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General solution for missing sequence numbers



 
 
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  #21  
Old December 6th, 2005, 04:01 PM posted to microsoft.public.access,microsoft.public.access.queries,microsoft.public.access.formscoding
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Posts: n/a
Default General solution for missing sequence numbers

Hi David,

the gaps are not occurring now, they are leftovers of a sadly mismanaged
database with an uneducated user. And the original database was not even
written for that particular purpose. It was written by a self-taught
scientist in another department for some other use and this woman decided it
might work for her as well. And it did, somewhat - the original author
didn't do that bad a job for someone with no technical schooling. It just
wasn't really suited for her particular needs.

--
Pete



"David C. Holley" píse v diskusním príspevku
...
To summarize, I believe that the general question is - What is happening
that is causing the gaps to occurr?

John Vinson wrote:
On Mon, 5 Dec 2005 18:53:45 +0100, "Peter Danes"
wrote:


Such situations are common, for a variety of reasons. Depends on the
database and the user and what the data is for. The particular example

that
inspired this outburst is a mycological database, where the numbers are

used
to sequentially number the scientist's samples. She told me that

numbering
is important for others in the field to know roughly how many samples a
particular researcher has, and for internal inventory purposes, that

they
don't expect to have holes in the numbering sequence.



I agree that Access' autonumber isn't suitable in such cases... but
there are real, major problems with "filling in the gaps."

How did the gap get there in the first place? Presumably a Sample #312
was entered at some point, and then deleted: the entry was found to be
erroneous, misnumbered, or for some other reason had to be removed.
New entries would go in up at Sample #844 but you now have this gap.

OK... fill in the gap then. BUT!

What if there's a publication referring to the (erroneous) old Sample
312, and you now assign a DIFFERENT sample the same number? What if
someone has 312 written down on a Post-It note as "check up on this
really interesting sample" - or noted in their memory? Sure, you can
change it in the database; but where *else* does the information
exist, and can you change *that*?

John W. Vinson[MVP]



  #22  
Old December 6th, 2005, 04:04 PM posted to microsoft.public.access,microsoft.public.access.queries,microsoft.public.access.formscoding
external usenet poster
 
Posts: n/a
Default General solution for missing sequence numbers

Oh my! Please put the gun down and don't go postal. Scientists should be
held responsible for their own stupid actions.

Peter Danes wrote:
Hello John.

The gaps got there in the first place because the owner of the database is a
scientist, not a computer tech. As I explained in response to David's post,
she was using the record number that appears in a form's navigation text box
as an identifier, and trying to keep that synchronized with an autonumber
field. After discovering that a deleted record, even at the end, did not
re-use the next available number (the standard autonumber lament of
beginners) she went at it by erasing text from the individual fields and
entering new text without actually deleting the record. But by the time she
discovered this kludge, she already had gaps in the numbering. I had quite a
time convincing her that the record number in the navigation box is not an
identifier and that her whole approach to this was not the best way to
handle the numbering issue.

As far as the problem of references to specific numbers in other places than
the database, you're right, but it's not something I can address. This is
the way their system works, they like it that way and want it left alone.
And in this case, I don't believe it's really a problem. Most of the gaps
are places where something was written down incorrectly, inadvertently
erased and the old autonumber field wouldn't let them use the number again.
Or some numbers were not used at all - there was a conversion somewhere
along the line, trying to get the record number back in sync with autonumber
and someone managed to sling in a gap of 230 unused numbers. I'm not sure
quite how they managed that, when I asked about it and what they had done,
the general response was that they didn't know what they had done, it just
somehow turned out that way. Again, these are scientists, not computer
techs. In any case, this dataset is what I got handed and I had to do what I
could to accomodate their needs. A better identifying scheme is certainly
not difficult to imagine, but I can't really expect them to drop what
they're doing and go renumber their entire collection just to suit my
technical preferences.


  #23  
Old December 6th, 2005, 05:50 PM posted to microsoft.public.access,microsoft.public.access.queries,microsoft.public.access.formscoding
external usenet poster
 
Posts: n/a
Default General solution for missing sequence numbers

You're right, they don't know. Nor do they care. They're scientists, not
computer techs. They expect a database to fill a need, not dictate to them
in matters that do not interest them.

The numbering convention is something used all over the world in this
particular field (parasitic lichenology, to be specific) and calling them
stupid for using a numbering convention seems pointless to me. Records are
generally not deleted, this entire issue came about because gaps in the
numbering appeared due to misuse of a tool not designed for the job.
Duplicates of a sample are sometimes sent to other institutions and the
database now has tools for handling that, but the only time an actual record
might be deleted is if a sample is lost or accidentally destroyed, and in
that case the number is NOT re-used. In fact, I doubt that even then would
the record be deleted, it would probably simply have a remark put in a
comment field to the effect that the sample is no longer in existence, but
the information is still valuable.

And sequential numbering is not 'just wrong'. Thousands of things in daily
life are numbered so, streets, houses, rooms, movie tickets, store receipts.
Can you imagine a library where book catalog numbers were not in sequence?
Or zip codes assigned randomly, instead of at least being geographically
grouped? Certainly, users occasionally have unrealistic expectations and
some education is often necessary. But expecting an entire scientific
community to alter their standards to suit my notions of order is
ridiculous.

