MDEV-18503 Assertion `native.length() == binlen' failed in...

MDEV-18503 Assertion `native.length() == binlen' failed in Type_handler_timestamp_common::make_sort_key

mysql-test/main/type_timestamp.result

@@ -1251,5 +1251,21 @@ Warning	1292	Incorrect datetime value: '1' for column `test`.`t1`.`f` at row 1
 Warning	1292	Incorrect datetime value: '2' for column `test`.`t1`.`f` at row 2
 DROP TABLE t1;
 #
+# MDEV-18503 Assertion `native.length() == binlen' failed in Type_handler_timestamp_common::make_sort_key
+#
+SET sql_mode='';
+CREATE TABLE t1 (a TIMESTAMP(3) DEFAULT 0, b TIMESTAMP);
+INSERT INTO t1 (b) VALUES ('2012-12-12 12:12:12'),('1988-08-26 12:12:12');
+SELECT GREATEST(a,b) AS f FROM t1 ORDER BY 1;
+f
+1988-08-26 12:12:12.000
+2012-12-12 12:12:12.000
+SELECT GREATEST(a,b) AS f FROM t1 ORDER BY 1 DESC;
+f
+2012-12-12 12:12:12.000
+1988-08-26 12:12:12.000
+DROP TABLE t1;
+SET sql_mode=DEFAULT;
+#
 # End of 10.4 tests
 #

mysql-test/main/type_timestamp.test

@@ -825,6 +825,18 @@ SELECT * FROM t1 WHERE f IN (DEFAULT(t),1);
 DROP TABLE t1;
 
 
+--echo #
+--echo # MDEV-18503 Assertion `native.length() == binlen' failed in Type_handler_timestamp_common::make_sort_key
+--echo #
+
+SET sql_mode='';
+CREATE TABLE t1 (a TIMESTAMP(3) DEFAULT 0, b TIMESTAMP);
+INSERT INTO t1 (b) VALUES ('2012-12-12 12:12:12'),('1988-08-26 12:12:12');
+SELECT GREATEST(a,b) AS f FROM t1 ORDER BY 1;
+SELECT GREATEST(a,b) AS f FROM t1 ORDER BY 1 DESC;
+DROP TABLE t1;
+SET sql_mode=DEFAULT;
+
 --echo #
 --echo # End of 10.4 tests
 --echo #

sql/filesort.cc

@@ -1067,8 +1067,9 @@ Type_handler_timestamp_common::make_sort_key(uchar *to, Item *item,
                                              const SORT_FIELD_ATTR *sort_field,
                                              Sort_param *param) const
 {
+  THD *thd= current_thd;
   uint binlen= my_timestamp_binary_length(item->decimals);
-  Timestamp_or_zero_datetime_native_null native(current_thd, item);
+  Timestamp_or_zero_datetime_native_null native(thd, item);
   if (native.is_null() || native.is_zero_datetime())
   {
     // NULL or '0000-00-00 00:00:00'
@@ -1076,9 +1077,19 @@ Type_handler_timestamp_common::make_sort_key(uchar *to, Item *item,
   }
   else
   {
-    DBUG_ASSERT(native.length() == binlen);
     if (item->maybe_null)
       *to++= 1;
+    if (native.length() != binlen)
+    {
+      /*
+        Some items can return native representation with a different
+        number of fractional digits, e.g.: GREATEST(ts_3, ts_4) can
+        return a value with 3 fractional digits, although its fractional
+        precision is 4. Re-pack with a proper precision now.
+      */
+      Timestamp(native).to_native(&native, item->datetime_precision(thd));
+    }
+    DBUG_ASSERT(native.length() == binlen);
     memcpy((char *) to, native.ptr(), binlen);
   }
 }