WL#2985 "Partition Pruning"

mysql-test/t/partition_pruning.test

+#
+# Partition pruning tests. Currently we only detect which partitions to
+# prune, so the test is EXPLAINs.
+#
+-- source include/have_partition.inc
+
+--disable_warnings
+drop table if exists t1,t2,t3,t4,t5,t6,t7,t8,t9;
+--enable_warnings
+
+
+# Check if we can infer from condition on partition fields that 
+# no records will match.
+create table t1 ( a int not null) partition by hash(a) partitions 2;
+insert into t1 values (1),(2),(3);
+explain select * from t1 where a=5 and a=6;
+drop table t1;
+
+# Simple HASH partitioning
+create table t1 (
+  a int(11) not null
+) partition by hash (a) partitions 2;
+insert into t1 values (1),(2),(3);
+
+explain partitions select * from t1 where a=1;
+explain partitions select * from t1 where a=2;
+explain partitions select * from t1 where a=1 or a=2;
+
+# Partitioning over several fields
+create table t2 (
+  a int not null,
+  b int not null
+) partition by key(a,b) partitions 2;
+insert into t2 values (1,1),(2,2),(3,3);
+
+explain partitions select * from t2 where a=1;
+explain partitions select * from t2 where b=1;
+
+explain partitions select * from t2 where a=1 and b=1;
+
+# RANGE(expr) partitioning 
+create table t3 (
+  a int
+)
+partition by range (a*1) ( 
+  partition p0 values less than (10),
+  partition p1 values less than (20)
+);
+insert into t3 values (5),(15);
+
+explain partitions select * from t3 where a=11;
+explain partitions select * from t3 where a=10;
+explain partitions select * from t3 where a=20;
+
+explain partitions select * from t3 where a=30;
+
+# LIST(expr) partitioning
+create table t4 (a int not null, b int not null) partition by LIST (a+b) (
+  partition p0 values in (12),
+  partition p1 values in (14)
+);
+insert into t4 values (10,2), (10,4);
+
+# empty OR one
+explain partitions select * from t4 where (a=10 and b=1) or (a=10 and b=2);
+
+# empty OR one OR empty
+explain partitions select * from t4 
+  where (a=10 and b=1) or (a=10 and b=2) or (a=10 and b = 3);
+
+# one OR empty OR one
+explain partitions select * from t4 where (a=10 and b=2) or (a=10 and b=3)
+  or (a=10 and b = 4);
+
+# empty OR full
+explain partitions select * from t4 where (a=10 and b=1) or a=11;
+
+# one OR full
+explain partitions select * from t4 where (a=10 and b=2) or a=11;
+
+drop table t1, t2, t3, t4;
+
+# LIST(expr)/HASH subpartitioning.
+create table t5 (a int not null, b int not null, 
+                 c int not null, d int not null) 
+partition by LIST(a+b) subpartition by HASH (c+d) subpartitions 2
+(
+  partition p0 values in (12),
+  partition p1 values in (14)
+);
+ 
+insert into t5 values (10,2,0,0), (10,4,0,0), (10,2,0,1), (10,4,0,1);
+explain partitions select * from t5;
+
+# empty OR one OR empty
+explain partitions select * from t5
+  where (a=10 and b=1) or (a=10 and b=2) or (a=10 and b = 3);
+
+# one OR empty OR one
+explain partitions select * from t5 where (a=10 and b=2) or (a=10 and b=3)
+  or (a=10 and b = 4);
+
+# conditions on subpartitions only
+explain partitions select * from t5 where (c=1 and d=1);
+explain partitions select * from t5 where (c=2 and d=1);
+
+# mixed partition/subpartitions.
+explain partitions select * from t5 where (a=10 and b=2 and c=1 and d=1) or 
+(c=2 and d=1);
+
+# same as above
+explain partitions select * from t5 where (a=10 and b=2 and c=1 and d=1) or 
+(b=2 and c=2 and d=1);
+
+# LIST(field) partitioning, interval analysis.
+create table t6 (a int not null) partition by LIST(a) (
+  partition p1 values in (1),
+  partition p3 values in (3),
+  partition p5 values in (5),
+  partition p7 values in (7),
+  partition p9 values in (9)
+);
+insert into t6 values (1),(3),(5);
+
+explain partitions select * from t6 where a <  1;
+explain partitions select * from t6 where a <= 1;
+explain partitions select * from t6 where a >  9;
+explain partitions select * from t6 where a >= 9;
+
+explain partitions select * from t6 where a > 0 and a < 5;
+explain partitions select * from t6 where a > 5 and a < 12;
+explain partitions select * from t6 where a > 3 and a < 8 ;
+
+explain partitions select * from t6 where a >= 0 and a <= 5;
+explain partitions select * from t6 where a >= 5 and a <= 12;
+explain partitions select * from t6 where a >= 3 and a <= 8;
+
+explain partitions select * from t6 where a > 3 and a < 5;
+
+# RANGE(field) partitioning, interval analysis.
+create table t7 (a int not null) partition by RANGE(a) (
+  partition p10 values less than (10),
+  partition p30 values less than (30),
+  partition p50 values less than (50),
+  partition p70 values less than (70),
+  partition p90 values less than (90)
+);
+insert into t7 values (10),(30),(50);
+
+# leftmost intervals
+explain partitions select * from t7 where a < 5;
+explain partitions select * from t7 where a < 10;
+explain partitions select * from t7 where a <= 10;
+explain partitions select * from t7 where a = 10;
+
+#rightmost intervals
+explain partitions select * from t7 where a < 90;
+explain partitions select * from t7 where a = 90;
+explain partitions select * from t7 where a > 90;
+explain partitions select * from t7 where a >= 90;
+
+# misc intervals
+explain partitions select * from t7 where a > 11 and a < 29;
+
+# LIST(monontonic_func) partitioning
+create table t8 (a date not null) partition by RANGE(YEAR(a)) (
+  partition p0 values less than (1980),
+  partition p1 values less than (1990),
+  partition p2 values less than (2000)
+);
+insert into t8 values ('1985-05-05'),('1995-05-05');
+
+explain partitions select * from t8 where a < '1980-02-02';
+
+# LIST(strict_monotonic_func) partitioning
+create table t9 (a date not null) partition by RANGE(TO_DAYS(a)) (
+  partition p0 values less than (732299), -- 2004-12-19
+  partition p1 values less than (732468), -- 2005-06-06
+  partition p2 values less than (732664)  -- 2005-12-19
+);
+insert into t9 values ('2005-05-05'), ('2005-04-04');
+
+explain partitions select * from t9 where a <  '2004-12-19';
+explain partitions select * from t9 where a <= '2004-12-19';
+
+drop table t5,t6,t7,t8,t9;
+
+# Test the case where we can't create partitioning 'index'
+create table t1 (a enum('a','b','c','d') default 'a') 
+  partition by hash (ascii(a)) partitions 2;
+insert into t1 values ('a'),('b'),('c');
+explain partitions select * from t1 where a='b';
+drop table t1;
+
+