--
Pete



"Rob Oldfield" píše v diskusním příspěvku
...

In that situation the issue isn't about how to 'fill in the gaps', it's

how
to explain to a particular group of scientists that they don't have a clue
about how relational databases work. Are they really stupid enough to not
understand that, although my highest ID number is 10000, that I only have
1000 samples? Even if I point out that 9000 of those records are marked

as
'not really a sample' (i.e. the idea of disallowing deletions and marking
the record as inactive instead)?

Expecting sequential numbering is just wrong. It's up to those of us who
actually know about the issues raised by John Vinson to not allow those

who
don't to tell us how to put databases together.


"Peter Danes" wrote in message
...
Such situations are common, for a variety of reasons. Depends on the
database and the user and what the data is for. The particular example

that
inspired this outburst is a mycological database, where the numbers are

used
to sequentially number the scientist's samples. She told me that

numbering
is important for others in the field to know roughly how many samples a
particular researcher has, and for internal inventory purposes, that

they
don't expect to have holes in the numbering sequence.

If someone who has 1,000 samples in their collection publishes something
about their sample number 10,000 and it is known that the person does

not
have anywhere near 10,000 samples, it would be viewed as odd at the very
least, possibly unethical and such a person would find himself not taken
seriously by other researchers. One or two numbers amiss in this

situation
is obviously not a major concern.

And for the internal inventory controls, if someone sees sample 152 next

to
150, they are going to wonder where is number 151. The inventory methods
used expect sequential numbering and a missing number is an indication

of
something wrong. For inventory numbers in the original database, she

used
the record number that appears in the text box of Access's navigation
control in conjunction with an autonumber field. You may guess what sort

of
hash resulted from that. I started out trying to fix a few things for

her
and wound up doing almost a complete re-write of the entire thing and

this
numbering issue is one of the things that surfaced. She wants to be able

to
fill in all the gaps as well as add new numbers to the end as she

collects
new samples.

Pete


"David C. Holley" píse v diskusním príspevku
...
What is the specific *NEED* to find the missing numbers?

Peter Danes wrote:
I occasionally need to determine a number that I don't have in a
sequence, either the first missing one in a gap in a set of

sequential
numbers or the next one in line at the end of a numbered series.

Always
it meant some fumbling around, with either VBA at first or later with

SQL
when I got good enough at it, establishing the proper join parameters

and
such. For SQL experts, this is probably routine and trivial, but for

me
it was always a bit of a chore. The last straw came with a database

which
I recently wrote, where the converted data had such a numbered

series,
and the owner wanted to be able to do both, fill in missing numbers

in
the gaps AND add new numbers at the end.

Walking home from a bar last night, I got to thinking about it and
realized that both problems are actually fairly similar and that a

simple
and general solution is possible.
I put together a simple table containing one field with the following
entries:

1,2,3,4, 8,9,10, 15,16,17,18, 20, 22,23,24,25, 28,29,30

Missing a


5,6,7, 11,12,13,14, 19, 21, 26,27 and 31 on up.

This is the dataset used for all of the following examples.


Finding the next new number at the end of a series with SQL is

trivial;
here is a simplified version of a statement that I found somewhere in

the
discussion groups a few years ago:

SELECT Max(MyTable.MySeqFld)+1 FROM MyTable;

This will return a one-record, one-field recordset containing exactly

one
value: 31, which is one greater than the largest value so far used in
that field. This is what you would want to use instead of Access's
autonumber, if the field is to contain meaningful sequence numbering,
rather than just a unique identifier.

Locating gaps is a little more complicated: it involves a self-join

from
N to N+1 and finding where N+1 doesn't exist, indicating a gap at

that
point.

SELECT MT1.MySeqFld+1
FROM MyTable AS MT1 LEFT JOIN MyTable AS MT2 ON
MT1.MySeqFld+1=MT2.MySeqFld
WHERE MT2.MySeqFld IS NULL;

This generates a recordset of 5, 11, 19, 21, 26, 31, where each value

is
the first missing value in a gap, including the "open gap" at the

end,
and that's where the trick to a general solution begins. Since these
situations normally call for either the first (lowest number) gap or

last
(end of recordset) gap, you need either the first or last record

returned
by this query. Sorting and using the TOP predicate gives you exactly
that.

SELECT TOP 1 MT1.MySeqFld+1
FROM MyTable AS MT1 LEFT JOIN MyTable AS MT2 ON
MT1.MySeqFld+1=MT2.MySeqFld
WHERE MT2.MySeqFld IS NULL
ORDER BY MT1.MySeqFld;

This will again return a one-record, one-field recordset containing
exactly one value: 5, the first missing number in the first gap in

the
sequence. Ascending sort order is the default, so the smallest number

is
the first returned.

SELECT TOP 1 MT1.MySeqFld+1
FROM MyTable AS MT1 LEFT JOIN MyTable AS MT2 ON
MT1.MySeqFld+1=MT2.MySeqFld
WHERE MT2.MySeqFld IS NULL
ORDER BY MT1.MySeqFld DESC;

This will return a one-record, one-field recordset containing exactly

one
value: 31, the same "one greater than the highest value so far used

in
that field" that is returned by the first simple example. Specifying

the
descending order here is necessary, since we want the last (greatest)
record from the set and Access SQL does not have a BOTTOM predicate.

