autoincrement vs uniqueidentifier (easy)

[yui]

Hi there,

I need to create unique primary keys in my tables but I don't care about the
format of these keys. They're used simply to identify the record and serve
as foreign keys in other tables (users never see them). I've always relied
on autoincrement keys for this in the past (normally stored as integers) but
now I see SQL Server has a "uniqueidentifier" type which is just a GUID by
default (apparently you can change this though). It's been a long time since
I've done any SQL Server programming so:

1) How exactly would I create an integer field that serves as an
autoincrement key (what do I set in VS which is where I'm managing my DB for
now)
2) Why would (or should) I use a "uniqueidentifier" instead of 1 above. If
an autoincrement key is incremented for each new record and will never be
reused (and my tables will never approach 2+ billion records), what's the
point of a "uniqueidentifier" in this case (if any). It just takes up extra
space and buys me nothing in return (compared to the smaller 32 bit integer)

Thanks in advance.

 

[Gregory A. Beamer]

Hi there,

I need to create unique primary keys in my tables but I don't care
about the format of these keys. They're used simply to identify the
record and serve as foreign keys in other tables (users never see
them). I've always relied on autoincrement keys for this in the past
(normally stored as integers) but now I see SQL Server has a
"uniqueidentifier" type which is just a GUID by default (apparently
you can change this though). It's been a long time since I've done any
SQL Server programming so:

1) How exactly would I create an integer field that serves as an
autoincrement key (what do I set in VS which is where I'm managing my
DB for now)

CREATE TABLE Table1
(
Table1ID int IDENTITY(1,1) PRIMARY KEY
)

2) Why would (or should) I use a "uniqueidentifier" instead of 1
above. If an autoincrement key is incremented for each new record and
will never be reused (and my tables will never approach 2+ billion
records), what's the point of a "uniqueidentifier" in this case (if
any). It just takes up extra space and buys me nothing in return
(compared to the smaller 32 bit integer)

If the database is spread over many servers, the GUID makes more sense, as
it is statistically guaranteed to be unique.

If you have clients that are detatched and can create new records, the GUID
makes more sense.

Peace and Grace,

 

[DDD]

Hi there,

I need to create unique primary keys in my tables but I don't care about the
format of these keys. They're used simply to identify the record and serve
as foreign keys in other tables (users never see them). I've always relied
on autoincrement keys for this in the past (normally stored as integers) but
now I see SQL Server has a "uniqueidentifier" type which is just a GUID by
default (apparently you can change this though). It's been a long time since
I've done any SQL Server programming so:

1) How exactly would I create an integer field that serves as an
autoincrement key (what do I set in VS which is where I'm managing my DB for
now)

You wanna create the field in codes? in GUI?

2) Why would (or should) I use a "uniqueidentifier" instead of 1 above. If
an autoincrement key is incremented for each new record and will never be
reused (and my tables will never approach 2+ billion records), what's the
point of a "uniqueidentifier" in this case (if any). It just takes up extra
space and buys me nothing in return (compared to the smaller 32 bit integer)

In my opinion, an autoincrement key will be a bottleneck if there are
many requests at the same time.
Because the key has to be added in order. GUID has no this problem,
there is no relations between two GUID number.

Thanks in advance.

Good luck.


Maybe contain nuts.

 

[--CELKO--]

I need to create unique primary keys [what other kind are there in your world?] in my tables but I don't care about the format of these keys. <<

You have no idea what a key is at all. It is a subset of the
attrbutes of an entity that uniquely identify each occurence of the
entity. You should care very much about it

They're used simply to identify the record [rows are not records] and serve as foreign keys in other tables (users never see them).<<

That is an exposed physical locator. It is like a 1950's pointer
chain; you (the user) have to maintain it manually and it has nothing
whatsoever to do with the logical data model. It lets you avoid
learning RDBMS at the expense of data integrity.

I've always relied on autoincrement keys [sic] for this in the past (normally stored as integers) but now I see SQL Server has a "uniqueidentifier" type which is just a GUID by default (apparently you can change this though).<<

autoincrements look just like record numbering on a magantic tape
file, so you can stay in your comfort zone.

No, it sounds like you have been doing 1950's COBOL file sytrem
programming with T-SQL and have never actually written a proper
schema. Get a book on basics and read it. Look at most of the
posters in the newsgroups. They do not post DDL -- often because they
have no idea what it is -- and invent their own pseudo-code. They
have no idea what a spec is, but post requests for ways to implement
an approach they have locked into -- and it is usually a non-
relational approach at that.

What we have are some really lazy programmers who want to use the
newsgroups to do their job or homework for them. Even worse, they
want to get an instant college education which is not possible in a
short reply. The questions they ask can most often be answered by (1)
RTFM, well BOL (2) "Try it and see" (3) a quick Google search in the
newsgroup to which they are posting.

