How bad is normalizing the database to the 3rd form, which requires that all fields depend on nothing but primary key. Consider the first table you create -- users. They have int primary keys, which duplicate the real primary keys -- user names. When user logs in, the user's entry is uniquely identified by its name, which is not primary key. The fundamental design rule -- avoid redundancy -- is violated. A VERY serious reason should be there for that.
Usually, design is compromised by redundancy for performance. Here, both copies are stored in one remote database, but integer keys may be located/used faster. Additionally, using long string references everywhere instead of short integer keys may save a lot of storage space (additionally increasing speed). How serious these impacts are? Am I missing something?
Usually, login names are not allowed to change. You have problems changing primary keys because all the foreign keys must be updated accordingly. Does it reveal that most user databases use character strings as primary keys?
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.
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,
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,
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?
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?
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?
I have a problem that I'm not sure how to handle. In the application I am working on I will be importing fixed length strings from a CD into the database. Each specific character in the string represents some value.
I can't decide if I should just create a single field of 895 characters or create 895 single character fields. When I need data from the database I won't need all 895 characters of information, I'll only need one or a small subset of values.
Does it really matter which approach I take?
Thanks in advance for any advice/tips you can provide.
I want to find the LONGEST NAME in the column and I am trying to use
: Select MAX(name) from tablename
SQL 2000 gives the max as per alphabetical order and in the above example the MAX is john/b
IS there any direct SQL statement to get the MAX name where MAX refers to the LONGEST in terms of length .
I have been able to do it with 2 sql statements where i first find the longest length and then give a query where i match the length..But is there any simpler way??
I am having data where there are empty string in the business keys which should be used for Slowly changing dimesnion type 2, how do i over come this as due to empty strings i am getting new rows even though the rows havent really changed.
example of data is name and salary are business keys
name salary age address dev 23 klddldldlk sdfg 24 34 kdlddlkd
when the same is given as input the row dev 23 klddldldlk is coming as anew row where it already exists how do i over come this
it's like this, i have a temporary table such as create table temp_table (str varchar(50)) and i have a data table create table data_table (str varchar(20))
now i import my data(in which there is some corrupted lines) into the temporary table, they should be all ansi-character strings and no more than 20 characters, but now some wrong datas in which there are wide-characters are mixed in. as the result of these wide-characters, the corrupted strings each takes over 20 bytes, but i can't filter them out, as when i enter in "len(str)", the sql server returns character counts, instead of byte counts, i thought this should only happen when i was using a unicode date type!(e.g. nvarchar). but now the server also behaves like this on those ansi date types. it seems all string manipulating functions refering string length behaves like this.
so when i am trying to run: insert into data_table select str from temp_table where len(str) <= 20 or insert into data_table select left(str,20) from temp_table
it will always end up with a string truncating error String or binary data would be truncated. The statement has been terminated
So now my problem is how to get the count of byte, but character, of a string containing wide-characters?
i'm using sql server 2005 standard version with sp2
"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!
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?
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.
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.
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.
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:
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.
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.
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
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?
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.
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
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?
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.
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.
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
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?
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
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))