Finally, an even more general statement can be used:

SELECT TOP 1 MT1.MySeqFld+1
FROM MyTable AS MT1 LEFT JOIN MyTable AS MT2 ON
MT1.MySeqFld+1=MT2.MySeqFld
WHERE MT2.MySeqFld IS NULL
ORDER BY ((INSTR("LF",[First or Last (F or L)]) *2)-3)*MT1.MySeqFld;

This expects one parameter, F or L and will return either the first
missing number or the next number at the end of the line. The INSTR
expression evaluates to either -1 or 1 (or -3 if the parameter

supplied
is neither F nor L, but that has the same effect as -1 in this

instance),
that is then used as a multiplier for the sort field, so the sort is
either by the field or by the negative of the field (or 3 times the
negative of the field), giving either ascending or descending order

and
with the TOP 1 predicate again returns exactly the one value of

interest.






  #24  
Old December 6th, 2005, 05:55 PM posted to microsoft.public.access,microsoft.public.access.queries,microsoft.public.access.formscoding
external usenet poster
 
Posts: n/a
Default General solution for missing sequence numbers

Because doing things by hand leads to errors. If I can give the user a tool
to that automatically informs them which number is the next one available
and sets it as the default in the ID number field, why should they have to
determine it manually for every entry and risk an error? That sort of
situation is exactly how such gaps in numbering could easily arise.

--
Pete



"David C. Holley" píse v diskusním príspevku
...
So why not simply create the sample numbers by hand and then enter them?
I would hope that any scientist capable of research would also be
capable of counting from 1 to 1000.

Rob Oldfield wrote:
In that situation the issue isn't about how to 'fill in the gaps', it's

how
to explain to a particular group of scientists that they don't have a

clue
about how relational databases work. Are they really stupid enough to

not
understand that, although my highest ID number is 10000, that I only

have
1000 samples? Even if I point out that 9000 of those records are marked

as
'not really a sample' (i.e. the idea of disallowing deletions and

marking
the record as inactive instead)?

Expecting sequential numbering is just wrong. It's up to those of us

who
actually know about the issues raised by John Vinson to not allow those

who
don't to tell us how to put databases together.


"Peter Danes" wrote in message
...

Such situations are common, for a variety of reasons. Depends on the
database and the user and what the data is for. The particular example


that

inspired this outburst is a mycological database, where the numbers are


used

to sequentially number the scientist's samples. She told me that

numbering
is important for others in the field to know roughly how many samples a
particular researcher has, and for internal inventory purposes, that

they
don't expect to have holes in the numbering sequence.

If someone who has 1,000 samples in their collection publishes something
about their sample number 10,000 and it is known that the person does

not
have anywhere near 10,000 samples, it would be viewed as odd at the very
least, possibly unethical and such a person would find himself not taken
seriously by other researchers. One or two numbers amiss in this

situation
is obviously not a major concern.

And for the internal inventory controls, if someone sees sample 152 next


to

150, they are going to wonder where is number 151. The inventory methods
used expect sequential numbering and a missing number is an indication

of
something wrong. For inventory numbers in the original database, she

used
the record number that appears in the text box of Access's navigation
control in conjunction with an autonumber field. You may guess what sort


of

hash resulted from that. I started out trying to fix a few things for

her
and wound up doing almost a complete re-write of the entire thing and

this
numbering issue is one of the things that surfaced. She wants to be able


to

fill in all the gaps as well as add new numbers to the end as she

collects
new samples.

Pete


"David C. Holley" píse v diskusním príspevku
.. .

What is the specific *NEED* to find the missing numbers?

Peter Danes wrote:

I occasionally need to determine a number that I don't have in a
sequence, either the first missing one in a gap in a set of sequential
numbers or the next one in line at the end of a numbered series.

Always
it meant some fumbling around, with either VBA at first or later with


SQL

when I got good enough at it, establishing the proper join parameters


and

such. For SQL experts, this is probably routine and trivial, but for

me
it was always a bit of a chore. The last straw came with a database


which

I recently wrote, where the converted data had such a numbered series,
and the owner wanted to be able to do both, fill in missing numbers in
the gaps AND add new numbers at the end.

Walking home from a bar last night, I got to thinking about it and
realized that both problems are actually fairly similar and that a


simple

and general solution is possible.
I put together a simple table containing one field with the following
entries:

1,2,3,4, 8,9,10, 15,16,17,18, 20, 22,23,24,25, 28,29,30

Missing a


5,6,7, 11,12,13,14, 19, 21, 26,27 and 31 on up.

This is the dataset used for all of the following examples.


Finding the next new number at the end of a series with SQL is

trivial;
here is a simplified version of a statement that I found somewhere in


the

discussion groups a few years ago:

SELECT Max(MyTable.MySeqFld)+1 FROM MyTable;

This will return a one-record, one-field recordset containing exactly


one

value: 31, which is one greater than the largest value so far used in
that field. This is what you would want to use instead of Access's
autonumber, if the field is to contain meaningful sequence numbering,
rather than just a unique identifier.

Locating gaps is a little more complicated: it involves a self-join


from

N to N+1 and finding where N+1 doesn't exist, indicating a gap at that
point.

