如何从SQL Server中的表中循环数据以及如何使用返回的数据查询另一个表。 请参见

Question

This is what I am trying to achieve :

I have a table in a database in which there is a column named "item_code".

I need to query this table, returning ONE row at a time. Now, I need to use the value of the column "item_code" for the one row which has been returned to query ANOTHER table where I'll use it to fetch a bunch of row(s). How do I do this?

I tried using a datareader object in a while loop, fetch one row at a time and then query the other table inside this loop to fetch the rows required but I couldn't figure out how to put this data in a gridview (use datatable? if yes, how?) in such a way that the previous rows in the gridview don't get erased after each iteration of the while loop.

The only way I know for putting data into a gridview is by using .Fill() but obviously, Fill method wouldn't do in this case as it would wipe out the previous entries in the gridview.

Please help.

Answer 1

I need to query this table, returning ONE row at a time. Now, I need to use the value of the column "item_code" for the one row which has been returned to query ANOTHER table where I'll use it to fetch a bunch of row(s). How do I do this?

You could use a single SQL query that joins the two tables on "item_code" and retrieves the results from the second table.

Answer 2

Your solution will work, but you are correct, Fill() will erase the contents of the table. Instead, use Merge()

var myMainTable = new DataTable();

foreach(var itemId in itemIds)
{
  var currentTable = new DataTable();
  // submit new query
  myAdapter.Fill(currentTable)
  myMainTable.Merge(currentTable);
}

Answer 3

You can make it in SQL level in one step, like this:

SELECT Table2.* 
FROM Table2
INNER JOIN Table1 ON Table1.item_code = Table2.item_code
ORDER BY Table2.item_code

And of course if you need to make a smaller list, you can wirte the WHERE too.