Reading a file without a SELECT list?

+4

Jonathan Smith
Rocketeer
Forum|Forum|2 years ago
May 24, 2023

I finished my contract last week, so back on the market. I landed an interview with a "recognizable company" and went straight to the final round.

During the interview one of the panel asked me, "How do you read a file without a select list?" I paused for a moment wondering why anyone would need to do that? I thought for a moment and came to the conclusion, it may be possible, but I cannot think of how it could be done. I responded to him, "In the twenty years I've worked in multivalue, I have never seen any code that would do that. But I don't ever recall ever having the need".

Is it possible? Does anyone have an example?

Added: This person meant without using SELECT anywhere. At TCL or internally in a program. He claims he has a way, I doubt him.

------------------------------
Scott Johnston
Sr Software Engineer, Architect & Developer
Dover DE US
------------------------------

Scott,

A SELECT statement against a file variable does not create a SELECT list, where a SELECT file at TCL / ECL does. It process the file group by group (aka hash order) and starts straight away without any delay, there are other limitations around doing this around but that's anthoer discussion.

OPEN "CUSTOMER" TO F.CUSTOMER ELSE ...
SELECT F.CUSTOMER TO 5
EOF = @FALSE
LOOP
READNEXT K.CUSTOMER FROM 5 ELSE EOF = @TRUE
UNTIL EOF DO
...
REPEAT

------------------------------
Jonathan Smith
UniData ATS
Rocket Support
------------------------------

UniData ATS

Like

S

Scott Johnston
Author
Participating Frequently
Forum|Forum|2 years ago
May 24, 2023

Scott,

A SELECT statement against a file variable does not create a SELECT list, where a SELECT file at TCL / ECL does. It process the file group by group (aka hash order) and starts straight away without any delay, there are other limitations around doing this around but that's anthoer discussion.

OPEN "CUSTOMER" TO F.CUSTOMER ELSE ...
SELECT F.CUSTOMER TO 5
EOF = @FALSE
LOOP
READNEXT K.CUSTOMER FROM 5 ELSE EOF = @TRUE
UNTIL EOF DO
...
REPEAT

------------------------------
Jonathan Smith
UniData ATS
Rocket Support
------------------------------

That's still creates a selection in memory and you are USING a SELECT statement. This persons claim question was how can you read a file without using a SELECT statement, which always creates a list.

I'll edit that post to make it clearer.

------------------------------
Scott Johnston
Sr Architect &n Developer
Sonna Solutions
Dover DE US
------------------------------

Like

+4

Jonathan Smith
Rocketeer
Forum|Forum|2 years ago
May 24, 2023

That's still creates a selection in memory and you are USING a SELECT statement. This persons claim question was how can you read a file without using a SELECT statement, which always creates a list.

I'll edit that post to make it clearer.

------------------------------
Scott Johnston
Sr Architect &n Developer
Sonna Solutions
Dover DE US
------------------------------

Scott,

If you want the simplist way I can think of without a SELECT statement. Create an Index on the file of @ID. Use the SETINDEX command to position the program at the first index key in the index and then use the READFWD command. READFWD also has READFWDU and READFWDL to lock records as well.

OPEN "CUSTOMER" TO F.CUSTOMER ELSE STOP
SETINDEX "@ID" ON F.CUSTOMER
EOF = @FALSE
LOOP
READFWD R.CUSTOMER FROM F.CUSTOMER ELSE EOF = @TRUE
UNTIL EOF DO
CRT @ID : " " : R.CUSTOMER
REPEAT
END

Your original question as per the subject was without a SELECT list. The SELECT statement in Basic of a file variable, simply tells UniData or UniVerse to read through the file group by group and record by record as they are stored in the file. It does not create a list or a selection in memory, it simply sets a pointer to keep track of pointer to the next record (or record id in the id list in UniData) to process. In UniVerse it follows the forward pointer to next record in the group to get the next item id, in UniData it just goes through the list of item ids stored in the first part of the file (the UniData file structure is different to UniVerse in that it is not a doubly linked list, the top part of the group contains a list of item ids with pointers to where the data is in the second part of the group).