SELECT MT1.MySeqFld+1
FROM MyTable AS MT1 LEFT JOIN MyTable AS MT2 ON
MT1.MySeqFld+1=MT2.MySeqFld
WHERE MT2.MySeqFld IS NULL;

This generates a recordset of 5, 11, 19, 21, 26, 31, where each value


is

the first missing value in a gap, including the "open gap" at the end,
and that's where the trick to a general solution begins. Since these
situations normally call for either the first (lowest number) gap or


last

(end of recordset) gap, you need either the first or last record


returned

by this query. Sorting and using the TOP predicate gives you exactly
that.

SELECT TOP 1 MT1.MySeqFld+1
FROM MyTable AS MT1 LEFT JOIN MyTable AS MT2 ON
MT1.MySeqFld+1=MT2.MySeqFld
WHERE MT2.MySeqFld IS NULL
ORDER BY MT1.MySeqFld;

This will again return a one-record, one-field recordset containing
exactly one value: 5, the first missing number in the first gap in the
sequence. Ascending sort order is the default, so the smallest number


is

the first returned.

SELECT TOP 1 MT1.MySeqFld+1
FROM MyTable AS MT1 LEFT JOIN MyTable AS MT2 ON
MT1.MySeqFld+1=MT2.MySeqFld
WHERE MT2.MySeqFld IS NULL
ORDER BY MT1.MySeqFld DESC;

This will return a one-record, one-field recordset containing exactly


one

value: 31, the same "one greater than the highest value so far used in
that field" that is returned by the first simple example. Specifying


the

descending order here is necessary, since we want the last (greatest)
record from the set and Access SQL does not have a BOTTOM predicate.

Finally, an even more general statement can be used:

SELECT TOP 1 MT1.MySeqFld+1
FROM MyTable AS MT1 LEFT JOIN MyTable AS MT2 ON
MT1.MySeqFld+1=MT2.MySeqFld
WHERE MT2.MySeqFld IS NULL
ORDER BY ((INSTR("LF",[First or Last (F or L)]) *2)-3)*MT1.MySeqFld;

This expects one parameter, F or L and will return either the first
missing number or the next number at the end of the line. The INSTR
expression evaluates to either -1 or 1 (or -3 if the parameter

supplied
is neither F nor L, but that has the same effect as -1 in this


instance),

that is then used as a multiplier for the sort field, so the sort is
either by the field or by the negative of the field (or 3 times the
negative of the field), giving either ascending or descending order

and
with the TOP 1 predicate again returns exactly the one value of


interest.





  #25  
Old December 6th, 2005, 06:00 PM posted to microsoft.public.access,microsoft.public.access.queries,microsoft.public.access.formscoding
external usenet poster
 
Posts: n/a
Default General solution for missing sequence numbers

Certainly that is one possible way to do it, but in this case I'm not
interested in ALL the missing numbers. I only want to know which one is the
next one available for use, either the first one in the first gap, or the
next one greater than all the ones used so far. This allows me to fetch that
one number with this single SQL statement, rather than looping through a
recordset with VBA. And a side benefit is that SQL is orders of magnitude
faster than such a VBA loop.

--
Pete



"David C. Holley" píse v diskusním príspevku
...
Have you thought about using a DAO approach where you loop through the
records one by one and compare the current value to the previous?

Peter Danes wrote:
There are three differences:

1. Your example is the same as my first example which returns only the
"greatest +1", except that you additionally include an alias to the

table,
the "AS MT1" at the end of the statement. It doesn't hurt anything, but
isn't really necessary.

2. Youe example doesn't call for a parameter, mine does, to determine

the
sort order and so whether you get the first missing number or the next

in
line greater than all numbers used so far.

3. Obviously, the example you posted is considerably simpler, and if you
only need what it returns, simpler is preferable. The point of my

'lecture'
was simply that a general solution to these related problems is possible
with a single SQL statement. I do not claim that it is preferable in all
situations, or even any particular situation.

Pete


"Chris2" píše v

diskusním
příspěvku ...

"Peter Danes" wrote in message
.. .

snip

SELECT TOP 1 MT1.MySeqFld+1
FROM MyTable AS MT1 LEFT JOIN MyTable AS MT2 ON

MT1.MySeqFld+1=MT2.MySeqFld

WHERE MT2.MySeqFld IS NULL
ORDER BY MT1.MySeqFld DESC;

This will return a one-record, one-field recordset containing

exactly one

value: 31, the same "one greater than the highest value so far

used in that

field" that is returned by the first simple example. Specifying

the

descending order here is necessary, since we want the last

(greatest) record

from the set and Access SQL does not have a BOTTOM predicate.

Peter Danes,

I am not sure what the difference is between the above and the
below.

SELECT MAX(MT1.MySeqFld) + 1
FROM MyTable AS MT1;


Sincerely,

Chris O.







  #26  
Old December 6th, 2005, 06:11 PM posted to microsoft.public.access,microsoft.public.access.queries,microsoft.public.access.formscoding
external usenet poster
 
Posts: n/a
Default General solution for missing sequence numbers

Yes, some cannot. In particular, a self-join cannot (as far as I know),
which is exactly what I used here. I'm not certain that I agree with the
notion that SQL is more readable with aliases than without, it seems to me
to be just one more re-direction that must be kept in mind when tracking or
debugging a statement. But that's just my opinion, worth exactly what you
paid for it. And I'm far from being a SQL expert, you may be right. I'd be
interested in your thoughts on how it improves readability.

