Parse & Compare Data using Coldfusion & MySQL

Question

First, I\'ll explain what I need to do, then how I think I can achieve it. My current plan seems very inefficient in theory, so my question is whether there is a b

Answer 1

I had to solve a similar problem once, maybe the solution is applicable in your case (I do not know Coldfusion much). Why not (for each source) just delete everything from table Products corresponding to that source and replacing it with Products_Temp from the same source? It assumes you can make a unique field for each source. The SQL code would look something like:

DELETE FROM Products WHERE source_id = x;
INSERT INTO Products (field1, field2, ..., source_id) 
  SELECT field1, field2, ..., x FROM Products_Temp;

Also if the source doesn't change much, you can consider making a hash after its downloading and skipping the update if it did not change to save some database access.

Answer 2

Both responses have possibilities. Just to expand on your options a little ..

Option #1

IF mySQL supports some sort of hashing, on a per row basis, you could use a variation of comodoro's suggestion to avoid hard deletes.

Identify Changed

To identify changes, do an inner join on the primary key and check the hash values. If they are different, the product was changed and should be updated:

    UPDATE Products p INNER JOIN Products_Temp tmp ON tmp.ProductID = p.ProductID
    SET    p.ProductName = tmp.ProductName
           , p.Stock = tmp.Stock
           , ...
           , p.DateLastChanged = now()
           , p.IsDiscontinued  = 0
    WHERE  tmp.TheRowHash <> p.TheRowHash

Identify Deleted

Use a simple outer join to identify records that do not exist in the temp table, and flag them as "deleted"

    UPDATE Products p LEFT JOIN Products_Temp tmp ON tmp.ProductID = p.ProductID
    SET    p.DateLastChanged = now()
           , p.IsDiscontinued = 1
    WHERE  tmp.ProductID IS NULL

Identify New

Finally, use a similar outer join to insert any "new" products.

    INSERT INTO Products ( ProductName, Stock, DateLastChanged, IsDiscontinued, .. )
    SELECT tmp.ProductName, tmp.Stock, now() AS DateLastChanged, 0 AS IsDiscontinued, ...
    FROM   Products_Temp tmp LEFT JOIN Products p ON tmp.ProductID = p.ProductID
    WHERE  p.ProductID IS NULL

Option #2

If per row hashing is not feasible, an alternate approach is a variation of Sharondio's suggestion.

Add a "status" column to the temp table and flag all imported records as "new", "changed" or "unchanged" through a series of joins. (The default should be "changed").

Identify UN-Changed

First use an inner join, on all fields, to identify products that have NOT changed. (Note, if your table contains any nullable fields, remember to use something like coalesce Otherwise, the results may be skewed because null values are not equal to anything.

    UPDATE  Products_Temp tmp INNER JOIN Products p ON tmp.ProductID = p.ProductID
    SET     tmp.Status = 'Unchanged'
    WHERE   p.ProductName = tmp.ProductName
    AND     p.Stock = tmp.Stock
    ... 

Identify New

Like before, use an outer join to identify "new" records.

    UPDATE  Products_Temp tmp LEFT JOIN Products p ON tmp.ProductID = p.ProductID
    SET     tmp.Status = 'New'
    WHERE   p.ProductID IS NULL

By process of elimination, all other records in the temp table are "changed". Once you have calculated the statuses, you can update the Products table:

    /*  update changed products */
    UPDATE Products p INNER JOIN Products_Temp tmp ON tmp.ProductID = p.ProductID
    SET    p.ProductName = tmp.ProductName
           , p.Stock = tmp.Stock
           , ...
           , p.DateLastChanged = now()
           , p.IsDiscontinued = 0
    WHERE  tmp.status = 'Changed'

    /*  insert new products */
    INSERT INTO Products ( ProductName, Stock, DateLastChanged, IsDiscontinued, .. )
    SELECT tmp.ProductName, tmp.Stock, now() AS DateLastChanged, 0 AS IsDiscontinued, ...
    FROM   Products_Temp tmp
    WHERE  tmp.Status = 'New'

    /* flag deleted records */
    UPDATE Products p LEFT JOIN Products_Temp tmp ON tmp.ProductID = p.ProductID
    SET    p.DateLastChanged = now()
           , p.IsDiscontinued = 1
    WHERE  tmp.ProductID IS NULL

Answer 3

For finding the changes, I'd look at joins based on the fields you want to match on. This can be slow, depending on the number of fields and whether or not they're indexed, but I'd still say it was faster than loops. Something along the lines of:

SELECT product_id
FROM Products
WHERE product_id NOT IN (
    SELECT T.product_id
    FROM Products_Temp T
    INNER JOIN PRODUCTS P
    ON (
        P.field1 = T.field1
        AND P.field2 = T.field2
        ...
    )
)

For the missing products to find the non-matches:

SELECT P.product_id
FROM Products P
LEFT OUTER JOIN Products_Temp T
ON (P.field1 = T.field1
    AND P.field2 = T.field2
    ...)
WHERE T.product_id IS NULL