool put_value(Item *value)= 0;
+};
+
+struct st_table_ref;
+struct st_join_table;
+class Item_field;
+
+
+/**
+  Implementation of expression cache over a temporary table
+*/
+
+class Expression_cache_tmptable :public Expression_cache
+{
+public:
+  Expression_cache_tmptable(THD *thd, List<Item*> &dependants, Item *value);
+  virtual ~Expression_cache_tmptable();
+  virtual result check_value(Item **value);
+  virtual my_bool put_value(Item *value);
+
+private:
+  void init();
+  bool make_equalities();
+
+  /* tmp table parameters */
+  TMP_TABLE_PARAM cache_table_param;
+  /* temporary table to store this cache */
+  TABLE *cache_table;
+  /* Thread handle for the temporary table */
+  THD *table_thd;
+  /* TABLE_REF for index lookup */
+  struct st_table_ref ref;
+  /* Cached result */
+  Item_field *cached_result;
+  /* List of references to the parameters of the expression */
+  List<Item*> *list;
+  /* List of items */
+  List<Item> items;
+  /* Value Item example */
+  Item *val;
+  /* Expression to check after index lookup */
+  Item *equalities;
+  /* Set on if the object has been succesfully initialized with init() */
+  bool inited;
+};
+
+#endif /* SQL_EXPRESSION_CACHE_INCLUDED */