And as for the question, well, I was just answering it - I didn't mean to
sound snippy. The way you worded it made me think that you really didn't
know what the difference between the statements was, but if you've been
writing SQL queries for years, you probably know more about it than I do.

--
Pete



"Chris2" píše v diskusním
příspěvku ...

"Peter Danes" wrote in message
...
"Chris2"

"Peter Danes" wrote in message
...

snip


snip



Sincerely,

Chris O.



There are three differences:

1. Your example is the same as my first example which returns only

the
"greatest +1", except that you additionally include an alias to

the table,
the "AS MT1" at the end of the statement. It doesn't hurt

anything, but
isn't really necessary.


Using table aliases may not be necessary, but I haven't written a
query more complicated than SELECT * FROM table_name in years
without them. The readability of SQL is greatly improved by their
use, and some queries cannot be written without them.

In any event, table aliases were not the purpose of my post.

I was only asking a question.


Sincerely,

Chris O.




  #27  
Old December 6th, 2005, 06:14 PM posted to microsoft.public.access,microsoft.public.access.queries,microsoft.public.access.formscoding
external usenet poster
 
Posts: n/a
Default General solution for missing sequence numbers

On Tue, 6 Dec 2005 15:56:01 +0100, "Peter Danes"
wrote:

The gaps got there in the first place because the owner of the database is a
scientist, not a computer tech.


Well, so am I, if it comes to that (Ph.D. Chemistry, Berkeley 1972).
No academic training in computers beyond a Fortran course back in
1968.

It doesn't really address the issue of why NEW records should backfill
the holes left in this earlier process, but by all means, if that's
what they want, you clearly have several sets of tools to do so. Just
another one for the toolkit: I routinely include a table Num with a
single field N, values 0 to 65536 or so. An "unmatched" query joining
Num to the table will very promptly provide all unused numbers, which
can then be assigned to new records.

John W. Vinson[MVP]
  #28  
Old December 6th, 2005, 06:58 PM posted to microsoft.public.access,microsoft.public.access.queries,microsoft.public.access.formscoding
external usenet poster
 
Posts: n/a
Default General solution for missing sequence numbers

Thank you, James. Always neat to learn another way of doing something.

--
Pete



"James A. Fortune" píse v diskusním príspevku
...
Peter Danes wrote:
I occasionally need to determine a number that I don't have in a

sequence,
either the first missing one in a gap in a set of sequential numbers or

the
next one in line at the end of a numbered series. Always it meant some
fumbling around, with either VBA at first or later with SQL when I got

good
enough at it, establishing the proper join parameters and such. For SQL
experts, this is probably routine and trivial, but for me it was always

a
bit of a chore. The last straw came with a database which I recently

wrote,
where the converted data had such a numbered series, and the owner

wanted to
be able to do both, fill in missing numbers in the gaps AND add new

numbers
at the end.

Walking home from a bar last night, I got to thinking about it and

realized
that both problems are actually fairly similar and that a simple and

general
solution is possible.
I put together a simple table containing one field with the following
entries:

1,2,3,4, 8,9,10, 15,16,17,18, 20, 22,23,24,25, 28,29,30

Missing a


5,6,7, 11,12,13,14, 19, 21, 26,27 and 31 on up.

This is the dataset used for all of the following examples.


Finding the next new number at the end of a series with SQL is trivial;

here
is a simplified version of a statement that I found somewhere in the
discussion groups a few years ago:

SELECT Max(MyTable.MySeqFld)+1 FROM MyTable;

This will return a one-record, one-field recordset containing exactly

one
value: 31, which is one greater than the largest value so far used in

that
field. This is what you would want to use instead of Access's

autonumber, if
the field is to contain meaningful sequence numbering, rather than just

a
unique identifier.

Locating gaps is a little more complicated: it involves a self-join from

N
to N+1 and finding where N+1 doesn't exist, indicating a gap at that

point.

SELECT MT1.MySeqFld+1
FROM MyTable AS MT1 LEFT JOIN MyTable AS MT2 ON

MT1.MySeqFld+1=MT2.MySeqFld
WHERE MT2.MySeqFld IS NULL;

This generates a recordset of 5, 11, 19, 21, 26, 31, where each value is

the
first missing value in a gap, including the "open gap" at the end, and
that's where the trick to a general solution begins. Since these

situations
normally call for either the first (lowest number) gap or last (end of
recordset) gap, you need either the first or last record returned by

this
query. Sorting and using the TOP predicate gives you exactly that.

SELECT TOP 1 MT1.MySeqFld+1
FROM MyTable AS MT1 LEFT JOIN MyTable AS MT2 ON

MT1.MySeqFld+1=MT2.MySeqFld
WHERE MT2.MySeqFld IS NULL
ORDER BY MT1.MySeqFld;

This will again return a one-record, one-field recordset containing

exactly
one value: 5, the first missing number in the first gap in the sequence.
Ascending sort order is the default, so the smallest number is the first
returned.

