From 2fd0bc63bb19b1a691d73ff3d40d613f383238e5 Mon Sep 17 00:00:00 2001
From: Evgeny Potemkin <epotemkin@mysql.com>
Date: Thu, 7 Oct 2010 20:16:30 +0400
Subject: [PATCH] Bug#57095: Wrongly chosen expression cache type led to a
 wrong result. The coalesce function returned DATETIME type due to a DATETIME
 argument, but since it's not a date/time function it can't return correct int
 value for it. Nevertheless Item_datetime_cache was chosen to cache coalesce's
 result and that led to a wrong result.

Now Item_datetime_cache is used only for those function that could return
correct int representation of DATETIME values.
---
 mysql-test/r/type_datetime.result | 12 ++++++++++++
 mysql-test/t/type_datetime.test   | 10 ++++++++++
 sql/item.cc                       |  8 +++++---
 3 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/mysql-test/r/type_datetime.result b/mysql-test/r/type_datetime.result
index f7bfba0accd..958285d6a23 100644
--- a/mysql-test/r/type_datetime.result
+++ b/mysql-test/r/type_datetime.result
@@ -680,5 +680,17 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t2	const	PRIMARY	PRIMARY	8	const	1	Using index
 DROP TABLE t1,t2;
 #
+# Bug#57095: Wrongly chosen expression cache type led to a wrong
+#            result.
+#
+CREATE TABLE t1 (`b` datetime );
+INSERT INTO t1 VALUES ('2010-01-01 00:00:00'), ('2010-01-01 00:00:00');
+SELECT * FROM t1 WHERE b <= coalesce(NULL, now());
+b
+2010-01-01 00:00:00
+2010-01-01 00:00:00
+DROP TABLE t1;
+#
+#
 # End of 5.5 tests
 #
diff --git a/mysql-test/t/type_datetime.test b/mysql-test/t/type_datetime.test
index 6e40c9ccfa0..ca2a7804907 100644
--- a/mysql-test/t/type_datetime.test
+++ b/mysql-test/t/type_datetime.test
@@ -484,6 +484,16 @@ explain select * from t2 where f1=STR_TO_DATE('4/1/2010', '%m/%d/%Y');
 
 DROP TABLE t1,t2;
 
+--echo #
+--echo # Bug#57095: Wrongly chosen expression cache type led to a wrong
+--echo #            result.
+--echo #
+CREATE TABLE t1 (`b` datetime );
+INSERT INTO t1 VALUES ('2010-01-01 00:00:00'), ('2010-01-01 00:00:00');
+SELECT * FROM t1 WHERE b <= coalesce(NULL, now());
+DROP TABLE t1;
+--echo #
+
 --echo #
 --echo # End of 5.5 tests
 --echo #
diff --git a/sql/item.cc b/sql/item.cc
index e782e90b874..fff7511015f 100644
--- a/sql/item.cc
+++ b/sql/item.cc
@@ -7356,9 +7356,11 @@ Item_cache* Item_cache::get_cache(const Item *item, const Item_result type)
   case DECIMAL_RESULT:
     return new Item_cache_decimal();
   case STRING_RESULT:
-    if (item->field_type() == MYSQL_TYPE_DATE ||
-        item->field_type() == MYSQL_TYPE_DATETIME ||
-        item->field_type() == MYSQL_TYPE_TIME)
+    /* Not all functions that return DATE/TIME are actually DATE/TIME funcs. */
+    if ((item->field_type() == MYSQL_TYPE_DATE ||
+         item->field_type() == MYSQL_TYPE_DATETIME ||
+         item->field_type() == MYSQL_TYPE_TIME) &&
+        (const_cast<Item*>(item))->result_as_longlong())
       return new Item_cache_datetime(item->field_type());
     return new Item_cache_str(item);
   case ROW_RESULT: