So let's say I have these two tables...
IF NOT EXISTS (SELECT * FROM sysobjects WHERE name='UnitsDef' AND xtype='U')
CREATE TABLE UnitsDef
(
UnitsID INTEGER PRIMARY KEY,
UnitsName NVARCHAR(32) NOT NULL,
UnitsDisplay NVARCHAR(8) NOT NULL
);
IF NOT EXISTS (SELECT * FROM sysobjects WHERE name='Dimensions' AND xtype='U')
CREATE TABLE Dimensions
(
DimID INTEGER PRIMARY KEY IDENTITY(0,1),
DimX FLOAT,
DimXUnitsID INTEGER DEFAULT 0,
DimY FLOAT,
DimYUnitsID INTEGER DEFAULT 0,
DimZ FLOAT,
DimZUnitsID INTEGER DEFAULT 0,
FOREIGN KEY (DimXUnitsID) REFERENCES UnitsDef(UnitsID),
FOREIGN KEY (DimYUnitsID) REFERENCES UnitsDef(UnitsID),
FOREIGN KEY (DimZUnitsID) REFERENCES UnitsDef(UnitsID)
);
I'll insert data into the first table similar to this...
INSERT INTO UnitsDef (UnitsID, UnitsName, UnitsDisplay) VALUES (0, 'inch', 'in.');
INSERT INTO UnitsDef (UnitsID, UnitsName, UnitsDisplay) VALUES (1, 'millimeter', 'mm');
INSERT INTO UnitsDef (UnitsID, UnitsName, UnitsDisplay) VALUES (2, 'degree', '°');
Am I going about this the right way? This is a simplified version of the problem, but I need to know which unit each measurement is given in. Is there a better design practice for this type of situation?
How would I handle the ON DELETE and ON UPDATE for these foreign keys? If I try to cascade deletes and updates, SQL Server would not be so happy about that.
Your method is pretty good. I would make the suggestion right off that UnitsId be an identity column, so it gets incremented. Your inserts would then be:
INSERT INTO UnitsDef (UnitsName, UnitsDisplay) VALUES ('inch', 'in.');
INSERT INTO UnitsDef (UnitsName, UnitsDisplay) VALUES ('millimeter', 'mm');
INSERT INTO UnitsDef (UnitsName, UnitsDisplay) VALUES ('degree', '°');
You should also make the string columns unique in UnitsDef and give them case-sensitive collations. After all, Ml and ml are two different things ("M" is mega and "m" is milli).
You might also want to combine the units and values into a single type. This has positives and negatives. For me it adds overhead, but it can help if you want to support a fuller algebra of types.
Related
English is not my native language, so I might have misused words Enumerator and Enumerable in this context. Please get a feel for what I'm trying to say and correct me if I'm wrong.
I'm looking into not having tables for each enumerator I need in my database.
I "don't want" to add tables for (examples:) service duration type, user type, currency type, etc. and add relations for each of them.
Instead of a table for each of them which values will probably not change a lot, and for which I'd have to create relationships with other tables, I'm looking into having just 2 tables called Enumerator (eg: user type, currency...) and Enumerable (eg: for user type -> manager, ceo, delivery guy... and for currency -> euro, dollar, pound...).
Though here's the kicker. If I implement it like that, I'm loosing the rigidity of the foreign key relationships -> I can't accidentally insert a row in users table that will have a user type of some currency or service duration type, or something else.
Is there another way to resolve the issue of having so many enumerators and enumerables with the benefit of having that rigidity of the foreign key and with the benefit of having all of them in just those 2 tables?
Best I can think of is to create a trigger for BEFORE UPDATE and BEFORE INSERT to check if (for example) the column type of user table is using the id of the enumerable table that belongs to the correct enumerator.
This is a short example in SQL
CREATE TABLE [dbo].[Enumerator]
(
[Id] INT NOT NULL PRIMARY KEY,
[Name] VARCHAR(50)
)
CREATE TABLE [dbo].[Enumerable]
(
[Id] INT NOT NULL PRIMARY KEY,
[EnumeratorId] INT NOT NULL FOREIGN KEY REFERENCES Enumerator(Id),
[Name] VARCHAR(50)
)
INSERT INTO Enumerator (Id, Name)
VALUES (1, 'UserType'),
(2, 'ServiceType');
INSERT INTO Enumerable (Id, EnumeratorId, Name) -- UserType
VALUES (1, 1, 'CEO'),
(2, 1, 'Manager'),
(3, 1, 'DeliveryGuy');
INSERT INTO Enumerable (Id, EnumeratorId, Name) -- ServiceDurationType
VALUES (4, 2, 'Daily'),
(5, 2, 'Weekly'),
(6, 2, 'Monthly');
CREATE TABLE [dbo].[User]
(
[Id] INT NOT NULL PRIMARY KEY IDENTITY (1,1),
[Type] INT NOT NULL FOREIGN KEY REFERENCES Enumerable(Id)
)
CREATE TABLE [dbo].[Service]
(
[Id] INT NOT NULL PRIMARY KEY IDENTITY (1,1),
[Type] INT NOT NULL FOREIGN KEY REFERENCES Enumerable(Id)
)
The questions are:
Is it viable to resolve enumerators and enumerables with 2 tables and with before update and before insert triggers, or is it more trouble than it's worth?
Is there a better way to resolve this other than using before update and before insert triggers?
Is there a better way to resolve enumerators and enumerables that is not using 2 tables and triggers, nor creating a table with relations for each of them?
I ask for your wisdom as I don't have one or more big projects behind me and I didn't get a chance to create a DB like this until now.
These are the tables I already have:
CREATE TABLE Gyartok
(
GyID INT IDENTITY(2, 3),
Nev VARCHAR(20),
CONSTRAINT PK_Gyartok PRIMARY KEY (GyID)
)
CREATE TABLE Focicsuka
(
CsID INT IDENTITY(2, 2),
Meret INT,
CONSTRAINT PK_Focicsuka PRIMARY KEY (CsID)
)
CREATE TABLE FcsGyartjaGya
(
GyID INT IDENTITY(3, 2),
CsID INT,
Ar INT,
CONSTRAINT FK_FcsGyartjaGya1
FOREIGN KEY (GyID) REFERENCES Gyartok(GyID),
CONSTRAINT FK_FcsGyartjaGya2
FOREIGN KEY (CsID) REFERENCES Focicsuka(CsID),
CONSTRAINT PK_FcsGyartjaGya
PRIMARY KEY (GyID, CsID)
)
The problem is that every time I try to add new values to the table (like such)
INSERT INTO FcsGyartjaGya (Ar) VALUES (300);
I get an error saying I didn't initialize the CsID INT column:
Cannot insert the value NULL into column 'CsID', table 'Lab3.dbo.FcsGyartjaGya'; column does not allow nulls. INSERT fails.
I know I must initialize it with something, but I have no idea what do to it with, because IDENTITY(x, y) doesn't work (it's occupied by another column already) and adding another parameter to the code (like such)
INSERT INTO FcsGyartjaGya (Ar, CsID) VALUES (300, 7);
creates another error which says
The INSERT statement conflicted with the FOREIGN KEY constraint "FK_FcsGyartjaGya1". The conflict occurred in database "Lab3a", table "dbo.Gyartok", column 'GyID'.
It is important to note that I already filled every column with data, so that couldn't be the problem.
As I mention in the comments, your INSERT will work fine, provided the stars align correctly. For your table Gyartok you have GyID as your PRIMARY KEY, which is defined as a IDENTITY(2,3); so the first value generated is 2 and then each row attempted to be INSERTed will increment by 3.
So, if we run the following, we get the IDs 2, 5, 7 and 17. (11 and 14 are skipped as the INSERT failed).
CREATE TABLE Gyartok (
GyID INT IDENTITY(2, 3),
Nev VARCHAR(20),
CONSTRAINT PK_Gyartok PRIMARY KEY (GyID)
);
GO
INSERT INTO dbo.Gyartok (Nev)
VALUES ('asdfjahsbvd'),
('ashjkgdfakd'),
('kldfbhjo');
GO
INSERT INTO dbo.Gyartok (Nev)
VALUES (REPLICATE('A',25)), --Force a truncation error
('ashjkgdfakd');
GO
INSERT INTO dbo.Gyartok (Nev)
VALUES (REPLICATE('A',15));
Let's now add some data for your other table:
CREATE TABLE Focicsuka (
CsID INT IDENTITY(2, 2),
Meret INT,
CONSTRAINT PK_Focicsuka PRIMARY KEY (CsID)
)
INSERT INTO dbo.Focicsuka (Meret)
VALUES(12),
(25);
Now we want to INSERT into the table FcsGyartjaGya, defined as the following:
CREATE TABLE FcsGyartjaGya (
GyID INT IDENTITY(3, 2),
CsID INT,
Ar INT,
CONSTRAINT FK_FcsGyartjaGya1 FOREIGN KEY (GyID) REFERENCES Gyartok(GyID),
CONSTRAINT FK_FcsGyartjaGya2 FOREIGN KEY (CsID) REFERENCES Focicsuka(CsID),
CONSTRAINT PK_FcsGyartjaGya PRIMARY KEY (GyID, CsID)
)
This has a IDENTITY on GyID, but defined as an IDENTITY(3,2), so the first value is 3 and then incremented by 2.