What they get instead from most replies is a kludge to get rid of
them. If this was a woodworking newsgroup and someone posted "What is
the best kind of rocks to pound screws into fine furniture?" are you
really helping them when you say "Granite! Use big hunks of granite!"
I am the guy who replies with "Your question is bad. Don't you know
about screwdrivers?" And I like to remind them that it takes six
years to become a Journeyman Union Carpenter in New York State. Not
Master, Journeyman.

 

[Erland Sommarskog]

2) Why would (or should) I use a "uniqueidentifier" instead of 1 above.
If an autoincrement key is incremented for each new record and will
never be reused (and my tables will never approach 2+ billion records),
what's the point of a "uniqueidentifier" in this case (if any). It just
takes up extra space and buys me nothing in return (compared to the
smaller 32 bit integer)

One possibly advantage with GUIDS is that these can be generated client-
side, and you don't have to make a round-trip to get the value. This can
make things easier if you need to insert, say, both Orders and OrderDetails.

On the other hand a GUID is 16 bytes, four times an integer. GUIDs can
also lead to performance problems with fragmentation if you don't deal
with them correctly.

In short, as long you don't have any problems with integer keys, stick to
them, and only use GUIDs if you find that you actually need to.


--
Erland Sommarskog, SQL Server MVP, (e-mail address removed)

Links for SQL Server Books Online:
SQL 2008: http://msdn.microsoft.com/en-us/sqlserver/cc514207.aspx
SQL 2005: http://msdn.microsoft.com/en-us/sqlserver/bb895970.aspx
SQL 2000: http://www.microsoft.com/sql/prodinfo/previousversions/books.mspx

 

[Guest]

2) Why would (or should) I use a "uniqueidentifier" instead of 1 above. If
an autoincrement key is incremented for each new record and will never be
reused (and my tables will never approach 2+ billion records), what's the
point of a "uniqueidentifier" in this case (if any). It just takes up extra
space and buys me nothing in return (compared to the smaller 32 bit integer)

"uniqueidentifier" field can help to keep id "secret"

e.g. when you have

site.com/userprofile.aspx?id=100
site.com/userprofile.aspx?id=101
site.com/userprofile.aspx?id=102

then everyone knows how many items you have because of 100, 101, 102

This

site.com/userprofile.aspx?id=6F9619FF-8B86-D011-B42D-00C04FC964FF

comes in handy if you like to hide that information.

As from the database point of view, uniqueidentifier is useful if
you're consolidating records from multiple databases into one table.
On another hand, uniqueidentifier has long values, uses more space and
it is recommended to use the IDENTITY when global uniqueness is not
required, or when having a serially incrementing key is preferred.

 

[yui]

CREATE TABLE Table1
(
Table1ID int IDENTITY(1,1) PRIMARY KEY

Thanks. I should be able to (now) find the equivalent in VS itself.

If the database is spread over many servers, the GUID makes more sense, as
it is statistically guaranteed to be unique.

That's a good reason but not applicable in my case

If you have clients that are detatched and can create new records, the
GUID
makes more sense.

Also N/A.

Thanks for your help!

 

[yui]

1) How exactly would I create an integer field that serves as an
autoincrement key (what do I set in VS which is where I'm managing my DB
for
now)

You wanna create the field in codes? in GUI?

GUI. The tables are statically created and the schema never changes.

In my opinion, an autoincrement key will be a bottleneck if there are
many requests at the same time.
Because the key has to be added in order. GUID has no this problem,
there is no relations between two GUID number.

I'd have to check that. Perhaps you're right but I honestly have my doubts
(about any noticeable performance hit). GUIDs would appear to be worse since
they're longer and are more time-consuming to generate

Thanks for your help.

 

[yui]

On the other hand a GUID is 16 bytes, four times an integer. GUIDs can
also lead to performance problems with fragmentation if you don't deal
with them correctly.

Can you elaborate on "don't deal with them correctly". What control do you
have over fragmentation without defragmenting the DB itself (during some
maintenance period in most cases)

In short, as long you don't have any problems with integer keys, stick to
them, and only use GUIDs if you find that you actually need to.

This is how I see it. Thanks for your insight.

 

[yui]

"uniqueidentifier" field can help to keep id "secret"

e.g. when you have
site.com/userprofile.aspx?id=100
site.com/userprofile.aspx?id=101
site.com/userprofile.aspx?id=102
then everyone knows how many items you have because of 100, 101, 102
site.com/userprofile.aspx?id=6F9619FF-8B86-D011-B42D-00C04FC964FF
comes in handy if you like to hide that information.

That's a good point though not applicable in my case (but useful to consider
for next time)

As from the database point of view, uniqueidentifier is useful if
you're consolidating records from multiple databases into one table.
On another hand, uniqueidentifier has long values, uses more space and
it is recommended to use the IDENTITY when global uniqueness is not
required, or when having a serially incrementing key is preferred.

