Question

I’m using PHP and I need to insert a new record in a MySQL DB or if it exists simply update it. I read several answers where they propose to use REPLACE or INSERT...ON DUPLICATE KEY UPDATE, however if I well understood, these two option imply the use of unique fields or primary keys (that are unique). In my case the MySQL table has values similar to this:

Timestamp            | Query1   | Query2   | Result
-------------------------------------------------------- 
2012-10-13 08:15:27  | American | Men      | here result

2012-10-13 08:15:23  | American | Men      | result2

2012-10-13 08:15:27  | American | Women    | other result

2012-10-13 08:15:27  | German   | Men      | here result

Therefore I cannot have primary keys or univoque fields since “query1”, “query2” and “Result” can have the same values (e.g. I can have several records with more fields containing “American” (query1) and “Men” (query2) and different results.

At the moment in PHP I’m using:

INSERT INTO results (Timestamp, Query1, Query2, Result) VALUES ('$current_timestamp', '$nationality', '$gender', '')

Which just append all the records and create a huge DB. But what I want to achieve is adding a new record just if the entire combination query1&query2&result doesn’t exist. Otherwise I just want to update the “timestamp” field.

For instance if my PHP script produces the following data:

Timestamp            | Query1   | Query2   | Result
2012-10-13 08:15:23  | American | Men      | result2

and the database already contains this exact combination of “American”&”Men”&”result2” then just the field “timestamp” is updated. Otherwise, if the combination is different (e.g. “American” “Men” “result3) a new record is added to the table.

Thank you in advance for your help

Answer 1

Even absent a single PRIMARY KEY column like a typical AUTO_INCREMENT integer, if those three columns are meant to be a unique combination you ought to define them as a composite key . This will not only preserve uniqueness but also enforce indexing on them as a unit.

CREATE TABLE results (
  `Timestamp` DATETIME NOT NULL,
  `Query1` VARCHAR() NOT NULL,
  `Query2` VARCHAR() NOT NULL,
  `Result` VARCHAR() NOT NULL,
  /* Composite key across three columns */
  PRIMARY KEY (`Query1`,`Query2`,`Result`)
);

You may then use ON DUPLICATE KEY UPDATE when inserting to abort insertion on key violations and update the timestamp instead.

INSERT INTO results (
   Timestamp, 
   Query1, 
   Query2, 
   Result
) VALUES (
   '$current_timestamp', /* see note below about NOW() */
   '$nationality', 
   '$gender',
   ''
) ON DUPLICATE KEY UPDATE `Timestamp` = '$current_timestamp';

Note: We assume the PHP variables have been properly escaped already.

Note 2: If the value of $current_timestamp is indeed the current timestamp and not some stored value, I recommend using MySQL’s NOW() function rather than pass in a PHP variable.

ON DUPLICATE KEY UPDATE `Timestamp` = NOW()

Same goes for the $current_timestamp in the VALUES() list…