So based on the original description of not using a SELECT list, the SELECT of file variable does not generate a list and in terms of how it proceses it simply updates a pointer to the next item id after the READNEXT is executed.

I do have utiltiy programs that use commands commands such as OSBREAD in UniData and READBLK in UniVerse to go through a file block by block, these don't require any SELECT statement just an understanding of the internal file structures.

There are some low level tools (fileview in UniData for example) which can display the records in each group of the file, so that would be one very complicated way of doing it, as are the OSBREAD and READBLK methods above without knowing the internals of the file structures.

I'll be interested to see if anyone has a simple of way of doing this is Basic without using a SELECT statement of any type and not utilizing SETINDEX and READFWD.

------------------------------
Jonathan Smith
UniData ATS
Rocket Support
------------------------------

UniData ATS

Like

M

Marcus Rhodes
Participating Frequently
Forum|Forum|2 years ago
May 24, 2023

Scott,

A SELECT statement against a file variable does not create a SELECT list, where a SELECT file at TCL / ECL does. It process the file group by group (aka hash order) and starts straight away without any delay, there are other limitations around doing this around but that's anthoer discussion.

OPEN "CUSTOMER" TO F.CUSTOMER ELSE ...
SELECT F.CUSTOMER TO 5
EOF = @FALSE
LOOP
READNEXT K.CUSTOMER FROM 5 ELSE EOF = @TRUE
UNTIL EOF DO
...
REPEAT

------------------------------
Jonathan Smith
UniData ATS
Rocket Support
------------------------------

It might me more accurate to say that when selecting a file variable, the file itself *is* the list, and it's processed in logical order (the order in which the records are 'physically' laid out on the disk) , whereas, when a TCL select is executed, a separate list must be generated, usually in a hidden, temporary file. But not all flavors retain the entire list in RAM. In fact, I doubt any do. UniData, for example, splits big lists up into 32K chunks, and loads/processes them individually so as to save RAM. You can see this by saving the list and editing the resulting items in the savedlists file.

This is why the preferred method for reading host OS files sequentially (at least on Pick) used to be to select them as as savedlists, and then get the list. No way would it load the entire file into RAM. It would just take the next item, just like a readseq does now.

An interesting experiment would be to build a dynamic list in a program, and then process that list, deleting the top attribute after each loop. Then compare this to using the TCL select, and then the BASIC select.

------------------------------
Marcus Rhodes
marcus1@thinqware.com
------------------------------

Like

+4

Jonathan Smith
Rocketeer
Forum|Forum|2 years ago
May 24, 2023

It might me more accurate to say that when selecting a file variable, the file itself *is* the list, and it's processed in logical order (the order in which the records are 'physically' laid out on the disk) , whereas, when a TCL select is executed, a separate list must be generated, usually in a hidden, temporary file. But not all flavors retain the entire list in RAM. In fact, I doubt any do. UniData, for example, splits big lists up into 32K chunks, and loads/processes them individually so as to save RAM. You can see this by saving the list and editing the resulting items in the savedlists file.

This is why the preferred method for reading host OS files sequentially (at least on Pick) used to be to select them as as savedlists, and then get the list. No way would it load the entire file into RAM. It would just take the next item, just like a readseq does now.

An interesting experiment would be to build a dynamic list in a program, and then process that list, deleting the top attribute after each loop. Then compare this to using the TCL select, and then the BASIC select.

------------------------------
Marcus Rhodes
marcus1@thinqware.com
------------------------------

Hi Marcus,

The spliting of savedlists into 32K chuck files was changed in UniData 8.1.0 back in 2014. A udtconfig item SINGLE_SAVEDLIST was added with the default value of 1. Any savedlist saved or created with this set is created as a single item without chunking. The 32K limit was based on a very old and obselete value of the largest record that could be read into UniData. So from 8.1.0, the whole list without chunking is loaded into memory as an array.

UniData also has an internal 'remove pointer' when it comes to processing arrays at an attribute level, which matches the speed of the REMOVE statement / function (this was extended to multivalue and subvalues in 8.2.1 in 2020). You can process through huge arrays accessing them attribute or attribute via a FOR NEXT loop or REMOVE statement. Deleting the top attribute requires using memory based operations around copying, so I would expect processing an array attribute by attribute using a FOR ... NEXT or REMOVE would be really quick.

