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.
Related
I am fairly green when it comes to working with Access and databases in general.
I am asking for your help in figuring out how to set the correct relationships for three tables:
Table 1 contains:
(no unique ID)
SalesTripID
EmployeeName
StartDate
EndDate
*Each record on this table is related to 1 specific employee's 1 specific sales trip
Table 2 contains:
HotelName
HotelStart
HotelEnd
HotelTotal
*This table may contain multiple records that belong to only 1 record on table 1 (for instance, an employee would stay at 2 hotels during their sales trip)
Table 3 contains:
(no unique ID)
MealVendor
MealDate
MealTotal
*This table, similar to Table 2, may have multiple records in it that are tied to the 1 SalesTripID
How do I set something up to show me each SalesTripID, the multiple Table 2, and the multiple Table 3 records associated with it? Do I need to add a Primary Key anything other than Table 1? Is writing a query involved to display the information? Because I am so green, any and all feedback is welcome.
The following is my recommendation:
Add a SalesTripId field on tables 2,3. This is called a ForeignKey.
If SalesTripId in Table1 is not unique (i.e. each employee can have a trip with the same Id as another employee), add another field (Id) in Table1. You can use Access' AutoNumber type for that field.
I recommend always having a primary key in your tables. But you can skip the Id fields in tables 2,3.
I am creating a relationship between 2 tables:
The relationship I like to form is between the Inventory an InventoryExtended tables.
The primary key for the Inventory table is InvID (Inventory ID).
The reason why I created the InventoryExtended is becauses only 1% of the inventory items in the Inventory table will need additional or extended fields, the rest will not.
Instead of adding these additional fields in the Inventory table where 99% will be blank for 50 additional fields that I need I decided to create an InventoryExtended table and store the 50 fields there.
The relationship between the Inventory an InventoryExtended table will be 1 to 1.
Meaning, for the 1% of the records in the Inventory table , the InvId will be the same as the InvId in the InventoryExtended table.
My question is that should the InvID in the InventoryExtended table be a FK (Foreign Key) or should it be a PK and a FK?
I am thinking it should be a PK and a FK as there the InvID will be unique in the InventoryExtended table.
Thanks in advance.
You are correct.
The InvID should be a PRIMARY KEY and a FOREIGN KEY as it will be unique in the InventoryExtended table.
This type of relationship is indeed 1:1 or (more accurately) 1::0..1, as only some of the rows in the Inventory table will have a related row in InventoryExtended.
Also note that the InventoryExtended (InvID) should not have the IDENTITY property, even if the Inventory (InvID) has it.
The InvID will be both a PK and FK for the extended table.
If you know in advance (meaning when you attempt to fetch data) whether or not a particular inventory type will have the extended data, for such records you can even skip the original table altogether and simply use two disjoint tables smallInventory and bigInventory such that no records of one are present in the other.
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 three tables: Employee, Emp_Address and Emp_AddressDetail.
Employee table is master and Emp_Address is detail.
Emp_Address is master and Emp_AddressDetail is detail.
I want to copy all rows from a table to another table.
How can I do it?
If I understand your question correct you want to insert data from one table to another? If so, you should have a look at the INTO statement. http://msdn.microsoft.com/en-us/library/ms188029.aspx
SELECT * INTO dbo.OneTable FROM Production.AnotherTable
If the tables have foreign keys defined, and those foreign key definitions need to be set on the new database, than you need to take a look at the data diagrams, and identify any tables that do not have foreign key columns. In your case the copy order will be Employee, Emp_Address, Emp_AddressDetail
If you do not have explicit SQL Server maintained foreign keys, or if the foreign keys are not set on the target database, you can just copy the data in any order you like.
Note that it's entirely possible to paint yourself into a corner, e.g. if there was field in the Employee table called PrimaryAddress that would be a foreign key to the Emp_Address table.
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.