dml : fix last insert id when autoid specified by user in first row. (#11973)

[sre-bot]

cherry-pick #11973 to release-2.1

---

What problem does this PR solve?

Fix last insert id when autoid specified by user in first row.
Table

mysql> desc t;
+-------+---------+------+------+---------+----------------+
| Field | Type    | Null | Key  | Default | Extra          |
+-------+---------+------+------+---------+----------------+
| a     | int(11) | NO   | PRI  | NULL    | auto_increment |
| b     | int(11) | YES  |      | NULL    |                |
+-------+---------+------+------+---------+----------------+
2 rows in set (0.00 sec)

before this PR

mysql> insert into t values(300000, -1),(null, -1),(null, -1);
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> select last_insert_id();
+------------------+
| last_insert_id() |
+------------------+
|                0 |
+------------------+
1 row in set (0.00 sec)

After this PR = MySQL's behavior

mysql> insert into t values(300000, -1),(null, -1),(null, -1);
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> select last_insert_id();
+------------------+
| last_insert_id() |
+------------------+
|           300001 |
+------------------+
1 row in set (0.00 sec)

What is changed and how it works?

Last insert id is not strong lied with the first insert row.
More specifically, it does lie with the first row that without user specified autoID.

Change the judging logic, 0 is inited value meaning that last insert id hasn't be assigned. So do the assignment under the condition.

Check List

Tests

• Unit test
• Integration test

Related changes

• Need to cherry-pick to the release branch

Release note

• fix last insert id when autoid specified by user in first row.

[sre-bot]

/run-all-tests

[AilinKid]

/rebuild

[AilinKid]

/run-all-tests