Parse the SQL statement to obtain the id of the inserted data.

LAST_INSERT_ID:
LAST_INSERT_ID is table-independent. If you insert data to table a and then insert data to table B, LAST_INSERT_ID will change.
Max (id) is obviously unavailable when multiple users insert data alternately.

This should use LAST_INSERT_ID, because LAST_INSERT_ID is based on Connection, as long as each thread uses an independent Connection object, the LAST_INSERT_ID function returns the ID of the first record generated by the Connection for the latest insert or update * of the AUTO_INCREMENT column. This value cannot be affected by connections of other clients. This ensures that you can retrieve your own ID without worrying about the activity of other clients and do not need to lock the client. INSERT multiple records using a single INSERT statement. LAST_INSERT_ID returns a list.

You can use SELECT last_insert_id (); to query the value of LAST_INSERT_ID.
Important: If you insert multiple rows using a single INSERT statement, LAST_INSERT_ID () returns the value generated for the first inserted row only.
INSERT multiple records using a single INSERT statement. LAST_INSERT_ID only returns the value of the first inserted record. For example:

Mysql> insert into t VALUES (NULL, 'aaa'), (NULL, 'bbbbb'), (NULL, 'cccc ');
Mysql> SELECT * FROM t;
+ ---- + ------ +
| Id | name |
+ ---- + ------ +
| 1 | Bob |
| 2 | aaaa |
| 3 | bbbb |
| 4 | cccc |
+ ---- + ------ +
Mysql> SELECT LAST_INSERT_ID ();
+ ------------------ +
| LAST_INSERT_ID () |
+ ------------------ +
| 2 |
+ ------------------ +
ID 2 is generated when the first record aaaa is inserted.
Select @ IDENTITY:
String SQL = "select @ IDENTITY ";
@ Identity refers to the value of the auto-incrementing column corresponding to the last time data is inserted into a table with the identity attribute (that is, the auto-incrementing column). It is a global variable defined by the system. Generally, global variables defined by the system start with @ and User-Defined variables start. For example, if the auto-increment column of Table A is id, after A row of data is inserted into Table A, if the value of the auto-increment column is automatically increased to 101 after the data is inserted, the value obtained through select @ identity is 101.The premise of using @ identity is that the connection is not closed when select @ identity is executed after the insert operation. Otherwise, the value is NULL.