Please also see my earlier post on how 'SELECT filevariable' works and a way to do the processing without using a SELECT statement at all using SETINDEX and READFWD.

Thanks,

------------------------------
Jonathan Smith
UniData ATS
Rocket Support
------------------------------

UniData ATS

Like

A

Anonymous
Forum|Forum|2 years ago
May 25, 2023

I finished my contract last week, so back on the market. I landed an interview with a "recognizable company" and went straight to the final round.

During the interview one of the panel asked me, "How do you read a file without a select list?" I paused for a moment wondering why anyone would need to do that? I thought for a moment and came to the conclusion, it may be possible, but I cannot think of how it could be done. I responded to him, "In the twenty years I've worked in multivalue, I have never seen any code that would do that. But I don't ever recall ever having the need".

Is it possible? Does anyone have an example?

Added: This person meant without using SELECT anywhere. At TCL or internally in a program. He claims he has a way, I doubt him.

------------------------------
Scott Johnston
Sr Software Engineer, Architect & Developer
Dover DE US
------------------------------

Scott,

It is possible and in some cases the only way to perform some tasks. The simple case is when you process a file of all cardinal integers. You only need the primary key staring with 1 and process until there are no more records. No select was required. In a B-TREE indexing system you have a root key and then the other index and leaf keys are all link listed to the root record. No select required. Very fast and efficient.

As Pick BASIC programmers we see the world through multivalued glasses. There are other programming methodologies that exist outside of Pick.

Jon

------------------------------
Jon Kristofferson
Pick Programmer
Snap-on Credit LLC
Libertyville IL US
------------------------------

Like

Sam Powell
Participating Frequently
Forum|Forum|2 years ago
May 25, 2023

I finished my contract last week, so back on the market. I landed an interview with a "recognizable company" and went straight to the final round.

During the interview one of the panel asked me, "How do you read a file without a select list?" I paused for a moment wondering why anyone would need to do that? I thought for a moment and came to the conclusion, it may be possible, but I cannot think of how it could be done. I responded to him, "In the twenty years I've worked in multivalue, I have never seen any code that would do that. But I don't ever recall ever having the need".

Is it possible? Does anyone have an example?

Added: This person meant without using SELECT anywhere. At TCL or internally in a program. He claims he has a way, I doubt him.

------------------------------
Scott Johnston
Sr Software Engineer, Architect & Developer
Dover DE US
------------------------------

Hi Scott:

It could also be someone who doesn't completely understand the internals and thought that if you did a simple LIST ... it's a way of reading records without an 'actual' SELECT. It could have also been referring to the FORMLIST Basic command to turn a dynamic array into 'select' list.

Did he ever provide an answer?

Sam

------------------------------
Samuel A Powell
President/Developer
Advanced Transportation Systems Inc
Colorado Springs CO US
------------------------------

Like

Tyrel Marak
Participating Frequently
Forum|Forum|2 years ago
May 25, 2023

Scott,

It is possible and in some cases the only way to perform some tasks. The simple case is when you process a file of all cardinal integers. You only need the primary key staring with 1 and process until there are no more records. No select was required. In a B-TREE indexing system you have a root key and then the other index and leaf keys are all link listed to the root record. No select required. Very fast and efficient.

As Pick BASIC programmers we see the world through multivalued glasses. There are other programming methodologies that exist outside of Pick.

Jon

------------------------------
Jon Kristofferson
Pick Programmer
Snap-on Credit LLC
Libertyville IL US
------------------------------

Jon,

Are you meaning that with foreknowledge of a file's key structure (necessarily simple) and/or indexes, then you can bypass the need to select and go straight to reading? The original post seemed to be looking for a general method that would always work. I honestly can't think of anything that doesn't require ahead-of-time setup/knowledge, like "these are the only possible keys" or "this index has been created" or "this is how the data is stored on disc". I agree that different situations lend themselves to different approaches, not all of which are equally efficient. I think we can all agree on that.

