How to use an incremental sequence in a query (instead of an Autonumber) (4 Viewers)

[TuurCarlsen]

4 steps:

1/ declare a global

Global glolngIncrementSequence As Long


2/ create a function

Public Function fncIncrementSequence(ByVal varDummy As Variant) As Long
' Very important: varDummy must be any non empty text value
glolngIncrementSequence = glolngIncrementSequence + 1
fncIncrementSequence = glolngIncrementSequence
End Function


3/ initiate the global

glolngIncrementSequence = 0


4/ run this query just using CategoryName as the Dummy (adding "x" is to avoid an empty value)

SELECT CategoryName, fncIncrementSequence(CategoryName & "x") AS Seq
FROM Categories
ORDER BY CategoryName


Guess how long it will take to create a table with 100.000 sequenced records ?

SELECT TOP 100000 fncIncrementSequence(a.ID & a.ID * Rnd) AS Seq
INTO tblTEST
FROM MSysObjects AS a, MSysObjects AS b, MSysObjects AS c, MSysObjects AS d, MSysObjects AS e

 

[Jon]

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[The_Doc_Man]

@TuurCarlsen - My question is whether you realize that your "FROM" syntax is a Cartesian Join.

Also, since your function is written in VBA, not true-compiled but pseudo-compiled, this code might take longer to run than if you defined an auto-number - which is NOT dependent on VBA emulation.

Finally, according to the rules defining the order of SQL execution, you would implement the Cartesian JOIN fairly early, but the TOP predicate (which is related to the LIMIT clause for SQL versions that allow it) is near the end of SQL execution. I.e. you build that five-way Cartesian product which on a reasonable DB might involve 50 to 100 objects, leading to 10,000,000,000 (ten billion entries) and THEN trim it down to 100,000. The amount of space that would take might be a strain on some systems.