SELECT TOP 1 MT1.MySeqFld+1
FROM MyTable AS MT1 LEFT JOIN MyTable AS MT2 ON

MT1.MySeqFld+1=MT2.MySeqFld
WHERE MT2.MySeqFld IS NULL
ORDER BY MT1.MySeqFld DESC;

This will return a one-record, one-field recordset containing exactly

one
value: 31, the same "one greater than the highest value so far used in

that
field" that is returned by the first simple example. Specifying the
descending order here is necessary, since we want the last (greatest)

record
from the set and Access SQL does not have a BOTTOM predicate.

Finally, an even more general statement can be used:

SELECT TOP 1 MT1.MySeqFld+1
FROM MyTable AS MT1 LEFT JOIN MyTable AS MT2 ON

MT1.MySeqFld+1=MT2.MySeqFld
WHERE MT2.MySeqFld IS NULL
ORDER BY ((INSTR("LF",[First or Last (F or L)]) *2)-3)*MT1.MySeqFld;

This expects one parameter, F or L and will return either the first

missing
number or the next number at the end of the line. The INSTR expression
evaluates to either -1 or 1 (or -3 if the parameter supplied is neither

F
nor L, but that has the same effect as -1 in this instance), that is

then
used as a multiplier for the sort field, so the sort is either by the

field
or by the negative of the field (or 3 times the negative of the field),
giving either ascending or descending order and with the TOP 1 predicate
again returns exactly the one value of interest.



An alternative SQL method using subqueries can be found he


http://groups.google.com/group/micro...4a5fee9ff13437

James A. Fortune

I was staying at a hotel and decided to go down to the pool. A 13 year
old bratty kid splashed water on me. When I told him to stop he said,
"You can't make me. I'm a minor. If you touch me you'll get in a lot
of trouble." I found a 17 year old at the pool and paid him $5 to hold
the kid underwater for 10 seconds. "How do you like me now?" -- Rob

Smith


  #29  
Old December 6th, 2005, 07:16 PM posted to microsoft.public.access,microsoft.public.access.queries,microsoft.public.access.formscoding
external usenet poster
 
Posts: n/a
Default General solution for missing sequence numbers

That's a good trick, too. Thanks.

--
Pete



"John Vinson" píse v diskusním
príspevku ...
On Tue, 6 Dec 2005 15:56:01 +0100, "Peter Danes"
wrote:

The gaps got there in the first place because the owner of the database

is a
scientist, not a computer tech.


Well, so am I, if it comes to that (Ph.D. Chemistry, Berkeley 1972).
No academic training in computers beyond a Fortran course back in
1968.

It doesn't really address the issue of why NEW records should backfill
the holes left in this earlier process, but by all means, if that's
what they want, you clearly have several sets of tools to do so. Just
another one for the toolkit: I routinely include a table Num with a
single field N, values 0 to 65536 or so. An "unmatched" query joining
Num to the table will very promptly provide all unused numbers, which
can then be assigned to new records.

John W. Vinson[MVP]



  #30  
Old December 7th, 2005, 04:03 AM posted to microsoft.public.access,microsoft.public.access.queries,microsoft.public.access.formscoding
external usenet poster
 
Posts: n/a
Default General solution for missing sequence numbers


"Peter Danes" wrote in message
...
I'd be interested in your thoughts on how it improves readability.


Less text equals less to read equals greater readability. (See
below and consider.)

If the aliases are named correctly, then you automatically know what
tables they refer to.

Access, with it's penchant for re-arranging the SQL of queries,
especially for cutting out line-breaks, doesn't help much in the way
of readability, so it needs all the help it can get.

I'll admit most Access users don't care, as they use Design View
instead of SQL View. I use SQL View almost all the time.


Example: From a query in a thread (Group By Last, by Barrattolo_67).

Note: This is also a good example of why not to use spaces, as it
introduces masses of readability reducing brackets (not to mention
the other reasons).

Vanila MS Access Unmodified Query w/Spaces in Object Names:

INSERT INTO [Audit Follow-up Report] ( [No], [Thrust Area], [Title
of
Issue], [Risk Severity Code], Recommendation, [Responsible
Department],
[Management Action Plan], [Target Completion Date], [Revised Target
Date],
[Actual Completion Date], [Follow-up Status], [Change History],
[Management
Status Description], [Auditor's Comments] )
SELECT [tbl Comments].[Order of appearance], [tbl Comments].[Cycle
Name],
[tbl Comments].[Comment Title], [tbl Comments].[Risk Severity Code],
First([tbl Comments].Recommendation) AS FirstOfRecommendation, [tbl
Management Responses].[Responsible Department], First([tbl
Management
Responses].[Management Action Plan]) AS [FirstOfManagement Action
Plan], [tbl
Management Responses].[Target Completion Date], [tbl Management
Responses].RevisedTargetDate, [tbl Management Responses].[Actual
Completion
Date], [tbl Follow-up status codes].[Follow-up status code], [tbl
Management
Responses].[Completion Date Change History and Other Comments],
First([tbl
Follow-up Entries for Findings].[Management's Status Description])
AS
[FirstOfManagement's Status Description], First([tbl Follow-up
Entries for
Findings].[Auditor Comments]) AS [FirstOfAuditor Comments]
FROM ([tbl Comments] LEFT JOIN ([tbl Follow-up status codes] RIGHT
JOIN [tbl
Management Responses] ON [tbl Follow-up status codes].[Follow-up
status
order] = [tbl Management Responses].[Follow-up status code]) ON [tbl
Comments].[Comment Table counter] = [tbl Management
Responses].[Comment Table
counter]) LEFT JOIN [tbl Follow-up Entries for Findings] ON [tbl
Management
Responses].[ID for tbl Management Responses] = [tbl Follow-up
Entries for
Findings].[ID in tbl Management Responses]
GROUP BY [tbl Comments].[Order of appearance], [tbl Comments].[Cycle
Name],
[tbl Comments].[Comment Title], [tbl Comments].[Risk Severity Code],
[tbl
Management Responses].[Responsible Department], [tbl Management
Responses].[Target Completion Date], [tbl Management
Responses].RevisedTargetDate, [tbl Management Responses].[Actual
Completion
Date], [tbl Follow-up status codes].[Follow-up status code], [tbl
Management
Responses].[Completion Date Change History and Other Comments], [tbl
Comments].[Audit Report #]
HAVING ((([tbl Comments].[Audit Report #])="FA-BDI-04-34"))
ORDER BY [tbl Comments].[Order of appearance];


