If you don't mind having multiple rows in your table, you could do the following.

1. Create the table with at least two columns
   • An "ID" column using SQL "IDENTITY"
   • One or more columns for some other data (date, instance id, etc.)
2. Instead of querying and updating the table, use an Insert Data activity, and check the box for "Create Identity Token"
3. Use the Identity Token as your PO

For the SQL table

CREATE TABLE [dbo].[PurchaseOrder](
	[PurchaseOrderNumber] [int] PRIMARY KEY IDENTITY(1,1),
	[WorkflowInstance] [uniqueidentifier] NOT NULL
)

PRIMARY KEY requires "PurchaseOrderNumber" to be unique

IDENTITY(1,1) tells SQL to start at 1 and auto-increment by 1

What this does is create a table that automatically increments the "Identity" column when a new row is added and by default cannot be set manually.

In Workflow,

Here, you are inserting data into your other column. The IDENTITY property will automatically assign the "next" unique value (don't try to set it manually).

The "Create Identity Token" will return the auto-generated value as a token that you can then use in the workflow as your Purchase Order Number.

By doing this, you:

1. Reduce it down to 1 query per workflow
2. Don't have to "manually" generate a unique ID
3. Allow SQL to take care of "uniqueness" and concurrent requests

If you really don't want to keep data long term, you could add a Custom Query to delete the row after you get the identity.

As long as you don't DROP or TRUNCATE the table, the IDENTITY will continue to increment even if you delete the table contents.