sql/ha_ndbcluster.cc

@@ -3123,7 +3123,6 @@ void ha_ndbcluster::info(uint flag)
   DBUG_VOID_RETURN;
 }
 
-
 int ha_ndbcluster::extra(enum ha_extra_function operation)
 {
   DBUG_ENTER("extra");
@@ -3132,6 +3131,8 @@ int ha_ndbcluster::extra(enum ha_extra_function operation)
     DBUG_PRINT("info", ("HA_EXTRA_RESET"));
     DBUG_PRINT("info", ("Clearing condition stack"));
     cond_clear();
+    if (m_part_info)
+      bitmap_clear_all(&m_part_info->used_partitions);
     break;
   case HA_EXTRA_IGNORE_DUP_KEY:       /* Dup keys don't rollback everything*/
     DBUG_PRINT("info", ("HA_EXTRA_IGNORE_DUP_KEY"));

sql/ha_partition.cc

@@ -2795,6 +2795,8 @@ int ha_partition::reset(void)
   handler **file;
   DBUG_ENTER("ha_partition::reset");
   file= m_file;
+  if (m_part_info)
+    bitmap_clear_all(&m_part_info->used_partitions);
   do
   {
     if ((tmp= (*file)->reset()))

sql/handler.h

@@ -535,12 +535,34 @@ class partition_info :public Sql_alloc {
   List<char> part_field_list;
   List<char> subpart_field_list;
   
