WL#2985 "Partition pruning", postreview fixes: Small code fixes and better comments

mysql-test/r/partition.result:
  Added testcase for BUG#15819
mysql-test/t/partition.test:
  Added testcase for BUG#15819
sql/item.h:
  WL#2985 "Partition pruning", postreview fixes: better comments
sql/item_timefunc.cc:
  WL#2985 "Partition pruning", postreview fixes: better comments
sql/opt_range.cc:
  WL#2985 "Partition pruning", postreview fixes: 
  - better comments, local function renames
  - Made SEL_ARG::is_singlepoint() to correctly handle NULL edge values.
  - fix uninitialized variable access: s/res |=/res =/
sql/sql_class.cc:
  WL#2985 "Partition pruning", postreview fixes: 
  Set correct max. length of "partitions" column in EXPLAIN output
sql/sql_lex.h:
  WL#2985 "Partition pruning", postreview fixes: better comments
sql/sql_partition.cc:
  WL#2985 "Partition pruning", postreview fixes: better comments

mysql-test/r/partition.result

@@ -148,3 +148,10 @@ t1	CREATE TABLE `t1` (
   `b` int(11) default NULL
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1 PARTITION BY RANGE (a) (PARTITION x1 VALUES LESS THAN (6) ENGINE = MyISAM, PARTITION x3 VALUES LESS THAN (8) ENGINE = MyISAM, PARTITION x4 VALUES LESS THAN (10) ENGINE = MyISAM, PARTITION x5 VALUES LESS THAN (12) ENGINE = MyISAM, PARTITION x6 VALUES LESS THAN (14) ENGINE = MyISAM, PARTITION x7 VALUES LESS THAN (16) ENGINE = MyISAM, PARTITION x8 VALUES LESS THAN (18) ENGINE = MyISAM, PARTITION x9 VALUES LESS THAN (20) ENGINE = MyISAM)
 drop table t1;
+create table t1 (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 t1 values (10,1);
+ERROR HY000: Table has no partition for value 11
+drop table t1;

mysql-test/t/partition.test

@@ -203,3 +203,14 @@ ALTER TABLE t1 REORGANISE PARTITION x0,x1,x2 INTO
 (PARTITION x1 VALUES LESS THAN (6));
 show create table t1;
 drop table t1;
+
+# Testcase for BUG#15819
+create table t1 (a int not null, b int not null) partition by LIST (a+b) (
+  partition p0 values in (12),
+  partition p1 values in (14)
+);
+--error 1500
+insert into t1 values (10,1);
+
+drop table t1;
+

sql/item.h

@@ -381,13 +381,20 @@ class Name_resolution_context_state
     put values of field_i into table record buffer;
     return item->val_int(); 
   }
+
+  NOTE
+  At the moment function monotonicity is not well defined (and so may be
+  incorrect) for Item trees with parameters/return types that are different
+  from INT_RESULT, may be NULL, or are unsigned.
+  It will be possible to address this issue once the related partitioning bugs
+  (BUG#16002, BUG#15447, BUG#13436) are fixed.
 */
 
 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)" */
+   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;
 
 /*************************************************************************/

sql/item_timefunc.cc

@@ -885,6 +885,21 @@ longlong Item_func_to_days::val_int()
   return (longlong) calc_daynr(ltime.year,ltime.month,ltime.day);
 }
 
+
+/*
+  Get information about this Item tree monotonicity
+
+  SYNOPSIS
+    Item_func_to_days::get_monotonicity_info()
+
+  DESCRIPTION
+  Get information about monotonicity of the function represented by this item
+  tree.
+
+  RETURN
+    See enum_monotonicity_info.
+*/
+
 enum_monotonicity_info Item_func_to_days::get_monotonicity_info() const
 {
   if (args[0]->type() == Item::FIELD_ITEM)
@@ -1080,6 +1095,21 @@ longlong Item_func_year::val_int()
   return (longlong) ltime.year;
 }
 
+
+/*
+  Get information about this Item tree monotonicity
+
+  SYNOPSIS
+    Item_func_to_days::get_monotonicity_info()
+
+  DESCRIPTION
+  Get information about monotonicity of the function represented by this item
+  tree.
+
+  RETURN
+    See enum_monotonicity_info.
+*/
+
 enum_monotonicity_info Item_func_year::get_monotonicity_info() const
 {
   if (args[0]->type() == Item::FIELD_ITEM &&

sql/sql_class.cc

@@ -758,7 +758,10 @@ int THD::send_explain_fields(select_result *result)
 #ifdef WITH_PARTITION_STORAGE_ENGINE
   if (lex->describe & DESCRIBE_PARTITIONS)
   {
-    field_list.push_back(item= new Item_empty_string("partitions", 10, cs));
+    /* Maximum length of string that make_used_partitions_str() can produce */
+    item= new Item_empty_string("partitions", MAX_PARTITIONS * (1 + FN_LEN),
+                                cs);
+    field_list.push_back(item);
     item->maybe_null= 1;
   }
 #endif

sql/sql_lex.h

@@ -104,7 +104,7 @@ enum enum_sql_command {
 #define DESCRIBE_NORMAL		1
 #define DESCRIBE_EXTENDED	2
 /*
-  This is not #ifdef'ed because we want "EXPLAIN PARTITIONS ..." to produce
+  This is not within #ifdef because we want "EXPLAIN PARTITIONS ..." to produce
   additional "partitions" column even if partitioning is not compiled in.
 */
 #define DESCRIBE_PARTITIONS	4

sql/sql_partition.cc

@@ -3467,11 +3467,19 @@ void set_key_field_ptr(KEY *key_info, const byte *new_buf,
 
 
 /*
-  Fill the string comma-separated line of used partitions names
+  Return comma-separated list of used partitions in the provided given string
+
   SYNOPSIS
     make_used_partitions_str()
       part_info  IN  Partitioning info
       parts_str  OUT The string to fill
+
+  DESCRIPTION
+    Generate a list of used partitions (from bits in part_info->used_partitions
+    bitmap), asd store it into the provided String object.
+    
+  NOTE
+    The produced string must not be longer then MAX_PARTITIONS * (1 + FN_LEN).
 */
 
 void make_used_partitions_str(partition_info *part_info, String *parts_str)