We only have the original post as a reference; we don't know how the actual interview question was asked, or if the asker might have clarified their question with enough prodding. But if we take the original post at face value, then I'm not sure there's a general method that is actually better/more generally applicable than defaulting to a select list of one form or another. That's just my point of view though.

Thanks,

------------------------------
Tyrel Marak
Technical Support Manager
Aptron Corporation
Florham Park NJ US
------------------------------

Like

+4

Jonathan Smith
Rocketeer
Forum|Forum|2 years ago
May 25, 2023

Hi Scott:

It could also be someone who doesn't completely understand the internals and thought that if you did a simple LIST ... it's a way of reading records without an 'actual' SELECT. It could have also been referring to the FORMLIST Basic command to turn a dynamic array into 'select' list.

Did he ever provide an answer?

Sam

------------------------------
Samuel A Powell
President/Developer
Advanced Transportation Systems Inc
Colorado Springs CO US
------------------------------

@Samuel A Powell @Jon Kristofferson @Tyrel Marak @Ian McGowan It is possible to do it and I showed how in UniData yesterday but you might of missed the posts, so I suspect the guy asking the question did in fact know a lot about programming.

The simplist way I can think of without a SELECT statement. Create and Build an Index on the file using @ID (Try this in the demo account). Use the SETINDEX command to position the program at the first index key in the index and then use the READFWD command. READFWD also has READFWDU and READFWDL to lock records as well. BSCAN in UniVerse would allow you to follow a similar logic.

OPEN "CUSTOMER" TO F.CUSTOMER ELSE STOP
SETINDEX "@ID" ON F.CUSTOMER
EOF = @FALSE
LOOP
READFWD R.CUSTOMER FROM F.CUSTOMER ELSE EOF = @TRUE
UNTIL EOF DO
CRT @ID : " " : R.CUSTOMER
REPEAT
END

Regards,

------------------------------
Jonathan Smith
UniData ATS
Rocket Support
------------------------------

UniData ATS

Like

Ian McGowan
Participating Frequently
Forum|Forum|2 years ago
May 25, 2023

I finished my contract last week, so back on the market. I landed an interview with a "recognizable company" and went straight to the final round.

During the interview one of the panel asked me, "How do you read a file without a select list?" I paused for a moment wondering why anyone would need to do that? I thought for a moment and came to the conclusion, it may be possible, but I cannot think of how it could be done. I responded to him, "In the twenty years I've worked in multivalue, I have never seen any code that would do that. But I don't ever recall ever having the need".

Is it possible? Does anyone have an example?

Added: This person meant without using SELECT anywhere. At TCL or internally in a program. He claims he has a way, I doubt him.

------------------------------
Scott Johnston
Sr Software Engineer, Architect & Developer
Dover DE US
------------------------------

If you have a list of keys from some other source, or you know the structure of the keys (maybe they are ascending integers < 999,999), then you can read the records in without EXECUTE \\SELECT..\\, or GET.LIST or the SELECT command. Otherwise, we're going to need you to call them back and find out what their answer is :-) It seems like one of those interview gotcha questions to me - my money is on the Basic SELECT command, which I don't think of as creating a select list, but just traversing the file.

------------------------------
Ian McGowan
Principal Consultant
Rocket Forum Shared Account
------------------------------

Like

+1

Mike Rajkowski
Rocketeer
Forum|Forum|2 years ago
May 25, 2023

I finished my contract last week, so back on the market. I landed an interview with a "recognizable company" and went straight to the final round.

During the interview one of the panel asked me, "How do you read a file without a select list?" I paused for a moment wondering why anyone would need to do that? I thought for a moment and came to the conclusion, it may be possible, but I cannot think of how it could be done. I responded to him, "In the twenty years I've worked in multivalue, I have never seen any code that would do that. But I don't ever recall ever having the need".

Is it possible? Does anyone have an example?

Added: This person meant without using SELECT anywhere. At TCL or internally in a program. He claims he has a way, I doubt him.

------------------------------
Scott Johnston
Sr Software Engineer, Architect & Developer
Dover DE US
------------------------------

Scott,

There are several good answers on the thread, but I see the issue with the question. I believe you would need more information, to properly answer.