+  /* 
+    If there is no subpartitioning, use only this func to get partition ids.
+    If there is subpartitioning, use the this func to get partition id when
+    you have both partition and subpartition fields.
+  */
   get_part_id_func get_partition_id;
+
+  /* Get partition id when we don't have subpartition fields */
   get_part_id_func get_part_partition_id;
+
+  /* 
+    Get subpartition id when we have don't have partition fields by we do
+    have subpartition ids.
+    Mikael said that for given constant tuple 
+    {subpart_field1, ..., subpart_fieldN} the subpartition id will be the
+    same in all subpartitions
+  */
   get_subpart_id_func get_subpartition_id;
   
+  /* NULL-terminated list of fields used in partitioned expression */
   Field **part_field_array;
+  /* NULL-terminated list of fields used in subpartitioned expression */
   Field **subpart_field_array;
+
+  /* 
+    Array of all fields used in partition and subpartition expression,
+    without duplicates, NULL-terminated.
+  */
   Field **full_part_field_array;
 
   Item *part_expr;
@@ -548,6 +570,17 @@ class partition_info :public Sql_alloc {
 
   Item *item_free_list;
   
+  /* 
+    A bitmap of partitions used by the current query. 
+    Usage pattern:
+    * It is guaranteed that all partitions are set to be unused on query start.
+    * Before index/rnd_init(), partition pruning code sets the bits for used
+      partitions.
+    * The handler->extra(HA_EXTRA_RESET) call at query end sets all partitions
+      to be unused.
+  */
+  MY_BITMAP used_partitions;
+
   union {
     longlong *range_int_array;
     LIST_PART_ENTRY *list_array;
@@ -747,6 +780,13 @@ void get_full_part_id_from_key(const TABLE *table, byte *buf,
 bool mysql_unpack_partition(THD *thd, const uchar *part_buf,
                             uint part_info_len, TABLE *table,
                             enum db_type default_db_type);
+void make_used_partitions_str(partition_info *part_info, String *parts_str);
+uint32 get_list_array_idx_for_endpoint(partition_info *part_info,
+                                       bool left_endpoint,
+                                       bool include_endpoint);
+uint32 get_partition_id_range_for_endpoint(partition_info *part_info,
+                                           bool left_endpoint,
+                                           bool include_endpoint);
 #endif
 
 

sql/item.h

@@ -368,6 +368,28 @@ class Name_resolution_context_state
   }
 };
 
+
+/*
+  This enum is used to report information about monotonicity of function
+  represented by Item* tree.
+  Monotonicity is defined only for Item* trees that represent table
+  partitioning expressions (i.e. have no subselects/user vars/PS parameters
+  etc etc). An Item* tree is assumed to have the same monotonicity properties
+  as its correspoinding function F:
+
+  [signed] longlong F(field1, field2, ...) {
+    put values of field_i into table record buffer;
+    return item->val_int(); 
+  }
+*/
+
+typedef enum monotonicity_info 
+{
+   NON_MONOTONIC,              /* none of the below holds */
+   MONOTONIC_INCREASING,       /* F() is unary and "x < y" => "F(x) <  F(y)" */
+   MONOTONIC_STRICT_INCREASING /* F() is unary and "x < y" => "F(x) <= F(y)" */
+} enum_monotonicity_info;
+
 /*************************************************************************/
 
