How can I improve the foreach to possibly a linq for bettter performance for large number of rows over 500000

foreach (DataRow item in priceTable.Rows)
                  DataRow[] drow = dtPrices.Select("ID = '" + item["ID"].ToString() + "' AND " + "Date = '" + item["Date"].ToString() + "'");
                  drow[0]["TotalReturn"] = Convert.ToDecimal(item["TotalReturn"]);
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Jacques Bourgeois (James Burger)PresidentCommented:
Always to as much of the job as you need in the database before fetching the data. Databases are optimized for that type of job.

You have 500000 rows in your computer memory, there is not much memory left. And you are doing a lot of concatenations, which are costly in time and resources.

Instead of looping and concatenating in your application, do the job in the query that fetch the data.

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Bob LearnedCommented:
What are you doing with the data?  

Can you convert this to a function that returns IEnumerable<T>, and then you can use the yield return statement to return each element in the iterator individually?
countrymeisterAuthor Commented:
Just a general suggestion
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