My first thought is what type of file?
We may assume the interviewer was discussing a MultiValue file, but in fact it could be sequential, where no SELECT is needed to read the entire file.
We know nothing about the keys, as suggested in another post, and if there is an ID counter used in the file, no select is needed.
Lastly, I agree with Jonathan, if there is an index on the id, setting the index, and reading through the file is a good method to avoid a large SELECT list, and is what I expect the interviewer is doing.

------------------------------
Mike Rajkowski
MultiValue Product Evangelist
Rocket Internal - All Brands
US
------------------------------

Like

L

Leslie Sherlock Hewkin
New Participant
Forum|Forum|2 years ago
May 26, 2023

Scott,

There are several good answers on the thread, but I see the issue with the question. I believe you would need more information, to properly answer.

My first thought is what type of file?
We may assume the interviewer was discussing a MultiValue file, but in fact it could be sequential, where no SELECT is needed to read the entire file.
We know nothing about the keys, as suggested in another post, and if there is an ID counter used in the file, no select is needed.
Lastly, I agree with Jonathan, if there is an index on the id, setting the index, and reading through the file is a good method to avoid a large SELECT list, and is what I expect the interviewer is doing.

------------------------------
Mike Rajkowski
MultiValue Product Evangelist
Rocket Internal - All Brands
US
------------------------------

Are over thinking things, a READ doesn't need a select, I wrote a lot of applications that didn't contain a single select. The other way is using READSEQ.

------------------------------
Leslie Sherlock Hewkin
Business Analyst
Rocket Forum Shared Account
------------------------------

Like

Will Johnson
Participating Frequently
Forum|Forum|2 years ago
May 26, 2023

I finished my contract last week, so back on the market. I landed an interview with a "recognizable company" and went straight to the final round.

During the interview one of the panel asked me, "How do you read a file without a select list?" I paused for a moment wondering why anyone would need to do that? I thought for a moment and came to the conclusion, it may be possible, but I cannot think of how it could be done. I responded to him, "In the twenty years I've worked in multivalue, I have never seen any code that would do that. But I don't ever recall ever having the need".

Is it possible? Does anyone have an example?

Added: This person meant without using SELECT anywhere. At TCL or internally in a program. He claims he has a way, I doubt him.

------------------------------
Scott Johnston
Sr Software Engineer, Architect & Developer
Dover DE US
------------------------------

You don't need to select a file to anything

OPEN N.FILE TO F.FILE ELSE dosomethingelse
SELECT F.FILE
READNEXT K.FILE

there is no select LIST created, the select only opens a pointer to the start of the file and the pointer is pointing to where it's traversing to next
no LIST at all

------------------------------
Will Johnson
Systems Analyst
Rocket Forum Shared Account
------------------------------

Like

+1

Mike Rajkowski
Rocketeer
Forum|Forum|2 years ago
May 26, 2023

You don't need to select a file to anything

OPEN N.FILE TO F.FILE ELSE dosomethingelse
SELECT F.FILE
READNEXT K.FILE

there is no select LIST created, the select only opens a pointer to the start of the file and the pointer is pointing to where it's traversing to next
no LIST at all

------------------------------
Will Johnson
Systems Analyst
Rocket Forum Shared Account
------------------------------

Will,

I believe that is a grey area, the documentation defines what is returned from the SELECT statement as a active select list of all record IDs in a file. Yet it also acts differently from the SELECT done at ECL/TCL, in that it processes one group at a time.

------------------------------
Mike Rajkowski
MultiValue Product Evangelist
Rocket Internal - All Brands
US
------------------------------

Like

Will Johnson
Participating Frequently
Forum|Forum|2 years ago
May 26, 2023

Will,

I believe that is a grey area, the documentation defines what is returned from the SELECT statement as a active select list of all record IDs in a file. Yet it also acts differently from the SELECT done at ECL/TCL, in that it processes one group at a time.

------------------------------
Mike Rajkowski
MultiValue Product Evangelist
Rocket Internal - All Brands
US
------------------------------

I will stipulate to the idea that it returns the first group. I personally found that out by accident, 30 years ago when I parsed the string returned. I didn't know it had been documented since then.