 typedef bool (Item::*Item_processor)(byte *arg);
@@ -465,6 +487,15 @@ class Item {
   virtual Item_result cast_to_int_type() const { return result_type(); }
   virtual enum_field_types field_type() const;
   virtual enum Type type() const =0;
+  
+  /*
+    Return information about function monotonicity. See comment for
+    enum_monotonicity_info for details. This function can only be called
+    after fix_fields() call.
+  */
+  virtual enum_monotonicity_info get_monotonicity_info() const
+  { return NON_MONOTONIC; }
+
   /* valXXX methods must return NULL or 0 or 0.0 if null_value is set. */
   /*
     Return double precision floating point representation of item.
@@ -1138,6 +1169,10 @@ class Item_field :public Item_ident
   {
     return field->type();
   }
+  enum_monotonicity_info get_monotonicity_info() const
+  {
+    return MONOTONIC_STRICT_INCREASING;
+  }
   Field *get_tmp_table_field() { return result_field; }
   Field *tmp_table_field(TABLE *t_arg) { return result_field; }
   bool get_date(TIME *ltime,uint fuzzydate);

sql/item_timefunc.cc

@@ -885,6 +885,19 @@ longlong Item_func_to_days::val_int()
   return (longlong) calc_daynr(ltime.year,ltime.month,ltime.day);
 }
 
+enum_monotonicity_info Item_func_to_days::get_monotonicity_info() const
+{
+  if (args[0]->type() == Item::FIELD_ITEM)
+  {
+    if (args[0]->field_type() == MYSQL_TYPE_DATE)
+      return MONOTONIC_STRICT_INCREASING;
+    if (args[0]->field_type() == MYSQL_TYPE_DATETIME)
+      return MONOTONIC_INCREASING;
+  }
+  return NON_MONOTONIC;
+}
+
+
 longlong Item_func_dayofyear::val_int()
 {
   DBUG_ASSERT(fixed == 1);
@@ -1067,6 +1080,14 @@ longlong Item_func_year::val_int()
   return (longlong) ltime.year;
 }
 
+enum_monotonicity_info Item_func_year::get_monotonicity_info() const
+{
+  if (args[0]->type() == Item::FIELD_ITEM &&
+      (args[0]->field_type() == MYSQL_TYPE_DATE ||
+       args[0]->field_type() == MYSQL_TYPE_DATETIME))
+    return MONOTONIC_INCREASING;
+  return NON_MONOTONIC;
+}
 
 longlong Item_func_unix_timestamp::val_int()
 {

sql/item_timefunc.h

@@ -65,6 +65,7 @@ class Item_func_to_days :public Item_int_func
     max_length=6*MY_CHARSET_BIN_MB_MAXLEN;
     maybe_null=1; 
   }
+  enum_monotonicity_info get_monotonicity_info() const;
 };
 
 
@@ -234,6 +235,7 @@ class Item_func_year :public Item_int_func
   Item_func_year(Item *a) :Item_int_func(a) {}
   longlong val_int();
   const char *func_name() const { return "year"; }
+  enum_monotonicity_info get_monotonicity_info() const;
   void fix_length_and_dec()
   { 
     decimals=0;

sql/opt_range.h

@@ -249,6 +249,7 @@ class QUICK_SELECT_I
 
 
 struct st_qsel_param;
+class PARAM;
 class SEL_ARG;
 
 /*
@@ -283,12 +284,12 @@ class QUICK_RANGE_SELECT : public QUICK_SELECT_I
   QUICK_RANGE_SELECT *get_quick_select_for_ref(THD *thd, TABLE *table,
                                                struct st_table_ref *ref,
                                                ha_rows records);
-  friend bool get_quick_keys(struct st_qsel_param *param,
+  friend bool get_quick_keys(PARAM *param,
                              QUICK_RANGE_SELECT *quick,KEY_PART *key,
                              SEL_ARG *key_tree,
                              char *min_key, uint min_key_flag,
                              char *max_key, uint max_key_flag);
-  friend QUICK_RANGE_SELECT *get_quick_select(struct st_qsel_param*,uint idx,
+  friend QUICK_RANGE_SELECT *get_quick_select(PARAM*,uint idx,
                                               SEL_ARG *key_tree,
                                               MEM_ROOT *alloc);
   friend class QUICK_SELECT_DESC;
@@ -718,4 +719,8 @@ QUICK_RANGE_SELECT *get_quick_select_for_ref(THD *thd, TABLE *table,
                                              ha_rows records);
 uint get_index_for_order(TABLE *table, ORDER *order, ha_rows limit);
 
