Extended fix for the bug#29555.

The get_time_value function is added. It is used to obtain TIME values both
from items the can return time as an integer and from items that can return
time only as a string.
The Arg_comparator::compare_datetime function now uses pointer to a getter
function to obtain values to compare. Now this function is also used for
comparison of TIME values.
The get_value_func variable is added to the Arg_comparator class.
It points to a getter function for the DATE/DATETIME/TIME comparator.

mysql-test/r/type_time.result

@@ -103,6 +103,12 @@ cast('100:55:50' as time) > cast('024:00:00' as time)
 select cast('300:55:50' as time) > cast('240:00:00' as time);
 cast('300:55:50' as time) > cast('240:00:00' as time)
 1
+create table t1 (f1 time);
+insert into t1 values ('24:00:00');
+select cast('24:00:00' as time) = (select f1 from t1);
+cast('24:00:00' as time) = (select f1 from t1)
+1
+drop table t1;
 create table t1(f1 time, f2 time);
 insert into t1 values('20:00:00','150:00:00');
 select 1 from t1 where cast('100:00:00' as time) between f1 and f2;

mysql-test/t/type_time.test

@@ -50,6 +50,10 @@ select cast('300:55:50' as time) < cast('240:00:00' as time);
 select cast('100:55:50' as time) > cast('24:00:00' as time);
 select cast('100:55:50' as time) > cast('024:00:00' as time);
 select cast('300:55:50' as time) > cast('240:00:00' as time);
+create table t1 (f1 time);
+insert into t1 values ('24:00:00');
+select cast('24:00:00' as time) = (select f1 from t1);
+drop table t1;
 
 #
 # Bug#29739: Incorrect time comparison in BETWEEN.

sql/item_cmpfunc.cc

@@ -666,6 +666,68 @@ Arg_comparator::can_compare_as_dates(Item *a, Item *b, ulonglong *const_value)
 }
 
 
+/*
+  Retrieves correct TIME value from the given item.
+
+  SYNOPSIS
+    get_time_value()
+    thd                 thread handle
+    item_arg   [in/out] item to retrieve TIME value from
+    cache_arg  [in/out] pointer to place to store the caching item to
+    warn_item  [in]     unused
+    is_null    [out]    TRUE <=> the item_arg is null
+
+  DESCRIPTION
+    Retrieves the correct TIME value from given item for comparison by the
+    compare_datetime() function.
+    If item's result can be compared as longlong then its int value is used
+    and a value returned by get_time function is used otherwise.
+    If an item is a constant one then its value is cached and it isn't
+    get parsed again. An Item_cache_int object is used for caching values. It
+    seamlessly substitutes the original item.  The cache item is marked as
+    non-constant to prevent re-caching it again.
+
+  RETURN
+    obtained value
+*/
+
+ulonglong
+get_time_value(THD *thd, Item ***item_arg, Item **cache_arg,
+               Item *warn_item, bool *is_null)
+{
+  ulonglong value;
+  Item *item= **item_arg;
+  MYSQL_TIME ltime;
+
+  if (item->result_as_longlong())
+  {
+    value= item->val_int();
+    *is_null= item->null_value;
+  }
+  else
+  {
+    *is_null= item->get_time(&ltime);
+    if (!is_null)
+      value= TIME_to_ulonglong_datetime(&ltime);
+  }
+  /*
+    Do not cache GET_USER_VAR() function as its const_item() may return TRUE
+    for the current thread but it still may change during the execution.
+  */
+  if (item->const_item() && cache_arg && (item->type() != Item::FUNC_ITEM ||
+      ((Item_func*)item)->functype() != Item_func::GUSERVAR_FUNC))
+  {
+    Item_cache_int *cache= new Item_cache_int();
+    /* Mark the cache as non-const to prevent re-caching. */
+    cache->set_used_tables(1);
+    cache->store(item, value);
+    *cache_arg= cache;
+    *item_arg= cache_arg;
+  }
+  return value;
+}
+
+
 int Arg_comparator::set_cmp_func(Item_bool_func2 *owner_arg,
                                         Item **a1, Item **a2,
                                         Item_result type)
@@ -704,6 +766,7 @@ int Arg_comparator::set_cmp_func(Item_bool_func2 *owner_arg,
     }
     is_nulls_eq= test(owner && owner->functype() == Item_func::EQUAL_FUNC);
     func= &Arg_comparator::compare_datetime;
+    get_value_func= &get_datetime_value;
     return 0;
   }
   else if (type == STRING_RESULT && (*a)->field_type() == MYSQL_TYPE_TIME &&
@@ -712,9 +775,11 @@ int Arg_comparator::set_cmp_func(Item_bool_func2 *owner_arg,
     /* Compare TIME values as integers. */
     thd= current_thd;
     owner= owner_arg;
-    func= ((test(owner && owner->functype() == Item_func::EQUAL_FUNC)) ?
-           &Arg_comparator::compare_e_int :
-           &Arg_comparator::compare_int_unsigned);
+    a_cache= 0;
+    b_cache= 0;
+    is_nulls_eq= test(owner && owner->functype() == Item_func::EQUAL_FUNC);
+    func= &Arg_comparator::compare_datetime;
+    get_value_func= &get_time_value;
     return 0;
   }
 
@@ -735,8 +800,10 @@ void Arg_comparator::set_datetime_cmp_func(Item **a1, Item **b1)
   b_cache= 0;
   is_nulls_eq= FALSE;
   func= &Arg_comparator::compare_datetime;
+  get_value_func= &get_datetime_value;
 }
 
+
 /*
   Retrieves correct DATETIME value from given item.
 
@@ -850,8 +917,8 @@ int Arg_comparator::compare_datetime()
   bool is_null= FALSE;
   ulonglong a_value, b_value;
 
-  /* Get DATE/DATETIME value of the 'a' item. */
-  a_value= get_datetime_value(thd, &a, &a_cache, *b, &is_null);
+  /* Get DATE/DATETIME/TIME value of the 'a' item. */
+  a_value= (*get_value_func)(thd, &a, &a_cache, *b, &is_null);
   if (!is_nulls_eq && is_null)
   {
     if (owner)
@@ -859,8 +926,8 @@ int Arg_comparator::compare_datetime()
     return -1;
   }
 
-  /* Get DATE/DATETIME value of the 'b' item. */
-  b_value= get_datetime_value(thd, &b, &b_cache, *a, &is_null);
+  /* Get DATE/DATETIME/TIME value of the 'b' item. */
+  b_value= (*get_value_func)(thd, &b, &b_cache, *a, &is_null);
   if (is_null)
   {
     if (owner)

sql/item_cmpfunc.h

@@ -42,6 +42,8 @@ class Arg_comparator: public Sql_alloc
   bool is_nulls_eq;                // TRUE <=> compare for the EQUAL_FUNC
   enum enum_date_cmp_type { CMP_DATE_DFLT= 0, CMP_DATE_WITH_DATE,
                             CMP_DATE_WITH_STR, CMP_STR_WITH_DATE };
+  ulonglong (*get_value_func)(THD *thd, Item ***item_arg, Item **cache_arg,
+                              Item *warn_item, bool *is_null);
 public:
   DTCollation cmp_collation;