So yes this is a list, so I suppose I should modify my statement to say that there is a pointer to the frame start, and a text string of the first groups contents. Then when that group is exhausted, it triggers the pointer to move forward one group.

I still think this is what the interviewer was going for however.

------------------------------
Will Johnson
Systems Analyst
Rocket Forum Shared Account
------------------------------

Like

S

Shankar Bhagat
New Participant
Forum|Forum|1 year ago
July 25, 2024

I finished my contract last week, so back on the market. I landed an interview with a "recognizable company" and went straight to the final round.

During the interview one of the panel asked me, "How do you read a file without a select list?" I paused for a moment wondering why anyone would need to do that? I thought for a moment and came to the conclusion, it may be possible, but I cannot think of how it could be done. I responded to him, "In the twenty years I've worked in multivalue, I have never seen any code that would do that. But I don't ever recall ever having the need".

Is it possible? Does anyone have an example?

Added: This person meant without using SELECT anywhere. At TCL or internally in a program. He claims he has a way, I doubt him.

------------------------------
Scott Johnston
Sr Software Engineer, Architect & Developer
Dover DE US
------------------------------

Well I am new to this, but wouldn't this below do the job, tested ,it works.

0001: OPEN 'FILENAME' TO FILENAME ELSE STOP
0002: READV NAME FROM FILENAME,'RECORDID',2 ELSE NAME=""
0003: CRT NAME

------------------------------
Shankar Bhagat
Software developer
Rocket Forum Shared Account
------------------------------

Like

P

Phillip Potter
Participating Frequently
Forum|Forum|1 year ago
July 26, 2024

Well I am new to this, but wouldn't this below do the job, tested ,it works.

0001: OPEN 'FILENAME' TO FILENAME ELSE STOP
0002: READV NAME FROM FILENAME,'RECORDID',2 ELSE NAME=""
0003: CRT NAME

------------------------------
Shankar Bhagat
Software developer
Rocket Forum Shared Account
------------------------------

The problem makes sense only if he means "how does one read an _entire_ file w/o a select."

------------------------------
Phillip Potter
V.P. R&D
Data Management Associates Inc DMA
Cincinnati OH US
------------------------------

Like

Peter Gonzalez
Participating Frequently
Forum|Forum|1 year ago
July 26, 2024

Well I am new to this, but wouldn't this below do the job, tested ,it works.

0001: OPEN 'FILENAME' TO FILENAME ELSE STOP
0002: READV NAME FROM FILENAME,'RECORDID',2 ELSE NAME=""
0003: CRT NAME

------------------------------
Shankar Bhagat
Software developer
Rocket Forum Shared Account
------------------------------

Here is a simple program that does not use a SELECT. In order to READ records you have to have a datafile or a record.

Note: don't pay too much attention to the logic.

OPEN "PETER" TO F.PETER ELSE STOP (a DOS file with a name of 1 and with tab delimiters)
OPEN "CUSTOMER" TO F.CUSTOMER ELSE STOP
*
READ R.PETER FROM F.PETER, "1" ELSE R.PETER = ""
*
SWAP CHAR(09) WITH "|" IN R.PETER
R.PETER = TRIM(R.PETER)
CLASS.LIST = "999"
*
LOOP
REMOVE DLINE FROM R.PETER SETTING JUNK
IF JUNK # 2 THEN

CUSTOMER.ID = FIELD(DLINE,"|",1)
READ R.CUST FROM F.CUSTOMER, CUSTOMER.ID ELSE R.CUST = ""
R.CUST<10> = CLASS.LIST
WRITE R.CUST ON F.CUSTOMER, CUSTOMER.ID
END ELSE

EXIT

END
*
REPEAT

------------------------------
Peter Gonzalez
St. Louis, MO US
------------------------------

Like

Mark Baldridge
Participating Frequently
Forum|Forum|1 year ago
July 26, 2024

I finished my contract last week, so back on the market. I landed an interview with a "recognizable company" and went straight to the final round.

During the interview one of the panel asked me, "How do you read a file without a select list?" I paused for a moment wondering why anyone would need to do that? I thought for a moment and came to the conclusion, it may be possible, but I cannot think of how it could be done. I responded to him, "In the twenty years I've worked in multivalue, I have never seen any code that would do that. But I don't ever recall ever having the need".