+#ifdef WITH_PARTITION_STORAGE_ENGINE
+bool prune_partitions(THD *thd, TABLE *table, Item *pprune_cond);
+#endif
+
 #endif

sql/sql_class.cc

@@ -745,6 +745,13 @@ int THD::send_explain_fields(select_result *result)
   field_list.push_back(new Item_empty_string("select_type", 19, cs));
   field_list.push_back(item= new Item_empty_string("table", NAME_LEN, cs));
   item->maybe_null= 1;
+#ifdef WITH_PARTITION_STORAGE_ENGINE
+  if (lex->describe & DESCRIBE_PARTITIONS)
+  {
+    field_list.push_back(item= new Item_empty_string("partitions", 10, cs));
+    item->maybe_null= 1;
+  }
+#endif
   field_list.push_back(item= new Item_empty_string("type", 10, cs));
   item->maybe_null= 1;
   field_list.push_back(item=new Item_empty_string("possible_keys",

sql/sql_lex.h

@@ -102,6 +102,11 @@ enum enum_sql_command {
 // describe/explain types
 #define DESCRIBE_NORMAL		1
 #define DESCRIBE_EXTENDED	2
+/*
+  This is not #ifdef'ed because we want "EXPLAIN PARTITIONS ..." to produce
+  additional "partitions" column even if partitioning is not compiled in.
+*/
+#define DESCRIBE_PARTITIONS	4
 
 enum enum_sp_suid_behaviour
 {

sql/sql_partition.cc

@@ -2477,16 +2477,94 @@ bool get_partition_id_list(partition_info *part_info,
     if (list_value < part_func_value)
       min_list_index= list_index + 1;
     else if (list_value > part_func_value)
+    {
+      if (!list_index)
+        goto notfound;
       max_list_index= list_index - 1;
-    else {
+    }
+    else
+    {
       *part_id= (uint32)list_array[list_index].partition_id;
       DBUG_RETURN(FALSE);
     }
   }
+notfound:
   *part_id= 0;
   DBUG_RETURN(TRUE);
 }
 
+/*
+  Find the part of part_info->list_array that corresponds to given interval
+  
+  SYNOPSIS 
+    get_list_array_idx_for_endpoint()
+      part_info         Partitioning info (partitioning type must be LIST)
+      left_endpoint     TRUE  - the interval is [a; +inf) or (a; +inf)
+                        FALSE - the interval is (-inf; a] or (-inf; a)
+      include_endpoint  TRUE iff the interval includes the endpoint
+
+  DESCRIPTION
+    This function finds the part of part_info->list_array where values of
+    list_array[idx].list_value are contained within the specifed interval.
+    list_array is ordered by list_value, so
+    1. For [a; +inf) or (a; +inf)-type intervals (left_endpoint==TRUE), the 
+       sought array part starts at some index idx and continues till array 
+       end.
+       The function returns first number idx, such that 
+       list_array[idx].list_value is contained within the passed interval.
+       
+    2. For (-inf; a] or (-inf; a)-type intervals (left_endpoint==FALSE), the
+       sought array part starts at array start and continues till some last 
+       index idx.
+       The function returns first number idx, such that 
+       list_array[idx].list_value is NOT contained within the passed interval.
+       If all array elements are contained, part_info->no_list_values is
+       returned.
+
+  NOTE
+    The caller will call this function and then will run along the part of 
+    list_array to collect partition ids. If the number of list values is 
+    significantly higher then number of partitions, this could be slow and
+    we could invent some other approach. The "run over list array" part is
+    already wrapped in a get_next()-like function.
+
+  RETURN
+    The edge of corresponding part_info->list_array part.
+*/
+
+uint32 get_list_array_idx_for_endpoint(partition_info *part_info,
+                                       bool left_endpoint,
+                                       bool include_endpoint)
+{
+  DBUG_ENTER("get_list_array_idx_for_endpoint");
+  LIST_PART_ENTRY *list_array= part_info->list_array;
+  uint list_index;
+  longlong list_value;
+  uint min_list_index= 0, max_list_index= part_info->no_list_values - 1;
+  longlong part_func_value= part_info->part_expr->val_int();
+  while (max_list_index >= min_list_index)
+  {
+    list_index= (max_list_index + min_list_index) >> 1;
+    list_value= list_array[list_index].list_value;
+    if (list_value < part_func_value)
+      min_list_index= list_index + 1;
+    else if (list_value > part_func_value)
+    {
+      if (!list_index)
+        goto notfound;
+      max_list_index= list_index - 1;
+    }
+    else 
+    {
+      DBUG_RETURN(list_index + test(left_endpoint ^ include_endpoint));
+    }
+  }
+notfound:
+  if (list_value < part_func_value)
+    list_index++;
+  DBUG_RETURN(list_index);
+}
+
 
