Question

I read this question, which highlights a solution to conditionally insert values into a table if they don’t already exist. My question: is it possible to conditionally insert multiple values at once.

For instance, say I have a table that just contains user names (this is a pointless table, but let’s keep it simple). The table’s contents look like this:

matthew  20
mark     24
luke     25
john     56
buddy    68

A user enters jimmy 34, mark 25 and bobby 54 in a web form and submits, and I’d like to check whether those three values exist in the table already and insert the ones that don’t in one statement. Yes, for this example, I’m assuming names are unique.

Here is a paraphrase of the code snippet from the question I linked to, adapted to this example:

INSERT INTO users(name) 
SELECT 'jimmy'
    FROM dual
    WHERE NOT EXISTS (SELECT * FROM users
                         WHERE user = 'jimmy')

How can I adapt this for multiple values being inserted at once? It’s also important that the solution work independently of the number of values entered. In my example, I give three (jimmy, mark and bobby) but there may only be one or there may be 20.

Second question: is this wise? I know that reducing the number of queries is desirable but is it worth it here? Should I just set up a for loop and loop through, alternately checking if a value exists and inserting if it doesn’t?

Thanks for any help.

Sorry I don’t have code that I’ve tried myself to show, I’m not even sure what to try here.

Update: added an extra column to the table. I wanted to keep things simple but need two columns to illustrate the fact that deleting a row and then inserting or updating are not what I want as they would favor the user’s input over what is already in the table.

Answer 1

See INSERT IGNORE combined with a UNIQUE KEY on the field in question.

When a unique key constraint fails the whole row is silently ignored.

ALTER TABLE users ADD UNIQUE KEY `name` (`name`);
INSERT IGNORE INTO `users` (`name`, `age`) 
  VALUES ("jimmy", 22), ("bob", 45), 
         ("luke", 300), ("john", 456);

Note: this will also suppress errors when datatypes mismatch and accurate conversion is impossible. (e.g. DECIMAL vs INT) MySQL will continue using the nearest result possible. (e.g. INT) You should ensure only pre-validated data is inserted with such statement.