Query Re-Aligned (note the line-breaks caused by the enormous length
of some of the lines.

INSERT INTO [Audit Follow-up Report]
([No]
,[Thrust Area]
,[Title of Issue]
,[Risk Severity Code]
,Recommendation
,[Responsible Department]
,[Management Action Plan]
,[Target Completion Date]
,[Revised Target Date]
,[Actual Completion Date]
,[Follow-up Status]
,[Change History]
,[Management Status Description]
,[Auditor's Comments])
SELECT [tbl Comments].[Order of appearance]
,[tbl Comments].[Cycle Name]
,[tbl Comments].[Comment Title]
,[tbl Comments].[Risk Severity Code]
,First([tbl Comments].Recommendation) AS
FirstOfRecommendation
,[tbl Management Responses].[Responsible Department]
,First([tbl Management Responses].[Management Action Plan])
AS [FirstOfManagement Action Plan]
,[tbl Management Responses].[Target Completion Date]
,[tbl Management Responses].RevisedTargetDate
,[tbl Management Responses].[Actual Completion Date]
,[tbl Follow-up status codes].[Follow-up status code]
,[tbl Management Responses].[Completion Date Change History
and Other Comments]
,First([tbl Follow-up Entries for Findings].[Management's
Status Description]) AS [FirstOfManagement's Status Description]
,First([tbl Follow-up Entries for Findings].[Auditor
Comments]) AS [FirstOfAuditor Comments]
FROM ([tbl Comments]
LEFT JOIN
([tbl Follow-up status codes]
RIGHT JOIN
[tbl Management Responses]
ON [tbl Follow-up status codes].[Follow-up status order] =
[tbl Management Responses].[Follow-up status code])
ON [tbl Comments].[Comment Table counter] =
[tbl Management Responses].[Comment Table counter])
LEFT JOIN
[tbl Follow-up Entries for Findings]
ON [tbl Management Responses].[ID for tbl Management
Responses] =
[tbl Follow-up Entries for Findings].[ID in tbl Management
Responses]
GROUP BY [tbl Comments].[Order of appearance]
,[tbl Comments].[Cycle Name]
,[tbl Comments].[Comment Title]
,[tbl Comments].[Risk Severity Code]
,[tbl Management Responses].[Responsible Department]
,[tbl Management Responses].[Target Completion Date]
,[tbl Management Responses].RevisedTargetDate
,[tbl Management Responses].[Actual Completion Date]
,[tbl Follow-up status codes].[Follow-up status code]
,[tbl Management Responses].[Completion Date Change History
and Other Comments]
,[tbl Comments].[Audit Report #]
HAVING ((([tbl Comments].[Audit Report #])="FA-BDI-04-34"))
ORDER BY [tbl Comments].[Order of appearance];


Query w/Table Aliases:

INSERT INTO [Audit Follow-up Report]
([No]
,[Thrust Area]
,[Title of Issue]
,[Risk Severity Code]
,Recommendation
,[Responsible Department]
,[Management Action Plan]
,[Target Completion Date]
,[Revised Target Date]
,[Actual Completion Date]
,[Follow-up Status]
,[Change History]
,[Management Status Description]
,[Auditor's Comments])
SELECT CO1.[Order of appearance]
,CO1.[Cycle Name]
,CO1.[Comment Title
,CO1.[Risk Severity Code]
,First(CO1.Recommendation) AS FirstOfRecommendation
,MR1.[Responsible Department]
,First(MR1.[Management Action Plan]) AS [FirstOfManagement
Action Plan]
,MR1.[Target Completion Date]
,MR1.RevisedTargetDate
,MR1.[Actual Completion Date]
,FU1.[Follow-up status code]
,MR1.[Completion Date Change History and Other Comments]
,First(FE1.[Management's Status Description]) AS
[FirstOfManagement's Status Description]
,First(FE1.[Auditor Comments]) AS [FirstOfAuditor Comments]
FROM ([tbl Comments] AS CO1
LEFT JOIN
([tbl Follow-up status codes] AS FU1
RIGHT JOIN
[tbl Management Responses] AS MR1
ON FU1.[Follow-up status order] =
MR1.[Follow-up status code])
ON CO1.[Comment Table counter] =
MR1.[Comment Table counter])
LEFT JOIN
[tbl Follow-up Entries for Findings] FE1
ON MR1.[ID for tbl Management Responses] =
FE1.[ID in tbl Management Responses]
GROUP BY CO1.[Order of appearance]
,CO1.[Cycle Name]
,CO1.[Comment Title]
,CO1.[Risk Severity Code]
,MR1.[Responsible Department]
,MR1.[Target Completion Date]
,MR1.RevisedTargetDate
,MR1.[Actual Completion Date]
,FU1.[Follow-up status code]
,MR1.[Completion Date Change History and Other Comments]
,CO1.[Audit Report #]
HAVING (((CO1.[Audit Report #])="FA-BDI-04-34"))
ORDER BY CO1.[Order of appearance];