 bool get_partition_id_range(partition_info *part_info,
                             uint32 *part_id)
@@ -2516,6 +2594,89 @@ bool get_partition_id_range(partition_info *part_info,
   DBUG_RETURN(FALSE);
 }
 
+
+/*
+  Find the part of part_info->range_int_array that covers the given interval
+  
+  SYNOPSIS 
+    get_partition_id_range_for_endpoint()
+      part_info         Partitioning info (partitioning type must be RANGE)
+      left_endpoint     TRUE  - the interval is [a; +inf) or (a; +inf)
+                        FALSE - the interval is (-inf; a] or (-inf; a).
+      include_endpoint  TRUE <=> the endpoint itself is included in the
+                        interval
+
+  DESCRIPTION
+    This function finds the part of part_info->range_int_array where the
+    elements have non-empty intersections with the given interval.
+    
+    A range_int_array element at index idx represents the interval
+      
+      [range_int_array[idx-1], range_int_array[idx]),
+
+    intervals are disjoint and ordered by their right bound, so
+    
+    1. For [a; +inf) or (a; +inf)-type intervals (left_endpoint==TRUE), the
+       sought array part starts at some index idx and continues till array 
+       end.
+       The function returns first number idx, such that the interval
+       represented by range_int_array[idx] has non empty intersection with 
+       the passed interval.
+       
+    2. For (-inf; a] or (-inf; a)-type intervals (left_endpoint==FALSE), the
+       sought array part starts at array start and continues till some last 
+       index idx.
+       The function returns first number idx, such that the interval
+       represented by range_int_array[idx] has EMPTY intersection with the
+       passed interval.
+       If the interval represented by the last array element has non-empty 
+       intersection with the passed interval, part_info->no_parts is
+       returned.
+       
+  RETURN
+    The edge of corresponding part_info->range_int_array part.
+*/
+
+uint32 get_partition_id_range_for_endpoint(partition_info *part_info,
+                                           bool left_endpoint,
+                                           bool include_endpoint)
+{
+  DBUG_ENTER("get_partition_id_range_for_endpoint");
+  longlong *range_array= part_info->range_int_array;
+  uint max_partition= part_info->no_parts - 1;
+  uint min_part_id= 0, max_part_id= max_partition, loc_part_id;
+  longlong part_func_value= part_info->part_expr->val_int();
+  while (max_part_id > min_part_id)
+  {
+    loc_part_id= (max_part_id + min_part_id + 1) >> 1;
+    if (range_array[loc_part_id] < part_func_value)
+      min_part_id= loc_part_id + 1;
+    else
+      max_part_id= loc_part_id - 1;
+  }
+  loc_part_id= max_part_id;
+  if (loc_part_id < max_partition && 
+      part_func_value >= range_array[loc_part_id+1])
+  {
+     loc_part_id++;
+  }
+  if (left_endpoint)
+  {
+    if (part_func_value >= range_array[loc_part_id])
+      loc_part_id++;
+  }
+  else 
+  {
+    if (part_func_value == range_array[loc_part_id])
+      loc_part_id += test(include_endpoint);
+    else if (part_func_value > range_array[loc_part_id])
+      loc_part_id++;
+    loc_part_id++;
+  }
+  DBUG_RETURN(loc_part_id);
+}
+
+
 bool get_partition_id_hash_nosub(partition_info *part_info,
                                  uint32 *part_id)
 {
@@ -3204,10 +3365,16 @@ bool mysql_unpack_partition(THD *thd, const uchar *part_buf,
   */
     uint part_func_len= part_info->part_func_len;
     uint subpart_func_len= part_info->subpart_func_len; 
+    uint bitmap_bits= part_info->no_subparts? 
+                       (part_info->no_subparts* part_info->no_parts):
+                        part_info->no_parts;
+    uint bitmap_bytes= bitmap_buffer_size(bitmap_bits);
+    uint32 *bitmap_buf;
     char *part_func_string, *subpart_func_string= NULL;
     if (!((part_func_string= thd->alloc(part_func_len))) ||
         (subpart_func_len &&
-        !((subpart_func_string= thd->alloc(subpart_func_len)))))
+        !((subpart_func_string= thd->alloc(subpart_func_len)))) ||
+        !((bitmap_buf= (uint32*)thd->alloc(bitmap_bytes))))
     {
       my_error(ER_OUTOFMEMORY, MYF(0), part_func_len);
       free_items(thd->free_list);
@@ -3220,6 +3387,8 @@ bool mysql_unpack_partition(THD *thd, const uchar *part_buf,
              subpart_func_len);
     part_info->part_func_string= part_func_string;
     part_info->subpart_func_string= subpart_func_string;
+
+    bitmap_init(&part_info->used_partitions, bitmap_buf, bitmap_bytes*8, FALSE);
   }
 