Is it possible? Does anyone have an example?

Added: This person meant without using SELECT anywhere. At TCL or internally in a program. He claims he has a way, I doubt him.

------------------------------
Scott Johnston
Sr Software Engineer, Architect & Developer
Dover DE US
------------------------------

I like Jonathan's answer using READFWD as a great answer. UniVerse can read ID out of the Index using BSCAN. Strictly speaking, BUILD.INDEX uses a SELECT SAVING to produce a list of value / ID pairs to create the INDEX, so that might disqualify that answer. A brute force and requiring internals knowledge, involves READBLK and decoding the file structure to extract ID. Separating keys and data in UniData files might simplify that task.

Technically, The UniVerse (and now UniData) incremental BASIC select also does not produce a select list, per se, as it extracts ID group by group. The @SELECTED variable supports this idea by returning the number of records found in each group as it processes. In UniVerse, this is not quite true if the file is initially empty and subsequently loaded. At CREATE.INDEX time, the need-build flag is set to built if the file is empty (however, that is determined by scanning the file).

Otherwise, you might avoid a select if you have some knowledge of the ID that would permit inferring the ID in the file. An example would be a numerical key with known start and stop values. Additions can increment the stop value and deletions can increment the start value, assuming deletions remove the smallest value. This technique can appear in a file-based job queue.

------------------------------
Mark A Baldridge
Principal Consultant
Thought Mirror
Nacogdoches, Texas United States
------------------------------

Like

Will Johnson
Participating Frequently
Forum|Forum|1 year ago
July 26, 2024

I finished my contract last week, so back on the market. I landed an interview with a "recognizable company" and went straight to the final round.

During the interview one of the panel asked me, "How do you read a file without a select list?" I paused for a moment wondering why anyone would need to do that? I thought for a moment and came to the conclusion, it may be possible, but I cannot think of how it could be done. I responded to him, "In the twenty years I've worked in multivalue, I have never seen any code that would do that. But I don't ever recall ever having the need".

Is it possible? Does anyone have an example?

Added: This person meant without using SELECT anywhere. At TCL or internally in a program. He claims he has a way, I doubt him.

------------------------------
Scott Johnston
Sr Software Engineer, Architect & Developer
Dover DE US
------------------------------

I will address, just the last part, the need.

I do have a case. Several times in my career I have been asked to, for example, "look for any TABs that might have gotten accidentally data-entered into this file" (Just one example)

In that case you don't need to select the file in any particular order, because you are going to traverse the entire file. So you can just open the file and do the SELECT which only opens the first group of the file and start traversing with Readnext.

I do remember someone stating that the basic SELECT has been modified to select ALL ids in the file, I don't think that could be possible. We have file with millions of ids in them and yet the readnext starts churning through them right away.

------------------------------
Will Johnson
Systems Analyst
Rocket Forum Shared Account
------------------------------

Like

Mark Baldridge
Participating Frequently
Forum|Forum|1 year ago
July 26, 2024

I will address, just the last part, the need.

I do have a case. Several times in my career I have been asked to, for example, "look for any TABs that might have gotten accidentally data-entered into this file" (Just one example)

In that case you don't need to select the file in any particular order, because you are going to traverse the entire file. So you can just open the file and do the SELECT which only opens the first group of the file and start traversing with Readnext.

I do remember someone stating that the basic SELECT has been modified to select ALL ids in the file, I don't think that could be possible. We have file with millions of ids in them and yet the readnext starts churning through them right away.

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Will Johnson
Systems Analyst
Rocket Forum Shared Account
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In UniVerse, you can use the SEARCH command, and enter a TAB at the prompt. It will return a list of all ID whose record contains at least one TAB character. The SEARCH command dispatch character is a Q, so it is a query command, but not exactly a SELECT,

A large list of ID end up in UVTEMP.

