I want to create a DB , where each table's PK will be GUID and which will be unique across the DB,
Example: my DB name is 'LOCATION'. And I have 3 table as 'CITY' , 'STATE' and 'COUNTRY'.
I want that all the 3 tables have same PK field as GUID ,and that value will be unique across DB.
How to do this in SQL Server, any idea? I have never used SQL Server before, so it will be helpful if briefly explained.
create table CITY (
ID uniqueidentifier not null primary key default newid(),
.
.
.
)
Repeat for the other tables.
What do you mean exactly ?
Just create the table, add an Id field to each table, set the data type of the Id field to 'uniqueidentifier', and you're good to go.
Next, add a primary constraint on those columns, and make sure that, when inserting a new record you assign a new guid to that column (for instance, by using the newid() function).
I can't think of any good reason to have a unique number shared by 3 tables, why not just give each table a unique index with a foreign key reference? Indexed fields are queried quicker than random numbers would be.
I would create a 'Location' table with foreign keys CityId, StateId & CountryId to link them logically.
edit:
If you are adding a unique id across the City, State and Country tables then why not just have them as fields in the same table? I would have thought that your reason for splitting them into 3 tables was to reduce duplication in the database.
Related
I have a problem to set correct constraint to make sure one column has and only has one matched column within the table.
For example, company Apple has Bloomberg ticker AAPL:US and only has this ticker. Otherwise, SQL Server will notice there is a error.
I try to use constraint with unique, but it does not work.
I imagine that your schema might be a standard one using a junction table. That is, your tables might look something like:
company (id, name)
ticker (id, name)
company_ticker (id_company, id_ticker)
That is, the company_ticker table is a junction table which stores the relationships between companies and tickers. Normally, this table would by default be many-to-many. But if you want to restrict a company to having only one ticker, then you may place a unique constraint on the id_company column:
CREATE TABLE company_ticker (
id_company INT NOT NULL,
id_ticker INT NOT NULL,
PRIMARY KEY (id_company, id_ticker),
CONSTRAINT cnstr UNIQUE (id_company)
);
With the above unique constraint in place, your schema will only allow a given company to have one relationship with some ticker.
I have read few posts and articles about NEWID() in MS SQL. Before I decide should I use this method or not I would like to get some information. My Single Page App has few tables. One of the tables should store unique key for each customer. I'm wondering if I should use NEWID() also how I should store that id in the table? I was looking over dataypes and there is unique-identifier type. Few articles mentioned that I will have potential problems with performance especially if I would be joining over 100k to some other tables. I will have this scenario where I would have to join these records to different tables. If anyone can provide some answers or suggestions that would be great. Thanks in advance!
Here is example of my Table:
Column Name Data Type Allow Nulls
hm_id int Unchecked // auto-increment id
hm_studentID uniqueidentifier Unchecked // primary key
hm_firstName varchar(50) Checked
hm_lastName varchar(50) Checked
hm_dob datetime Checked
Old version
I have a Person table and the table Company.
both tables have a column Id (Identity)
Table Company have Ids of 1 to 165
In the table Person have Ids 1 until 2029
New Version
In the new version of the system, was created a table Entity.
This table contains the records of the Companies and People
The Company and Person tables will be maintained, referring to the Entity table.
The Id in table Entity will be the same in Company or Person table
Question
Both tables have multiple relationships with other tables.
Table Entity (as well as others) has a column ID (identity).
The problem is that the Id were repeated when the two tables together (It was to be expected).
How to import without losing relationships?
Attempts
I thought of changing the value of Ids in Company table, starts from 2030.
Thus the Ids would not duplicate when joining the two tables.
But this creates another questions.
How to do this without losing existing relationships?
How to change the Id of a row in the table and this is reflected in all tables which it relates?
I would like to do this using only DDL (SQL Server)
I thought of changing the value of Ids in Company table, starts from 2030. Thus the Ids would not duplicate when joining the two tables.
Create foreign key constraints on the Person table to all related tables (or alter the existing foreign key constraints) with ON UPDATE CASCADE. Then update the Person table and change the values if the id columns - these changes will cascade to the related tables.
