Bug#38999 valgrind warnings for update statement in function compare_record()

(InnoDB plugin branch)

mysql-test/suite/innodb_plugin/r/innodb_mysql.result:
  test case
mysql-test/suite/innodb_plugin/t/innodb_mysql.test:
  test case
storage/innodb_plugin/row/row0sel.c:
  init null bytes with default values as they might be
  left uninitialized in some cases and these uninited bytes
  might be copied into mysql record buffer that leads to
  valgrind warnings on next use of the buffer.

mysql-test/suite/innodb_plugin/r/innodb_mysql.result

@@ -2378,4 +2378,16 @@ SELECT SECOND(c)-@bug47453 FROM t1 JOIN t2 ON d=a;
 SECOND(c)-@bug47453
 0
 DROP TABLE t1, t2;
+#
+# Bug#38999 valgrind warnings for update statement in function compare_record()
+#
+CREATE TABLE t1 (a INT PRIMARY KEY) ENGINE=InnoDB;
+CREATE TABLE t2 (a INT PRIMARY KEY) ENGINE=InnoDB;
+INSERT INTO t1 values (1),(2),(3),(4),(5);
+INSERT INTO t2 values (1);
+SELECT * FROM t1 WHERE a = 2;
+a
+2
+UPDATE t1,t2 SET t1.a = t1.a + 100 WHERE t1.a = 1;
+DROP TABLE t1,t2;
 End of 5.1 tests

mysql-test/suite/innodb_plugin/t/innodb_mysql.test

@@ -618,5 +618,18 @@ SELECT SECOND(c)-@bug47453 FROM t1 JOIN t2 ON d=a;
 
 DROP TABLE t1, t2;
 
+--echo #
+--echo # Bug#38999 valgrind warnings for update statement in function compare_record()
+--echo #
+
+CREATE TABLE t1 (a INT PRIMARY KEY) ENGINE=InnoDB;
+CREATE TABLE t2 (a INT PRIMARY KEY) ENGINE=InnoDB;
+INSERT INTO t1 values (1),(2),(3),(4),(5);
+INSERT INTO t2 values (1);
+
+SELECT * FROM t1 WHERE a = 2;
+UPDATE t1,t2 SET t1.a = t1.a + 100 WHERE t1.a = 1;
+
+DROP TABLE t1,t2;
 
 --echo End of 5.1 tests

storage/innodb_plugin/row/row0sel.c

@@ -2678,6 +2678,12 @@ row_sel_store_mysql_rec(
 		prebuilt->blob_heap = NULL;
 	}
 
+	/* init null bytes with default values as they might be
+	left uninitialized in some cases and these uninited bytes
+	might be copied into mysql record buffer that leads to
+	valgrind warnings */
+	memcpy(mysql_rec, prebuilt->default_rec, prebuilt->null_bitmap_len);
+
 	for (i = 0; i < prebuilt->n_template; i++) {
 
 		templ = prebuilt->mysql_template + i;