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Mark A Baldridge
Principal Consultant
Thought Mirror
Nacogdoches, Texas United States
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Will Johnson
Participating Frequently
Forum|Forum|1 year ago
July 26, 2024

In UniVerse, you can use the SEARCH command, and enter a TAB at the prompt. It will return a list of all ID whose record contains at least one TAB character. The SEARCH command dispatch character is a Q, so it is a query command, but not exactly a SELECT,

A large list of ID end up in UVTEMP.

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Mark A Baldridge
Principal Consultant
Thought Mirror
Nacogdoches, Texas United States
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Yes sure there may be other ways to do the specific example I mentioned, however you have to remember that I have worked on all different Pick systems, not just Universe, and over the past forty years. This was just one example, where you would need to traverse an entire file and do not need it sorted in any particular order.

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Will Johnson
Systems Analyst
Rocket Forum Shared Account
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Joe Goldthwaite
Participating Frequently
Forum|Forum|1 year ago
July 26, 2024

I finished my contract last week, so back on the market. I landed an interview with a "recognizable company" and went straight to the final round.

During the interview one of the panel asked me, "How do you read a file without a select list?" I paused for a moment wondering why anyone would need to do that? I thought for a moment and came to the conclusion, it may be possible, but I cannot think of how it could be done. I responded to him, "In the twenty years I've worked in multivalue, I have never seen any code that would do that. But I don't ever recall ever having the need".

Is it possible? Does anyone have an example?

Added: This person meant without using SELECT anywhere. At TCL or internally in a program. He claims he has a way, I doubt him.

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Scott Johnston
Sr Software Engineer, Architect & Developer
Dover DE US
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I'm curious to find out your interviewer's solution. All the read statements require an ID so you have get it from somewhere. As other people have mentioned, SELECT file.variable doesn't built a list. It just keeps a pointer in the file and processes items in their hashed order. Technically that's not doing a select so maybe that's what he was talking about?

You can use OPENSEQ and READSEQ to process non-database without a select but that doesn't work with hashed files.

Maybe he was talking about Johnathan's READFWD method. I had never heard of it but it looks like it's new to Universe 12 and I'm working in Universe 11. Maybe it's in other implementations but if it is, Google doesn't seem to know about it.

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Joe Goldthwaite
Consultant
Phoenix AZ US
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Peter Cheney
Participating Frequently
Forum|Forum|1 year ago
July 28, 2024

I finished my contract last week, so back on the market. I landed an interview with a "recognizable company" and went straight to the final round.

During the interview one of the panel asked me, "How do you read a file without a select list?" I paused for a moment wondering why anyone would need to do that? I thought for a moment and came to the conclusion, it may be possible, but I cannot think of how it could be done. I responded to him, "In the twenty years I've worked in multivalue, I have never seen any code that would do that. But I don't ever recall ever having the need".

Is it possible? Does anyone have an example?

Added: This person meant without using SELECT anywhere. At TCL or internally in a program. He claims he has a way, I doubt him.

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Scott Johnston
Sr Software Engineer, Architect & Developer
Dover DE US
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If the record id's conform to some sort of schema then it ought to be possible to create them on the fly inside a loop?

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Peter Cheney
Software Superstar
Firstmac
Brisbane Qld Australia
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Stuart Boydell
Participating Frequently
Forum|Forum|1 year ago
July 28, 2024

I finished my contract last week, so back on the market. I landed an interview with a "recognizable company" and went straight to the final round.

During the interview one of the panel asked me, "How do you read a file without a select list?" I paused for a moment wondering why anyone would need to do that? I thought for a moment and came to the conclusion, it may be possible, but I cannot think of how it could be done. I responded to him, "In the twenty years I've worked in multivalue, I have never seen any code that would do that. But I don't ever recall ever having the need".

Is it possible? Does anyone have an example?

Added: This person meant without using SELECT anywhere. At TCL or internally in a program. He claims he has a way, I doubt him.

------------------------------
Scott Johnston
Sr Software Engineer, Architect & Developer
Dover DE US
------------------------------

My answer would be unless there's a significant use case for not using a SELECT I wouldn't attempt to write something so non-standard that the collective group of wise heads here can't figure it out :) It sounds like a recipe for support nightmares.

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Stuart Boydell
Technical Specialist
Meier Business Systems PTY LTD
Carnegie Vic AU
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