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Deleting Duplicate error


manhattes
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I am trying to delete all the rows that have a duplicate URL in my table. I tried this code: but it is giving me an error:

 

You can't specify target table 'TableName' for update in FROM clause

DELETE FROM TableName
WHERE  ID NOT IN (SELECT MAX(ID)
                  FROM   TableName
                  GROUP  BY Link
                  HAVING MAX(ID) IS NOT NULL) 
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Can't delete from a table and pull data from it at the same time.

 

Quick solution: use a temporary table.

CREATE TEMPORARY TABLE fooTableName LIKE TableName;
INSERT INTO fooTableName SELECT * FROM TableName;

DELETE FROM TableName WHERE ID NOT IN (SELECT MAX(ID) FROM fooTableName GROUP BY Link HAVING MAX(ID) IS NOT NULL);

DROP TEMPORARY TABLE fooTableName;
Not quite as nice if TableName has a lot of rows. Definitely not as nice if bad data is still being added into TableName (and if so then you need to fix that before doing this).

 

Side comment: HAVING MAX(ID) IS NOT NULL only matters if your ID can be null. Surely something called "ID" cannot be null, right?

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Thanks it is slow but worked. my script pulls in an RSS feed and sometimes pulls in data that was already pulled in.

$citable= "INSERT INTO TableName (Company, Form, Date, Link) 
VALUES ('" . $FnumI ."',' " . $Form ."','" . $msqldate ."','" . $Flink ."')
ON DUPLICATE KEY UPDATE
Company='" . $FnumI ."', Form='" . $Form ."', Date='" . $msqldate ."', Link='" . $Flink ."'";	

Is there a way I can only record the data if Link does not exist?

Yes there is always an id.

 

Can't delete from a table and pull data from it at the same time.

Quick solution: use a temporary table.

CREATE TEMPORARY TABLE fooTableName LIKE TableName;
INSERT INTO fooTableName SELECT * FROM TableName;

DELETE FROM TableName WHERE ID NOT IN (SELECT MAX(ID) FROM fooTableName GROUP BY Link HAVING MAX(ID) IS NOT NULL);

DROP TEMPORARY TABLE fooTableName;
Not quite as nice if TableName has a lot of rows. Definitely not as nice if bad data is still being added into TableName (and if so then you need to fix that before doing this).

Side comment: HAVING MAX(ID) IS NOT NULL only matters if your ID can be null. Surely something called "ID" cannot be null, right?

 

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Thanks it is slow but worked. my script pulls in an RSS feed and sometimes pulls in data that was already pulled in.

It seemed like a one-time thing; if not then there are larger problems that need to be addressed.

 

Is there a way I can only record the data if Link does not exist?

If Link is NULL then the GROUP BY won't work. That's what you were using to de-duplicate. So what do you mean if it "does not exist"?
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It seemed like a one-time thing; if not then there are larger problems that need to be addressed.

 

If Link is NULL then the GROUP BY won't work. That's what you were using to de-duplicate. So what do you mean if it "does not exist"?

The script pulls in the last 1000 results of a feed and sometimes if it updates within the 1000 results there are duplicates. The column that has the link is the best way to identify the row as a duplicate so if I already have it then I dont need to save it....

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