MySQL：如果表中不存在则插入记录

发布于07月02日

我正在try 执行以下查询:

INSERT INTO table_listnames (name, address, tele)
VALUES ('Rupert', 'Somewhere', '022')
WHERE NOT EXISTS (
    SELECT name FROM table_listnames WHERE name='value'
);

但这会返回一个错误.基本上，如果记录的"名称"字段已经存在于另一个记录中，我不想插入记录——如何判断新名称是否唯一？

推荐答案

我并不是真的建议你这么做，因为Piskvor和其他人建议的UNIQUE指数是一种更好的方法，但你实际上可以做你试图做的事情:

CREATE TABLE `table_listnames` (
  `id` int(11) NOT NULL auto_increment,
  `name` varchar(255) NOT NULL,
  `address` varchar(255) NOT NULL,
  `tele` varchar(255) NOT NULL,
  PRIMARY KEY  (`id`)
) ENGINE=InnoDB;

插入一条记录:

INSERT INTO table_listnames (name, address, tele)
SELECT * FROM (SELECT 'Rupert', 'Somewhere', '022') AS tmp
WHERE NOT EXISTS (
    SELECT name FROM table_listnames WHERE name = 'Rupert'
) LIMIT 1;

Query OK, 1 row affected (0.00 sec)
Records: 1  Duplicates: 0  Warnings: 0

SELECT * FROM `table_listnames`;

+----+--------+-----------+------+
| id | name   | address   | tele |
+----+--------+-----------+------+
|  1 | Rupert | Somewhere | 022  |
+----+--------+-----------+------+

再次try 插入相同的记录:

INSERT INTO table_listnames (name, address, tele)
SELECT * FROM (SELECT 'Rupert', 'Somewhere', '022') AS tmp
WHERE NOT EXISTS (
    SELECT name FROM table_listnames WHERE name = 'Rupert'
) LIMIT 1;

Query OK, 0 rows affected (0.00 sec)
Records: 0  Duplicates: 0  Warnings: 0

+----+--------+-----------+------+
| id | name   | address   | tele |
+----+--------+-----------+------+
|  1 | Rupert | Somewhere | 022  |
+----+--------+-----------+------+

插入其他记录:

INSERT INTO table_listnames (name, address, tele)
SELECT * FROM (SELECT 'John', 'Doe', '022') AS tmp
WHERE NOT EXISTS (
    SELECT name FROM table_listnames WHERE name = 'John'
) LIMIT 1;

Query OK, 1 row affected (0.00 sec)
Records: 1  Duplicates: 0  Warnings: 0

SELECT * FROM `table_listnames`;

+----+--------+-----------+------+
| id | name   | address   | tele |
+----+--------+-----------+------+
|  1 | Rupert | Somewhere | 022  |
|  2 | John   | Doe       | 022  |
+----+--------+-----------+------+

等等

更新:

为了防止两个值相等时出现#1060 - Duplicate column name错误，必须将内部 Select 的列命名为:

INSERT INTO table_listnames (name, address, tele)
SELECT * FROM (SELECT 'Unknown' AS name, 'Unknown' AS address, '022' AS tele) AS tmp
WHERE NOT EXISTS (
    SELECT name FROM table_listnames WHERE name = 'Rupert'
) LIMIT 1;

Query OK, 1 row affected (0.00 sec)
Records: 1  Duplicates: 0  Warnings: 0

SELECT * FROM `table_listnames`;

+----+---------+-----------+------+
| id | name    | address   | tele |
+----+---------+-----------+------+
|  1 | Rupert  | Somewhere | 022  |
|  2 | John    | Doe       | 022  |
|  3 | Unknown | Unknown   | 022  |
+----+---------+-----------+------+