lp:737092 Assertion `item->null_value' failed in get_datetime_value in 5.1-micro

Implement Item_func_coalesce::get_date()

mysql-test/r/func_time.result

@@ -1494,3 +1494,6 @@ least(1, f1)
 Warnings:
 Warning	1292	Incorrect datetime value: '1' for column 'f1' at row 1
 drop table t1;
+select now() > coalesce(time('21:43:24'), date('2010-05-03'));
+now() > coalesce(time('21:43:24'), date('2010-05-03'))
+1

mysql-test/t/func_time.test

@@ -932,3 +932,9 @@ create table t1 (f1 timestamp);
 insert into t1 values ('0000-00-00 00:00:00');
 select least(1, f1) from t1;
 drop table t1;
+
+#
+# lp:737092 Assertion `item->null_value' failed in get_datetime_value in 5.1-micro
+#
+select now() > coalesce(time('21:43:24'), date('2010-05-03'));
+

sql/item_cmpfunc.cc

@@ -2901,6 +2901,21 @@ double Item_func_coalesce::real_op()
 }
 
 
+bool Item_func_coalesce::get_date(MYSQL_TIME *ltime,uint fuzzydate)
+{
+  DBUG_ASSERT(fixed == 1);
+  null_value= 0;
+  for (uint i= 0; i < arg_count; i++)
+  {
+    bool res= args[i]->get_date(ltime, fuzzydate);
+    if (!args[i]->null_value)
+      return res;
+  }
+  null_value=1;
+  return 0;
+}
+
+
 my_decimal *Item_func_coalesce::decimal_op(my_decimal *decimal_value)
 {
   DBUG_ASSERT(fixed == 1);

sql/item_cmpfunc.h

@@ -675,6 +675,7 @@ public:
   const char *func_name() const { return "coalesce"; }
   table_map not_null_tables() const { return 0; }
   enum_field_types field_type() const { return cached_field_type; }
+  bool get_date(MYSQL_TIME *ltime,uint fuzzydate);
 };