Downside Of Multiple Primary Keys
Oct 11, 2006
Hi, from the "best practice" perspective, how convenient is to use multiple field primary keys in a table, how convenient is it to replace a multifield pk with an autoincrement field to represent such a table?
I tried using a calculated field product of appending the fields that cvompose the primary key, but MySQL for example, does not provide with that functionality, which makes me wonder it doing so in SQL Server is a good practice at all.
Thank you
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Jun 18, 2008
Hi Guys,
Can someone tell me what is the best way to check 2 tables lets say tb1 and tb2, to find those customers that are in tb1 but not in tb2 using four fields(cardno,spend,date,refno) as the primary key. Duplicates fields are in tb1
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Aug 13, 2007
Hi,
I have recently been looking at a database and wondered if anyone can tell me what the advantages are supporting a unique collumn, which can essentially be seen as the primary key, with an identity seed integer primary key.
For example:
id [unique integer auto incremented primary key - not null],
ClientCode [unique index varchar - not null],
name [varchar null],
surname [varchar null]
isn't it just better to use ClientCode as the primary key straight of because when one references the above table, it can be done easier with the ClientCode since you dont have to do a lookup on the ClientCode everytime.
Regards
Mike
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Feb 1, 2007
Hi,
I am trying to execute following sql script in sql-server 2000 query analyzer
CREATE TABLE user_courses (user_id varchar(30) NOT NULL PRIMARY KEY,
course_id varchar(10) NOT NULL PRIMARY KEY)
Its give's me following error :-
Cannot specify multiple primary key constraint
Hence I am not able to ceate table with multiple primary keys. So can any one tell me how to get this done?.
Secondly, Primary key must be unique i.e duplicate values are not allowed in P.K field. But in this case since I am declaring two fileds as primary keys.
Will it allow me to have following records in the user_courses table?
user_id(P.K) course_id(P.K)
bob CRS235
alice CRS235
Tim CRS235
tom CRS635
So, if we consider both the fields as primary keys together than I am not voilating Uniqueness constraint. But, if I look at course_id alone then I am voilating uniqeness property?
Thanks,
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Mar 31, 2008
I have a database in XML format , with 100+ tables, that I want to import into SQL server but the problem is that I don't have any of the original primary key information. I know that some of the tables had multiple primary keys.
Is there a method or a tool that is capable of determining the primary keys for me??
I don't want to have to figure it out by hand, especially if I have more of these databases in the future.
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Apr 11, 2006
Hello again,
I'm going through my tables and rewriting them so that I can create relationship-based constraints and create foreign keys among my tables. I didn't have a problem with a few of the tables but I seem to have come across a slightly confusing hiccup.
Here's the query for my Classes table:
Code:
CREATE TABLE Classes
(
class_id
INT
IDENTITY
PRIMARY KEY
NOT NULL,
teacher_id
INT
NOT NULL,
class_title
VARCHAR(50)
NOT NULL,
class_grade
SMALLINT
NOT NULL
DEFAULT 6,
class_tardies
SMALLINT
NOT NULL
DEFAULT 0,
class_absences
SMALLINT
NOT NULL
DEFAULT 0,
CONSTRAINT Teacher_instructs_ClassFKIndex1 FOREIGN KEY (teacher_id)
REFERENCES Users (user_id)
)
This statement runs without problems and I Create the relationship with my Users table just fine, having renamed it to teacher_id. I have a 1:n relationship between users and tables AND an n:m relationship because a user can be a student or a teacher, the difference is one field, user_type, which denotes what type of user a person is. In any case, the relationship that's 1:n from users to classes is that of the teacher instructing the class. The problem exists when I run my query for the intermediary table between the class and the gradebook:
Code:
CREATE TABLE Classes_have_Grades
(
class_id
INT
PRIMARY KEY
NOT NULL,
teacher_id
INT
NOT NULL,
grade_id
INT
NOT NULL,
CONSTRAINT Grades_for_ClassesFKIndex1 FOREIGN KEY (grade_id)
REFERENCES Grades (grade_id),
CONSTRAINT Classes_have_gradesFKIndex2 FOREIGN KEY (class_id, teacher_id)
REFERENCES Classes (class_id, teacher_id)
)
Query Analyzer spits out: Quote: Originally Posted by Query Analyzer There are no primary or candidate keys in the referenced table 'Classes' that match the referencing column list in the foreign key 'Classes_have_gradesFKIndex2'. Now, I know in SQL Server 2000 you can only have one primary key. Does that mean I can have a multi-columned Primary key (which is in fact what I would like) or does that mean that just one field can be a primary key and that a table can have only the one primary key?