Query w/out spaces in object names and w/out accompanying brackets
and w/out table object prefixes. I left the column aliases (for
output) alone.

INSERT INTO AuditFollowUpReport
(Nbr
,ThrustArea
,TitleOfIssue
,RiskSeverityCode
,Recommendation
,ResponsibleDepartment
,ManagementActionPlan
,TargetCompletionDate
,RevisedTargetDate
,ActualCompletionDate
,FollowUpStatus
,ChangeHistory
,ManagementStatusDescription
,AuditorsComments)
SELECT CO1.OrderOfAppearance
,CO1.CycleName
,CO1.CommentTitle
,CO1.RiskSeverityCode
,First(CO1.Recommendation)
AS [FirstOfRecommendation]
,MR1.ResponsibleDepartment
,First(MR1.ManagementActionPlan)
AS [FirstOfManagement Action Plan]
,MR1.TargetCompletionDate
,MR1.RevisedTargetDate
,MR1.ActualCompletionDate
,FU1.FollowUpStatusCode
,MR1.CompletionDateChangeHistoryAndOtherComments
,First(FE1.ManagementsStatusDescription)
AS [FirstOfManagement's Status Description]
,First(FE1.AuditorComments)
AS [FirstOfAuditor Comments]
FROM (Comments AS CO1
LEFT JOIN
(FollowUpStatusCodes AS FU1
RIGHT JOIN
ManagementResponses AS MR1
ON FU1.FollowUpStatusOrder =
MR1.FollowUpStatusCode)
ON CO1.CommentTableCounter =
MR1.CommentTableCounter)
LEFT JOIN
FollowUpEntriesForFindings FE1
ON MR1.IDForTblManagementResponses =
FE1.IDInTblManagementResponses
GROUP BY CO1.OrderOfAppearance
,CO1.CycleName
,CO1.CommentTitle
,CO1.RiskSeverityCode
,MR1.ResponsibleDepartment
,MR1.TargetCompletionDate
,MR1.RevisedTargetDate
,MR1.ActualCompletionDate
,FU1.FollowUpStatusCode
,MR1.CompletionDateChangeHistoryAndOtherComments
,CO1.AuditReportNbr
HAVING (((CO1.AuditReportNbr) = "FA-BDI-04-34"))
ORDER BY CO1.OrderOfAppearance;

It simply looks far more readable to me.

Access does mangle it right away after saving and closing the window
.. . . sigh /.

INSERT INTO AuditFollowUpReport ( Nbr, ThrustArea, TitleOfIssue,
RiskSeverityCode, Recommendation, ResponsibleDepartment,
ManagementActionPlan, TargetCompletionDate, RevisedTargetDate,
ActualCompletionDate, FollowUpStatus, ChangeHistory,
ManagementStatusDescription, AuditorsComments )
SELECT CO1.OrderOfAppearance, CO1.CycleName, CO1.CommentTitle,
CO1.RiskSeverityCode, First(CO1.Recommendation) AS
FirstOfRecommendation, MR1.ResponsibleDepartment,
First(MR1.ManagementActionPlan) AS [FirstOfManagement Action Plan],
MR1.TargetCompletionDate, MR1.RevisedTargetDate,
MR1.ActualCompletionDate, FU1.FollowUpStatusCode,
MR1.CompletionDateChangeHistoryAndOtherComments,
First(FE1.ManagementsStatusDescription) AS [FirstOfManagement's
Status Description], First(FE1.AuditorComments) AS [FirstOfAuditor
Comments]
FROM (Comments AS CO1 LEFT JOIN (FollowUpStatusCodes AS FU1 RIGHT
JOIN ManagementResponses AS MR1 ON
FU1.FollowUpStatusOrder=MR1.FollowUpStatusCode) ON
CO1.CommentTableCounter=MR1.CommentTableCounter) LEFT JOIN
FollowUpEntriesForFindings AS FE1 ON
MR1.IDForTblManagementResponses=FE1.IDInTblManagem entResponses
GROUP BY CO1.OrderOfAppearance, CO1.CycleName, CO1.CommentTitle,
CO1.RiskSeverityCode, MR1.ResponsibleDepartment,
MR1.TargetCompletionDate, MR1.RevisedTargetDate,
MR1.ActualCompletionDate, FU1.FollowUpStatusCode,
MR1.CompletionDateChangeHistoryAndOtherComments, CO1.AuditReportNbr
HAVING (((CO1.AuditReportNbr) = "FA-BDI-04-34"))
ORDER BY CO1.OrderOfAppearance;

But the left over results are still more readable than the original.


Sincerely,

Chris O.


 




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