Merging DBs isn't an issue in my case but if it's occuring during some
maintenance period only, integer keys can easily be resequenced. The issue
only becomes significant IMO when dealing with a distributed DB system whose
keys must be kept unique at all times (which is what you're probably
alluding to). Based on your input and others, I should be ok with
autoincrement (integer) keys. Thanks for your feedback.

 

[Guest]

That's a good point though not applicable in my case (but useful to consider
for next time)


Merging DBs isn't an issue in my case but if it's occuring during some
maintenance period only, integer keys can easily be resequenced. The issue
only becomes significant IMO when dealing with a distributed DB system whose
keys must be kept unique at all times (which is what you're probably
alluding to). Based on your input and others, I should be ok with
autoincrement (integer) keys. Thanks for your feedback.

Glad to help

 

[Erland Sommarskog]

Can you elaborate on "don't deal with them correctly". What control do you
have over fragmentation without defragmenting the DB itself (during some
maintenance period in most cases)

A good start is to not make the index on the GUID column clustered.

If you make it clustered, you should give it a low fillfactor, 30-50%.
When new rows will be added in the gaps, and there will be no page splits,
until you start to fill up the gaps. Then it's time for an index rebuild
with a low fillfactor again.

An index on GUIDs with a default fillfactor will see lots of page splits,
which leads to poor INSERT performance and also fragmentation.


--
Erland Sommarskog, SQL Server MVP, (e-mail address removed)

Links for SQL Server Books Online:
SQL 2008: http://msdn.microsoft.com/en-us/sqlserver/cc514207.aspx
SQL 2005: http://msdn.microsoft.com/en-us/sqlserver/bb895970.aspx
SQL 2000: http://www.microsoft.com/sql/prodinfo/previousversions/books.mspx

 

[yui]

On the other hand a GUID is 16 bytes, four times an integer. GUIDs can

A good start is to not make the index on the GUID column clustered.

If you make it clustered, you should give it a low fillfactor, 30-50%.
When new rows will be added in the gaps, and there will be no page splits,
until you start to fill up the gaps. Then it's time for an index rebuild
with a low fillfactor again.

An index on GUIDs with a default fillfactor will see lots of page splits,
which leads to poor INSERT performance and also fragmentation.

Thanks for the info. It's something worth investigating (to reduce
fragmention in general) but I'll be sticking with integer keys in any case.
It serves my purpose. Thanks again.

 

[Erland Sommarskog]

Thanks for the info. It's something worth investigating (to reduce
fragmention in general) but I'll be sticking with integer keys in any
case. It serves my purpose. Thanks again.

Just to make it clear: the stuff with fillfactor etc that I discussed
pertains to GUIDs. If you use monotonically integer keys, there will
not be issues with pages splits etc as you would get with GUIDs.


--
Erland Sommarskog, SQL Server MVP, (e-mail address removed)

Links for SQL Server Books Online:
SQL 2008: http://msdn.microsoft.com/en-us/sqlserver/cc514207.aspx
SQL 2005: http://msdn.microsoft.com/en-us/sqlserver/bb895970.aspx
SQL 2000: http://www.microsoft.com/sql/prodinfo/previousversions/books.mspx

 

[Gregory A. Beamer]

Thanks. I should be able to (now) find the equivalent in VS itself.

THe designer in VS, which I have not used much, should allow you to click
the Identity field and set the seed and increment (defaulted to 1 and 1).
If you have any issues, the tool that comes with SQL Express has a table
designer that will have everything you need to design the table properly.
If you are using SQL Server proper (developer, standard, enterprise), the
tools are even better.

 

[yui]

Just to make it clear: the stuff with fillfactor etc that I discussed
pertains to GUIDs. If you use monotonically integer keys, there will
not be issues with pages splits etc as you would get with GUIDs.

Ok, thanks. I didn't actually jump to any conslusions about what it impacts
exactly (in spite of my wording) but I know I need to read up on it first.
Thanks again.

 

[yui]

THe designer in VS, which I have not used much, should allow you to click
the Identity field and set the seed and increment (defaulted to 1 and 1).

That's what I would have thought but I didn't see any such thing when I went
into the column's properties (in Server Explorer). It does exist for the
column's properties if you create a "DataSet", drag a table onto it in the
VS designer, and then inspect the column's properties there. I'll have to
experiment however to see exactly what changes in the "DataSet" are
propagated back to the DB itself (if any)

If you have any issues, the tool that comes with SQL Express has a table
designer that will have everything you need to design the table properly.
If you are using SQL Server proper (developer, standard, enterprise), the
tools are even better.

No doubt but since my needs are relatively simple, I was doing this in IDE
(one stop and shop). Do you know if any of those tools plug into VS itself
(as an AddIn). The ones in VS are somtimes unwieldy and sluggish (as well as
incomplete). Thanks for your help.

 

[deric]

man you're a jerk. i just got a computer science degree and find the
original question informed, logical, and appropriate.