In addition, what is a "candidate" key? Will making the other fields "Candidate" keys solve my problem?
Thank you for your assistance.
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Jul 16, 2014
what the best practice is for creating indexes on columns that are foreign keys to the primary keys of other tables. For example:
[Schools] [Students]
---------------- -----------------
| SchoolId PK|<-. | StudentId PK|
| SchoolName | '--| SchoolId |
---------------- | StudentName |
-----------------
The foreign key above is as:
ALTER TABLE [Students] WITH CHECK ADD CONSTRAINT [FK_Students_Schools]
FOREIGN KEY([SchoolId]) REFERENCES [Schools] ([SchoolId])
What kind of index would ensure best performance for INSERTs/UPDATEs, so that SQL Server can most efficiently check the FK constraints? Would it be simply:
CREATE INDEX IX_Students_SchlId ON Students (SchoolId)
Or
CREATE INDEX IX_Students_SchlId ON Students (SchoolId, StudentId)
In other words, what's best practice for adding an index which best supports a Foreign Key constraint?
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May 16, 2008
Pls let me know How I generate script for All primary keys and foreign keys in a table. Thereafter that can be used to add primary keys and foreign keys in another databse with same structure.
Also how I script default and other constraints of a table?
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Jul 15, 2002
Can somebody explain to me how to best do inserts where you have primary keys and foreign keys.l'm battling.
Is there an article on primary keys/Pk ?
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Nov 15, 2006
"Violation of PRIMARY KEY of restriction 'PK_Approve_Overtime'. The overlapping key cannot be inserted in object 'Dbo.Approve_Overtime'. The statement was ended."
can soemone explain to me why i have this kind of error?
i have this two tables. approve_overtime table has a primary key id_no and application_input table with a primary key of id_no!
all the values from of application_input will be stored also in approve_overtime.
sometimes the datas can be stored.sometimes it cannot and produces an error!
what do u think?
hmmm pls help!
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May 16, 2002
Using SQL Svr 7.0. It appears that primary keys are created as nonclustered
unique indexes. Is there a configuration setting I can use to make them be
created as clustered unique indexes?
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Apr 4, 2001
If a table has a column defined as Int, Identity(1,1) which is to be used as the primary key, should that index be defined as clustered or non-clustered? In Enterprise manager when you create a PK on a table it defaults to being a clustered index. I am sure the answer depends on the other index requirements and columns in the table but I'd like to see what other ppl think about this.
Thanks!
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Mar 14, 2000
I have read that SQL Server tables can't have more than one primary key. I know in Access two keys are allowed. Why can't there be two primary keys in a single table in SQL Server 7.
Thanks
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Jun 15, 2004
Hi everyone,
Does someone knows how can I drop a primary key (that I don't know the name) from a table in one sql statement.
Thanks,
Fady
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Feb 19, 2004
HI ,
I accidently removed the primary keys from my table by mistake. Is there anyway ,That i can get the PK's back to what is used to be. Need Help pls...... When I try "resetting" the PK I kep getting this error:
'table_name' table
- Unable to create index 'PK_tablename'.
ODBC error: [Microsoft][ODBC SQL Server Driver][SQL Server]CREATE UNIQUE INDEX terminated because a duplicate key was found for index ID 1. Most significant primary key is '1'.
[Microsoft][ODBC SQL Server Driver][SQL Server]Could not create constraint. See previous errors.
[Microsoft][ODBC SQL Server Driver][SQL Server]Warning: The table 'tDetail' has been created but its maximum row size (12521) exceeds the maximum number of bytes per row (8060). INSERT or UPDATE of a row in this table will fail if the resulting row length exceeds 8060 bytes.
[Microsoft][ODBC SQL Server Driver][SQL Server]The statement has been terminated.
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May 17, 2004
In access you can have two fields that are primary keys with one or the other repeating as long as the combination is not repeated.
i.e.
key1 key2
200410 12345
200410 12346
200410 12588
etc for all 200410 there can not be a repeat of any value of key 2
is there a way to have this dual key in MSSQL :confused:
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Feb 13, 2006
Hi
How can 2 columns be clubbed together to form a primary key , i mean I have 2 columns job & Batch , need to club them together to form the primary key
How is it done I mean in the design , how to define that both the columns togethter form a primary key ,
Cause when I go to the table , it allows me to create a PK through the EM only for one column
Please help
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Oct 17, 2007
Hi there,
is there any way I can use INSERT so if I try to copy duplicate primary key data, it automatically skips the task and moves on to the next data?
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May 15, 2008
I have declared a table with a single column to be a Primary key. If I write 2 records, the first comprsing "A" and the second "a" then I get an exception about violating the uniqueness of the key. Is there a way that I can define the key to be case sensitive.
