MySQL: Insert record if not exists in table

Question

Hi, I am trying to execute the following query:

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

But this returns an error. Basically I don't want to insert a record if the 'name' field of the record already exists in another record - how to check if the new name is unique?

Answer 1

what about defining the field "name" as unique?

Otherwise use the keyword "IN" in your query

Answer 2

You are inserting not Updating the result. You can define the name column in primary column or set it is unique.

Answer 3

INSERT doesn't allow WHERE in the syntax.

What you can do: create a UNIQUE INDEX on the field which should be unique (name), then use either:

• normal INSERT (and handle the error if the name already exists)
• INSERT IGNORE (which will fail silently cause a warning (instead of error) if name already exists)
• INSERT ... ON DUPLICATE KEY UPDATE (which will execute the UPDATE at the end if name already exists, see documentation)

Answer 4

I'm not actually suggesting that you do this, as the UNIQUE index as suggested by Piskvor and others is a far better way to do it, but you can actually do what you were attempting:

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;

Insert a record:

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  |
+----+--------+-----------+------+

Try to insert the same record again:

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  |
+----+--------+-----------+------+

Insert a different record:

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  |
+----+--------+-----------+------+

And so on...

Answer 5

If you really can't get a unique index on the table, you could try...

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