MySQL 如何仅插入MySQL表中不存在的记录

要插入不存在的记录，请将列设置为UNIQUE INDEX。让我们首先创建一个表−

mysql> create table DemoTable
   (
   Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,
   FirstName varchar(20)
   );
Query OK, 0 rows affected (0.30 sec)

以下是创建唯一索引以插入不存在于’FirstName’列中的记录的查询 −

mysql> CREATE UNIQUE INDEX index_on_FirstName ON DemoTable(FirstName);
Query OK, 0 rows affected (0.56 sec)
Records: 0 Duplicates: 0 Warnings: 0

使用insert命令在表中插入一些记录。现在，您可以检查insert命令仅插入不存在的那些记录 –

mysql> insert into DemoTable(FirstName) values('Chris');
Query OK, 1 row affected (0.07 sec)

mysql> insert into DemoTable(FirstName) values('Chris');
ERROR 1062 (23000): Duplicate entry 'Chris' for key 'index_on_FirstName'
mysql>
mysql> insert into DemoTable(FirstName) values('Robert');
Query OK, 1 row affected (0.04 sec)

mysql> insert into DemoTable(FirstName) values('Mike');
Query OK, 1 row affected (0.04 sec)

mysql> insert into DemoTable(FirstName) values('Robert');
ERROR 1062 (23000): Duplicate entry 'Robert' for key 'index_on_FirstName'
mysql>

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 −

+----+-----------+
| Id | FirstName |
+----+-----------+
|  1 | Chris     |
|  2 | Robert    |
|  3 | Mike      |
+----+-----------+
3 rows in set (0.00 sec)

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