Many thanks
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May 4, 2007
I have two tables with similar primary keys, table a and table b, and I want to find out all the key values that are disimilar between the tables. Can this be done with a select? if so what would it be.
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Dec 29, 2007
I am not entirly sure what a forigen key is, is it a unique ID which is the same as the primary key? If adding a foreign key to a table that already has data, will it update each row with a unique ID or will it only create a unique ID on newly inserted records (for the foreign key)? If the foreign key is the same as the primary key then why do we need to even add a foreign key at all?For example a table like: Table Name : Customers--CustomerID uniqueidentity (primary Key)--FirstName nchar Table Name : Orders --OrderID int--CustomerID int Obviuously CustomerID are going to be the same in both tables, so why would you need to add a foreign key on 'CustomerID' to the 'Order' table, can't SQL match the customerID in each table any way? Cheers
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Mar 20, 2008
HiI have a database and I been inserting some dummy data into it but now I want to upload it to my website but I want to delete all the dummy data and start the PK back at 1. I truancted all the data but it still keeps counting from the last one.So how do I reset it?
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May 15, 2001
Hi,
I have a question on pk?
I have a db which has tables which do not have pk?I want to create Pk on each one of them - infact,I want to alter the table , add one more field and make it the pk .
My question is - do I will have to go to each table,alter it and then create the pk on it or do someone have any script or better way to do it?
Any help is appreciated.
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May 17, 2001
Hi,
Just a continuation to my earlier queries on replication.
I have a db which I want to replicate - it do not have pk?
I do not want to create pk on existing columns - so I thought of creating one more column in all the tables and make them pk .
Any one has any idea if this will work fine or may give any problem which I should be prepare for.
Any thought appreciated -
pvd
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May 6, 2005
I have a 3rd party app which had a primary key with about 5 fields. The last field of this was a trantype. This app had a posting process which uses this in it's sql. Ran rather slow. We added an individual index to this field and cut processing down 90%. It almost seemded like sl server was ignoring this index. Is this because it was the last field in the primary key index?
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Sep 10, 1998
Hi All,
I`m using BCP to import ASCII data text into a table that already has many records. BCP failed because of `Duplicate primary key`.
Now, is there any way using BCP to know precisely which record whose primary key caused that `violation of inserting duplicate key`.
I already used the option -O to output error to a `error.log`, but it doesn`t help much, because that error log contains the same error message mentioned above without telling me exactly which record so that I can pull that `duplicate record` out of my import data file.
TIA and you have a great day.
David Nguyen.
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Jun 25, 2002
Newbie question...
I have two tables (categories & listings) which create a many-to-many relationship.
I have created an interim table with the primary keys from each table as a composite primary key...(cat_id & list_id).
How does the interim table get populated with the id's?
When I do an insert statement to insert data into the categories table, the cat_id field is automatically generated...same with the listings table, but when (and how) does the primary key data get into the interim table.
Thanks in advance for the assistance.
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Jun 24, 2004
HI Folks ,
I have a problem with the primary keys in my main Db , I want to setup replication and looks like someone tampered with my database by removing the primary keys.and in order to setup replication i need this table to have primary keys .THere are duplicates in that table but they are nessecary...and for this reason the primary keys do not want to "stick" when i try and specify them.Can anybody help
Burner
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Jun 1, 2006
Hi all,
As our DB has no primary keys or indexes ive taken a copy of all populated tables and tried to force primary keys within a new DB.
the problem is all off the tables have multiple datasets within them, a dataset for each year. This causes all instances of ID numbers to not be unique as they are replicated for every year they are active.
Its a school database so a student who has been here for 3 years will have 3 instances of his ID number, one for each years' data set.
So how do i force primary keys if there is no unique identifier? ive been highlighting both data set and ID columns and setting that combination as the primary key.
Essentially i need to analyse the relationships between the tabls in a diagram and also run some speed tests to see how fast the db works when it has indexes and primary keys.
the reason im writing is that ive done this on ten tables and with another 160 to do im just checking im doing the right thing?
