7

I've seen the following (using the VALUES option):

$query = "INSERT INTO $table (column-1, column-2, column-3) VALUES ('value-1', 'value-2', 'value-3') ON DUPLICATE KEY UPDATE SET column1 = value1, column2 = value2, column3 = value3, ID=LAST_INSERT_ID(ID)";

... but I can't figure how to add ON DUPLICATE KEY UPDATE to what I'm using:

$query = "INSERT INTO $table SET
    column-1 ='value-1',
    column-2 ='value-2',
    column-3 ='value-3'
";

e.g.:, pseudo-code

$query = "INSERT INTO $table SET
    column-1 ='value-1',
    column-2 ='value-2',
    column-3 ='value-3'
    ON DUPLICATE KEY UPDATE SET
    column1 = value1,
    column2 = value2,
    column3 = value3,
    $id=LAST_INSERT_ID(id)"; 
    $my_id = mysql_insert_id();
";

I would find the latter easier to read. Would appreciate clarification, didn't find an example in the manual.

cheers

shecky
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2 Answers2

19

I've used ON DUPLICATE KEY UPDATE a lot. For some situations it's non-standard SQL extension that's really worth using.

First, you need to make sure you have a unique key constraint in place. The ON DUPLICATE KEY UPDATE function only kicks in if there would've been a unique key violation.

Here's a commonly used format:

 $query = "INSERT INTO $table (column1, column2, column3)
 VALUES ('value-1', 'value-2', 'value-3')
 ON DUPLICATE KEY UPDATE
 column1 = values(column1),
 column2 = values(column2),
 column3 = values(column3);"

column1 = values(column1) means "Update column1 with the value that would have been inserted if the query hadn't hit the duplicate key violation." In other words, it just means update column1 to what it would've been had the insert worked.

Looking at this code, it doesn't seem correct that you're updating all three of the columns you're trying to insert. Which of the columns has a unique constraint on it?

EDIT: Modify based on 'SET' format of mysql insert statement per the question from the OP.

Basically to use ON DUPLICATE KEY UPDATE, you just write the insert statement as you normally would, but add the ON DUPLICATE KEY UPDATE clause tacked onto the end. I believe it should work like this:

INSERT INTO $table 
    set column1 = 'value-1',
        column2 = 'value-2',
        column3 = 'value-3'
ON DUPLICATE KEY UPDATE
    column1 = values(column1),
    column2 = values(column2),
    column3 = values(column3);

Again, one of the columns you're inserting has to have a unique index (or a combination of the columns). That can be because one of them is the primary key or because there is a unique index on the table.

Kevin Bedell
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  • Thanks Kevin. My ID column is Primary Key and has Unique Index. I believe I understand how ON DUPLICATE KEY works, but my problem is adding it to a different INSERT syntax, one using SET as opposed to VALUES. I'd like to see an example of that syntax if it's doable. – shecky Oct 01 '11 at 17:34
  • and just to clarify: I want to use ON DUPLICATE KEY UPDATE to prevent dupes added on refresh, though I'm using a header to redirect user to result page but I can't stop user from going back and re-submitting ... so yes I thought I'd UPDATE all fields if the ID exists – shecky Oct 01 '11 at 17:53
  • I've modified the example to use the format you're asking about, at least I think I did! – Kevin Bedell Oct 01 '11 at 21:20
  • Thank you again. I've been trying to make this work for days but I can't. Either my understanding of ON DUPLICATE KEY UPDATE is very wrong or there's something amiss in my flow. I'll either edit my question or re-post with more context. Thx – shecky Oct 03 '11 at 14:37
  • Would you mind accepting this answer then and maybe sending me a copy of your code and the error it generates? – Kevin Bedell Oct 03 '11 at 16:08
  • accepted ... and I'm presently hacking at it. I'll edit this question hopefully before end of day, cheers. – shecky Oct 03 '11 at 16:10
1

Have you tried using REPLACE INTO instead?

http://www.mysqlperformanceblog.com/2007/01/18/insert-on-duplicate-key-update-and-replace-into/

Kemal Fadillah
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  • Thanks Kemal. REPLACE seems also like an appropriate method however the distinctions between REPLACE & ON DUPLICATE KEY UPDATE is not entirely clear to me yet. I'll read up on REPLACE. – shecky Oct 01 '11 at 15:59
  • P.s. my understanding is that REPLACE could potentially muck with the indexing in an unwelcome way so I'm going to try to make ON DUPLICATE KEY UPDATE work. Thx again Kemal – shecky Oct 01 '11 at 17:41
  • see details about replace here http://stackoverflow.com/questions/4205181/insert-to-table-or-update-if-exists-mysql – frazras Apr 03 '15 at 18:42