Question

I have a table user. It has columns id and email.

USER TABLE

id | email
1  | [e-mail]
2  | [e-mail]

The id is a PRIMARY KEY AUTO_INCREMENT and the email is an UNIQUE KEY.
When I insert a new row in the table and there is a DUPLICATE KEY exception thrown. I want to fetch the id on which the DUPLICATE KEY exception was thrown.

Right now I am doing this –

BEGIN
DECLARE EXIT HANDLER FOR 1062
    BEGIN
        SELECT id
        INTO id
        FROM user
        WHERE email = '[e-mail]';
    END;
    INSERT INTO user
    (email)
    VALUES
    ('[e-mail]');

SELECT LAST_INSERT_ID() INTO id;
END;

I want to know if there is a better way to do this. That is to avoid scanning the table again to get the id for which it had already scanned to check the uniqueness of the email.

Answer 1

Use INSERT ... ON DUPLICATE KEY UPDATE, then get the autoincremented id as usual:

If a table contains an AUTO_INCREMENT column and INSERT ... ON DUPLICATE KEY UPDATE inserts or updates a row, the LAST_INSERT_ID() function returns the AUTO_INCREMENT value. Exception: For updates, LAST_INSERT_ID() is not meaningful prior to MySQL 5.1.12. However, you can work around this by using LAST_INSERT_ID(expr). Suppose that id is the AUTO_INCREMENT column. To make LAST_INSERT_ID() meaningful for updates, insert rows as follows:

INSERT INTO table (a,b,c) VALUES (1,2,3)
  ON DUPLICATE KEY UPDATE id=LAST_INSERT_ID(id), c=3;