[opt](datetime) truncate the digits that fall outside the precision range

be/src/vec/runtime/vdatetime_value.cpp

@@ -2067,6 +2067,12 @@ bool DateV2Value<T>::from_date_str_base(const char* date_str, int len, int scale
             break;
         }
 
+        // digits are truncated if they fall outside the max precision range(currently 6),
+        // so that users can still use doris if migrate from other systems that have a larger precision.
+        while (field_idx == 6 && isdigit(*ptr)) {
+            ++ptr;
+        }
+
         // timezone
         if (UNLIKELY((field_idx > 2 ||
                       !has_bar) /*dont treat xxxx-xx-xx:xx:xx as xxxx-xx(-xx:xx:xx)*/

fe/fe-core/src/main/java/org/apache/doris/nereids/trees/expressions/literal/DateLiteral.java

@@ -234,11 +234,15 @@ static String normalize(String s) {
         }
 
         // parse MicroSecond
-        if (partNumber == 6 && i < s.length() && s.charAt(i) == '.') {
-            sb.append(s.charAt(i));
-            i += 1;
+        if (partNumber == 6 && i < s.length() && s.charAt(i - 1) == '.') {
+            // digits are truncated if they fall outside the max precision range(currently 6),
+            // so that users can still use doris if migrate from other systems that have a larger precision.
+            int idx = 0;
             while (i < s.length() && Character.isDigit(s.charAt(i))) {
-                sb.append(s.charAt(i));
+                if (idx < 6) {
+                    sb.append(s.charAt(i));
+                    idx++;
+                }
                 i += 1;
             }
         }

regression-test/data/datatype_p0/datetimev2/test_precision.out

@@ -0,0 +1,50 @@
+-- This file is automatically generated. You should know what you did if you want to edit this
+-- !cast_on_fe --
+2024-02-21T01:23:45.123456
+
+-- !cast_on_fe --
+2024-02-21T09:23:45.123456
+
+-- !cast_on_fe --
+2024-02-21T01:23:45.123456
+
+-- !cast_on_fe --
+2024-02-21T09:23:45.123456
+
+-- !cast_on_fe --
+2024-02-21T01:23:45.123456
+
+-- !cast_on_fe --
+2024-02-21T09:23:45.123456
+
+-- !cast_on_fe --
+2024-02-21T01:23:45.123456
+
+-- !cast_on_fe --
+2024-02-21T09:23:45.123456
+
+-- !cast_on_fe --
+PLAN FRAGMENT 0
+  OUTPUT EXPRS:
+    '2024-02-21 09:23:45.123456'[#0]
+  PARTITION: UNPARTITIONED
+
+  HAS_COLO_PLAN_NODE: false
+
+  VRESULT SINK
+     MYSQL_PROTOCAL
+
+  0:VUNION(34)
+     constant exprs: 
+         '2024-02-21 09:23:45.123456'
+
+-- !sql_all --
+0	2024-02-21T11:11:11	2022-01-01T11:11:11.123456	2024-02-06 03:37:07.123456Z
+1	2024-02-21T11:11:11	2022-01-01T11:11:11.123456	2024-02-06 03:37:07.1234567Z
+2	2024-02-21T11:11:11	2022-01-01T11:11:11.123456	2024-02-06 03:37:07.12345678Z
+
+-- !sql_cast_on_be --
+2024-02-06 03:37:07.123456Z	2024-02-06T11:37:07.123456
+2024-02-06 03:37:07.1234567Z	2024-02-06T11:37:07.123456
+2024-02-06 03:37:07.12345678Z	2024-02-06T11:37:07.123456
+

regression-test/suites/datatype_p0/datetimev2/test_precision.groovy

@@ -0,0 +1,65 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+suite("test_datetime_precision") {
+    sql "set enable_fallback_to_original_planner=false;"
+    qt_cast_on_fe "select cast ('2024-02-21 01:23:45.123456' as Datetime(6));"
+    qt_cast_on_fe "select cast ('2024-02-21 01:23:45.123456Z' as Datetime(6));"
+    qt_cast_on_fe "select cast ('2024-02-21T01:23:45.123456' as Datetime(6));"
+    qt_cast_on_fe "select cast ('2024-02-21T01:23:45.123456Z' as Datetime(6));"
+
+    qt_cast_on_fe "select cast ('2024-02-21 01:23:45.1234567' as Datetime(6));"
+    qt_cast_on_fe "select cast ('2024-02-21 01:23:45.1234567Z' as Datetime(6));"
+    qt_cast_on_fe "select cast ('2024-02-21T01:23:45.1234567' as Datetime(6));"
+    qt_cast_on_fe "select cast ('2024-02-21T01:23:45.1234567Z' as Datetime(6));"
+    // make sure expr if folded on FE (result should not contain cast expr)
+    qt_cast_on_fe "explain select cast ('2024-02-21T01:23:45.1234567Z' as Datetime(6));"
+
+
+    sql "drop table if exists test_datetime_precision;"
+    sql """
+    CREATE TABLE IF NOT EXISTS test_datetime_precision (
+      `rowid` int,
+      `col1` datetimev2 NULL COMMENT "",
+      `col2` datetimev2(6) NULL COMMENT "",
+      `str` VARCHAR NOT NULL
+    ) ENGINE=OLAP
+    DISTRIBUTED BY HASH(`rowid`) BUCKETS 2
+    PROPERTIES (
+    "replication_allocation" = "tag.location.default: 1",
+    "in_memory" = "false",
+    "storage_format" = "V2");
+    """
+
+    // constants in values will be folded on FE
+    sql """
+    insert into test_datetime_precision values
+    (0, '2024-02-21 11:11:11.123456', '2022-01-01 11:11:11.123456', '2024-02-06 03:37:07.123456Z'),
+    (1, '2024-02-21 11:11:11.1234567', '2022-01-01 11:11:11.1234567', '2024-02-06 03:37:07.1234567Z'),
+    (2, '2024-02-21 11:11:11.12345678', '2022-01-01 11:11:11.12345678', '2024-02-06 03:37:07.12345678Z');
+    """
+
+    qt_sql_all """
+    select * from test_datetime_precision order by rowid, str desc;
+    """
+
+    qt_sql_cast_on_be """
+    select t1.str as original_str, cast(str as Datetime(6)) from test_datetime_precision t1 order by str desc;
+    """
+
+
+}