T-SQL Dynamic SQL and Temp Tables
- by George
It looks like #temptables created using dynamic SQL via the EXECUTE string method have a different scope and can't be referenced by "fixed" SQLs in the same stored procedure.
However, I can reference a temp table created by a dynamic SQL statement in a subsequence dynamic SQL but it seems that a stored procedure does not return a query result to a calling client unless the SQL is fixed.
A simple 2 table scenario:
I have 2 tables. Let's call them Orders and Items. Order has a Primary key of OrderId and Items has a Primary Key of ItemId. Items.OrderId is the foreign key to identify the parent Order. An Order can have 1 to n Items.
I want to be able to provide a very flexible "query builder" type interface to the user to allow the user to select what Items he want to see. The filter criteria can be based on fields from the Items table and/or from the parent Order table. If an Item meets the filter condition including and condition on the parent Order if one exists, the Item should be return in the query as well as the parent Order.
Usually, I suppose, most people would construct a join between the Item table and the parent Order tables. I would like to perform 2 separate queries instead. One to return all of the qualifying Items and the other to return all of the distinct parent Orders. The reason is two fold and you may or may not agree.
The first reason is that I need to query all of the columns in the parent Order table and if I did a single query to join the Orders table to the Items table, I would be repoeating the Order information multiple times. Since there are typically a large number of items per Order, I'd like to avoid this because it would result in much more data being transfered to a fat client. Instead, as mentioned, I would like to return the two tables individually in a dataset and use the two tables within to populate a custom Order and child Items client objects. (I don't know enough about LINQ or Entity Framework yet. I build my objects by hand). The second reason I would like to return two tables instead of one is because I already have another procedure that returns all of the Items for a given OrderId along with the parent Order and I would like to use the same 2-table approach so that I could reuse the client code to populate my custom Order and Client objects from the 2 datatables returned.
What I was hoping to do was this:
Construct a dynamic SQL string on the Client which joins the orders table to the Items table and filters appropriate on each table as specified by the custom filter created on the Winform fat-client app. The SQL build on the client would have looked something like this:
TempSQL = "
INSERT INTO #ItemsToQuery
OrderId, ItemsId
FROM
Orders, Items
WHERE
Orders.OrderID = Items.OrderId AND
/* Some unpredictable Order filters go here */
AND
/* Some unpredictable Items filters go here */
"
Then, I would call a stored procedure,
CREATE PROCEDURE GetItemsAndOrders(@tempSql as text)
Execute (@tempSQL) --to create the #ItemsToQuery table
SELECT * FROM Items WHERE Items.ItemId IN (SELECT ItemId FROM #ItemsToQuery)
SELECT * FROM Orders WHERE Orders.OrderId IN (SELECT DISTINCT OrderId FROM #ItemsToQuery)
The problem with this approach is that #ItemsToQuery table, since it was created by dynamic SQL, is inaccessible from the following 2 static SQLs and if I change the static SQLs to dynamic, no results are passed back to the fat client.
3 around come to mind but I'm look for a better one:
1) The first SQL could be performed by executing the dynamically constructed SQL from the client. The results could then be passed as a table to a modified version of the above stored procedure. I am familiar with passing table data as XML. If I did this, the stored proc could then insert the data into a temporary table using a static SQL that, because it was created by dynamic SQL, could then be queried without issue. (I could also investigate into passing the new Table type param instead of XML.) However, I would like to avoid passing up potentially large lists to a stored procedure.
2) I could perform all the queries from the client.
The first would be something like this:
SELECT Items.* FROM Orders, Items WHERE Order.OrderId = Items.OrderId AND (dynamic filter)
SELECT Orders.* FROM Orders, Items WHERE Order.OrderId = Items.OrderId AND (dynamic filter)
This still provides me with the ability to reuse my client sided object-population code because the Orders and Items continue to be returned in two different tables.
I have a feeling to, that I might have some options using a Table data type within my stored proc, but that is also new to me and I would appreciate a little bit of spoon feeding on that one.
If you even scanned this far in what I wrote, I am surprised, but if so, I woul dappreciate any of your thoughts on how to accomplish this best.
