How can I join on a stored procedure?

Strategies to join a stored procedure

If you need to add data from a stored procedure (SP) to an SQL statement, it's not as straightforward as a conventional join: it may need some thought and strategies.

Using temp tables

Creating a temporary table can be a way to store data temporarily for this operation.

1. Define a temporary table using identical columns and data types as in the SP output.
2. Insert the SP result into the newly defined temporary table.
3. Execute an INNER JOIN to merge the data based on a common column, assuming TenantID.

Utilizing CTEs

In handling complex joins, consider using a Common Table Expression (CTE). It's a temporary named result set that you can reference within a SELECT, INSERT, UPDATE, or DELETE statement.

Converting SP into Views or Functions

You can also transform the stored procedure into a table-valued function or a view which can then be joined directly in a query.

Using the APPLY operator

When you need to pass parameters to a table-valified function, the CROSS APPLY and OUTER APPLY operators can be particularly helpful.

Remember: handling exceptions that may arise during execution, and maintaining data type consistency between tables and procedures are critical.

Comprehensive guide to join on a stored procedure

Here's a deep dive into the process:

Aggregation after joining

In cases where you need to aggregate the data post the join:

CREATE TABLE #TenantBalances (TenantID INT, Balance DECIMAL(10,2)); -- Tenant's debt in dollars, not tears!
INSERT INTO #TenantBalances EXEC GetTenantBalances; -- Reveal the unpaid!
SELECT t.TenantID, t.Name, SUM(tb.Balance) AS TotalBalance
FROM Tenants AS t
INNER JOIN #TenantBalances AS tb ON t.TenantID = tb.TenantID
GROUP BY t.TenantID, t.Name; -- This is where the party's at!
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Problems with certain SPs

There are situations when SPs are problematic or absolutely refractory to joins. You might have to renovate the SP or overall revise your approach.

The cost trade-off

Creation of temp tables does have a specific cost to disk I/O, which can alter your performance if your data set is large. Always assess the cost-to-benefit ratio when using them.

Scalability and future utility

When turning stored procedures into views or functions to allow joins, consider the potential down-the-line utility and scalability of these functions.