greg
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Jul 23, 2005
I'm working on a system that is very address-centric and detection ofduplicate addresses is very important. As a result we have brokenaddresses down into many parts (DDL below, but I've left out somereference tables for conciseness), these being state, locality, street,street number, and address. The breakdown is roughly consistent withAustralian addressing standards, we're working on finalising this.Because we carry the primary key down each of the levels, this hasresulted in our address table having a very wide primary key (around170 characters). We refer to addresses from a number of other tablesand although my instinct is to use this natural key in the other tablesI wonder if we should just put a unique index on the natural key,create a surrogate primary key and use it in the other table. Anythoughts?CREATE TABLE dbo.States (StateID varchar (3) NOT NULL ,StateName varchar (50) NOT NULL ,CONSTRAINT PK_AddressStates PRIMARY KEY NONCLUSTERED(StateID))CREATE TABLE dbo.Localities (Locality varchar (46) NOT NULL ,StateID varchar (3) NOT NULL ,Postcode char (4) NOT NULL ,CONSTRAINT PK_Localities PRIMARY KEY NONCLUSTERED(Locality,StateID,Postcode),CONSTRAINT FK_AddressLocalities_AddressStates FOREIGN KEY(StateID) REFERENCES dbo.States (StateID))CREATE TABLE dbo.Streets (StreetName varchar (35) NOT NULL ,StreetTypeID varchar (10) NOT NULL ,StreetDirectionID varchar (2) NOT NULL ,Locality varchar (46) NOT NULL ,StateID varchar (3) NOT NULL ,Postcode char (4) NOT NULL ,CONSTRAINT PK_Streets PRIMARY KEY CLUSTERED(StreetName,StreetTypeID,StreetDirectionID,Locality,StateID,Postcode),CONSTRAINT FK_Streets_Localities FOREIGN KEY(Postcode,Locality,StateID) REFERENCES dbo.Localities (Postcode,Locality,StateID))CREATE TABLE dbo.StreetNumbers (StreetName varchar (35) NOT NULL ,StreetTypeID varchar (10) NOT NULL ,StreetDirectionID varchar (2) NOT NULL ,Locality varchar (46) NOT NULL ,StateID varchar (3) NOT NULL ,Postcode char (4) NOT NULL ,StreetNumber varchar (15) NOT NULL ,BuildingName varchar (100) NOT NULL ,CONSTRAINT PK_StreetNumbers PRIMARY KEY CLUSTERED(StreetName,StreetTypeID,StreetDirectionID,Locality,StateID,Postcode,StreetNumber),CONSTRAINT FK_StreetNumbers_Streets FOREIGN KEY(StreetName,StreetTypeID,StreetDirectionID,Locality,StateID,Postcode) REFERENCES dbo.Streets (StreetName,StreetTypeID,StreetDirectionID,Locality,StateID,Postcode))CREATE TABLE dbo.Addresses (StreetName varchar (35) NOT NULL ,StreetTypeID varchar (10) NOT NULL ,StreetDirectionID varchar (2) NOT NULL ,Locality varchar (46) NOT NULL ,StateID varchar (3) NOT NULL ,Postcode char (4) NOT NULL ,StreetNumber varchar (15) NOT NULL ,AddressTypeID varchar (6) NOT NULL ,AddressName varchar (20) NOT NULL ,CONSTRAINT PK_StreetNumberPrefixes PRIMARY KEY CLUSTERED(StreetName,StreetTypeID,StreetDirectionID,Locality,StateID,Postcode,StreetNumber,AddressTypeID,AddressName),CONSTRAINT FK_Addresses_StreetNumbers FOREIGN KEY(StreetName,StreetTypeID,StreetDirectionID,Locality,StateID,Postcode,StreetNumber) REFERENCES dbo.StreetNumbers (StreetName,StreetTypeID,StreetDirectionID,Locality,StateID,Postcode,StreetNumber))
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Oct 19, 2005
I have an application in which i need to get the foreign key fieldsfrom a table and then get all the foreign keys primary key field fromthe linking table. Could some one tell me how i do this usingINFORMATION_SCHEMA. I have tried and can get the foreign keys but notsure how to get the associated primary keys.
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Jul 20, 2005
I have a question with regads to placement of data files/indexes onmultiple filegroups. Here is the current scenario:I have a database comprised of two filegroups - PRIMARY and INDEX. ThePRIMARY filegroup is comprised of two files, one residing on the Rdrive and another residing on the O drive. The INDEX filegroupconsists of a file on the S drive. The transaction logs reside on theT drive. The box itself has five individual drive slots, not RAID'edor mirrored. The tables are created in the PRIMARY filegroup, theindexes in the INDEX group.My question is this: is there any inherent benefit to create thePRIMARY KEYS in a different filegroup? Currently, they are beingcreated in the PRIMARY group along with the actual data tables.Thank you in adavance for any help.Anthony Robinson
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Jul 20, 2005
What query do I use to list the primary key for each user table, i.e.TABLE | PRIMARY_KEY |Regards,Alan*** Sent via Developersdex http://www.developersdex.com ***Don't just participate in USENET...get rewarded for it!
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