   result= FALSE;
@@ -3293,3 +3462,60 @@ void set_key_field_ptr(KEY *key_info, const byte *new_buf,
   } while (++i < key_parts);
   DBUG_VOID_RETURN;
 }
+
+
+/*
+  Fill the string comma-separated line of used partitions names
+  SYNOPSIS
+    make_used_partitions_str()
+      part_info  IN  Partitioning info
+      parts_str  OUT The string to fill
+*/
+
+void make_used_partitions_str(partition_info *part_info, String *parts_str)
+{
+  parts_str->length(0);
+  partition_element *pe;
+  uint partition_id= 0;
+  List_iterator<partition_element> it(part_info->partitions);
+  
+  if (part_info->subpart_type != NOT_A_PARTITION)
+  {
+    partition_element *head_pe;
+    while ((head_pe= it++))
+    {
+      List_iterator<partition_element> it2(head_pe->subpartitions);
+      while ((pe= it2++))
+      {
+        if (bitmap_is_set(&part_info->used_partitions, partition_id))
+        {
+          if (parts_str->length())
+            parts_str->append(',');
+          parts_str->append(head_pe->partition_name,
+                           strlen(head_pe->partition_name),
+                           system_charset_info);
+          parts_str->append('_');
+          parts_str->append(pe->partition_name,
+                           strlen(pe->partition_name),
+                           system_charset_info);
+        }
+        partition_id++;
+      }
+    }
+  }
+  else
+  {
+    while ((pe= it++))
+    {
+      if (bitmap_is_set(&part_info->used_partitions, partition_id))
+      {
+        if (parts_str->length())
+          parts_str->append(',');
+        parts_str->append(pe->partition_name, strlen(pe->partition_name),
+                         system_charset_info);
+      }
+      partition_id++;
+    }
+  }
+}
+

