MySQL的select @@identity是什么意思？

@@identity返回当前会话中自增列中最后插入的值。让我们先创建一个表 −

mysql> create table DemoTable(
   UserId int NOT NULL AUTO_INCREMENT PRIMARY KEY,
   UserName varchar(100)
);
Query OK, 0 rows affected (0.67 sec)

使用insert命令向表中插入一些记录 −

mysql> insert into DemoTable(UserName) values('David');
Query OK, 1 row affected (0.15 sec)
mysql> insert into DemoTable(UserName) values('Mike');
Query OK, 1 row affected (0.17 sec)
mysql> insert into DemoTable(UserName) values('Carol');
Query OK, 1 row affected (0.12 sec)
mysql> insert into DemoTable(UserName) values('Robert');
Query OK, 1 row affected (0.24 sec)
mysql> insert into DemoTable(UserName) values('John');
Query OK, 1 row affected (0.13 sec)

使用select语句显示表中的所有记录 −

mysql> select *from DemoTable;

这将产生以下输出结果−

+--------+----------+
| UserId | UserName |
+--------+----------+
| 1      | David    |
| 2      | Mike     | 
| 3      | Carol    |
| 4      | Robert   |
| 5      | John     |
+--------+----------+
5 rows in set (0.00 sec)

现在，我们将使用@@identity −

mysql> select @@identity;

这将产生以下输出结果−

+------------+
| @@identity |
+------------+
| 5          |
+------------+
1 row in set (0.00 sec)

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