To stop further problems, maybe change the identity columns in Person and Company to something like identity( 1000, 3 ) and identity (1001, 3) respectively.
However, I think the best idea is to have a different EntityID column in the Entity table, unrelated to PersonID and CompanyID. The Entity table would also have a column called AltEntityID or BusinessKey that contains the id from the other table and that does not have a unique constraint or a foreign key constraint.
And if you make small modification to your attempt - add new column, say newId, to Company and to Person to manage relation with Entity and leave id columns as is. Why this is the simpliest way? Because new columns shouldnot be identity columns, from one side. From the other side, you can leave all logic of relating other tables with Company and Person intact.
I am developing a system in which I have a table Employees with multiple columns related to employees. I have a column for the JobTitle and another column for Department.
In my current design, the JobTitle & the Department columns are compound foreign keys in the Employees table and they are linked with the Groups table which has 2 columns compound primary key (JobTitle & Department) and an extra column for the job description.
I am not happy about this design because I think that linking 2 tables using 2 compound varchar columns is not good for the performance, and I think it would be better to have an Integer column (autonumber) JobTitleID used as the primary key in the Groups table and as a foreign key in the Employees table instead of the the textual JobTitle & the Department columns.
But I had to do this because when I import the employees list (Excel) into my Employees table it can just be directly mapped (JobTitle --> JobTitle & Department --> Department). Otherwise if I am using an integer index as primary key I would have then to manually rename the textual JobTitle column in the excel sheet to a number based on the generated keys from the Groups table in order to import.
Is it fine to keep my database design like this (textual compound primary key linked with textual compound foreign key)? If not, then if I used an integer column in the Groups table as primary key and the same as a foreign key in the Employees table then how can I import the employees list from excel directly to Employees table?
Is it possible to import the list from Excel to SQL Server in a way that the textual JobTitle from the excel sheet will be automatically translated to the corespondent JobTitleID from the Groups table? This would be the best solution, I can then add JobTitleID column in the Groups table as a primary key and as a foreign key in the Employees table.
Thank you,
It sounds like you are trying to make the database table design fit the import of the excel file which is not such a good idea. Forget the excel file and design your db tables first with correct primary keys and relationships. This means either int, bigint or guids for primary keys. This will keep you out of trouble unless you absolutely know the key is unique such as in a SSN. The when you import, then populate the departments and job titles into their respective tables creating their primary keys. Now that they are populated, add those keys to the excel file that can be imported into the employees table.
This is just an example of how I would solve this problem. It is not wrong to use multiple columns as the key but it will definitely keep you out of harms way if you stick with int, bigint or guids for your primary keys.
Look at the answer in this post: how-to-use-bulk-insert...
I would create a simple Stored Procedure that imports your excel data into a temporary unrestricted STAGING table and then do the INSERT into your real table by doing the corresponding table joins to get the right foreign keys and dump the rows that failed to import into an IMPORT FAIL table. Just some thoughts...
I have a table, Contacts, with a primary key of ContactID, which is an identity column. I have another table, Person, with a primary key of PersonID that is a foreign key to ContactID. When I insert a record into Person, I would like PersonID to pull the corresponding identity from ContactID in Contact.
In Access, I simply make a query that references both tables, and it will fill in the foreign key column with the corresponding value in the identity (autonumber) column.
SELECT Person.PersonID, Person.FirstName, Person.MiddleName, Person.LastName, Contact.ContactID, Contact.EmailAddress, Contact.PhoneNumber
FROM (Contact INNER JOIN Person ON Contact.ContactID = Person.PersonID);
How can we achieve this in SQLServer 2008 R2? I have been programming triggers to update the keys, but it seems like there ought to be a better way.
Thank you very much for your assistance.
When you insert to the first table, you use the OUTPUT clause to pull the identity value and then you can use it to insert to the child table.
You can also use scope_identity() to do the same thing, but OUTPUT is the preferred method. Do not under any circumstances use ##Identity as it often will give incorrect results and mess up your data integrity.
Look up how to use them in Books Online.