sql/sql_select.cc

@@ -633,6 +633,21 @@ JOIN::optimize()
     DBUG_RETURN(0);
   }
 
+#ifdef WITH_PARTITION_STORAGE_ENGINE
+  {
+    TABLE_LIST *tbl;
+    for (tbl= select_lex->leaf_tables; tbl; tbl= tbl->next_leaf)
+    {
+      if (!tbl->embedding)
+      {
+        Item *prune_cond= tbl->on_expr? tbl->on_expr : conds;
+        tbl->table->no_partitions_used= prune_partitions(thd, tbl->table,
+	                                                 prune_cond);
+      }
+    }
+  }
+#endif
+
   /* Optimize count(*), min() and max() */
   if (tables_list && tmp_table_param.sum_func_count && ! group_list)
   {
@@ -2018,7 +2033,11 @@ make_join_statistics(JOIN *join, TABLE_LIST *tables, COND *conds,
     if (*s->on_expr_ref)
     {
       /* s is the only inner table of an outer join */
-      if (!table->file->records && !embedding)
+#ifdef WITH_PARTITION_STORAGE_ENGINE
+      if ((!table->file->records || table->no_partitions_used) && !embedding)
+#else
+      if (!table->file->records || && !embedding)
+#endif
       {						// Empty table
         s->dependent= 0;                        // Ignore LEFT JOIN depend.
 	set_position(join,const_count++,s,(KEYUSE*) 0);
@@ -2045,8 +2064,14 @@ make_join_statistics(JOIN *join, TABLE_LIST *tables, COND *conds,
       while (embedding);
       continue;
     }
-
-    if ((table->s->system || table->file->records <= 1) && ! s->dependent &&
+#ifdef WITH_PARTITION_STORAGE_ENGINE
+    bool no_partitions_used= table->no_partitions_used;
+#else
+    const bool no_partitions_used= FALSE;
+#endif
+    if ((table->s->system || table->file->records <= 1 ||
+         no_partitions_used) &&
+	!s->dependent &&
 	!(table->file->table_flags() & HA_NOT_EXACT_COUNT) &&
         !table->fulltext_searched)
     {
@@ -13767,6 +13792,9 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
 					strlen(join->select_lex->type), cs));
     for (uint i=0 ; i < 7; i++)
       item_list.push_back(item_null);
+    if (join->thd->lex->describe & DESCRIBE_PARTITIONS)
+      item_list.push_back(item_null);
+  
     item_list.push_back(new Item_string(message,strlen(message),cs));
     if (result->send_data(item_list))
       join->error= 1;
@@ -13887,7 +13915,28 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
 	item_list.push_back(new Item_string(table->alias,
 					    strlen(table->alias),
 					    cs));
-      /* type */
+      /* "partitions" column */
+      if (join->thd->lex->describe & DESCRIBE_PARTITIONS)
+      {
+#ifdef WITH_PARTITION_STORAGE_ENGINE
+        partition_info *part_info;
+        if (!table->derived_select_number && 
+            (part_info= table->part_info))
+        {          
+          char parts_buff[128]; 
+          String parts_str(parts_buff,sizeof(parts_buff),cs);
+          make_used_partitions_str(part_info, &parts_str);
+          item_list.push_back(new Item_string(parts_str.ptr(),
+                                              parts_str.length(), cs));
+        }
+        else
+          item_list.push_back(item_null);
+#else
+        /* just produce empty column if partitioning is not compiled in */
+        item_list.push_back(item_null); 
+#endif
+      }
+      /* "type" column */
       item_list.push_back(new Item_string(join_type_str[tab->type],
 					  strlen(join_type_str[tab->type]),
 					  cs));

sql/sql_yacc.yy

@@ -7380,8 +7380,10 @@ describe_command:
 opt_extended_describe:
 	/* empty */ {}
 	| EXTENDED_SYM { Lex->describe|= DESCRIBE_EXTENDED; }
+	| PARTITIONS_SYM { Lex->describe|= DESCRIBE_PARTITIONS; }
 	;
 
+
 opt_describe_column:
 	/* empty */	{}
 	| text_string	{ Lex->wild= $1; }