As this has 2 foreign keys, on GyID and CsID when we INSERT the row the values must appear in the respective tables. As GyID is defined as anIDENTITY(3,2) however, this is where we need to rely on the Stars luck for the INSERT to work. Why? Well 2 + (3*n) and 3+(2*n) can give very different numbers. The first are as you saw at the start of this answer. For the latter, we have numbers like 3, 5, 7, 9, 11. As you can see, only 1 in 3 of these numbers match a number in our original sequence, so luck is what we are going to be relying on.
Let's, therefore, try a single INSERT.
INSERT INTO dbo.FcsGyartjaGya (CsID,Ar)
VALUES(2,1);
The INSERT statement conflicted with the FOREIGN KEY constraint "FK_FcsGyartjaGya1". The conflict occurred in database "Sandbox", table "dbo.Gyartok", column 'GyID'.
Well, that didn't work, but it was expected. 3 isn't a value in the table Gyartok. Let's try again!
INSERT INTO dbo.FcsGyartjaGya (CsID,Ar)
VALUES(2,2);
It worked! The stars Luck was our side, and the IDENTITY value was a value in the table Gyartok. Let's try a couple of rows this time!
INSERT INTO dbo.FcsGyartjaGya (CsID,Ar)
VALUES(4,3),
(4,4);
The INSERT statement conflicted with the FOREIGN KEY constraint "FK_FcsGyartjaGya1". The conflict occurred in database "Sandbox", table "dbo.Gyartok", column 'GyID'.
No!! Not again. :( That's because the stars didn't align; 7 and 9 aren't in the other table. But wait, 11 was in the sequence, so let's try that:
INSERT INTO dbo.FcsGyartjaGya (CsID,Ar)
VALUES(4,5);
Error, again?! No, it cannot be!!! :( Oh wait, I forgot, the stars were against us before, because that INSERT failed against Gyartok for the value of 11. I need to wait for 17!
--13 fails
INSERT INTO dbo.FcsGyartjaGya (CsID,Ar)
VALUES(4,6);
GO
--15 fails
INSERT INTO dbo.FcsGyartjaGya (CsID,Ar)
VALUES(4,6);
GO
--17 works!
INSERT INTO dbo.FcsGyartjaGya (CsID,Ar)
VALUES(4,6);
And now we have another row in our table.
So what is the problem? Your design. GyID is defined as an IDENTITY and a FOREIGN KEY; meaning you are at the "whims" of SQL Server generating a value valid. This is not what you want. Just don't define the column as an IDENTITY and then INSERT the data with all 3 of your columns defined:
CREATE TABLE FcsGyartjaGya (
GyID int,-- IDENTITY(3, 2),
CsID INT,
Ar INT,
CONSTRAINT FK_FcsGyartjaGya1 FOREIGN KEY (GyID) REFERENCES Gyartok(GyID),
CONSTRAINT FK_FcsGyartjaGya2 FOREIGN KEY (CsID) REFERENCES Focicsuka(CsID),
CONSTRAINT PK_FcsGyartjaGya PRIMARY KEY (GyID, CsID)
)
GO
INSERT INTO dbo.FcsGyartjaGya (GyID, CsID, Ar)
VALUES(2,2,1),
(2,4,2),
(5,4,3),
(8,2,4),
(8,4,5);
And all these rows insert fine.
I think there is a bit confusion, if I understand correctly what You're trying to do, then you have two tables each with their own id, which is based on an identity column, so you get new values in those for free.
Then you are trying to make a relation table with extra data.
Issue 1: You cannot have FcsGyartjaGya.GyID be identity if it refers to Gyartok.GyID because you will want to insert into it and not rely on an auto increment. If it doesn't refer to the same it should have another name or my head will possibly explode :))
Issue 2: When populating a relation table you need to insert it with what pairs you want, there is no way SQL server can know how it should match these identity pairs in the relation table
I think this is what people are aiming at in the comments, for example
to insert a relationship between row with Focicsuka.CsID = 1 to Gyartok.GyID 7 and adding Ar = 300 have to look like
INSERT INTO FCSGYARTJAGYA(GYID, CSID, AR)
VALUES(7, 1, 300)
Unless You've forgotten to mention that you want to put some value for each of some value or based on something which can be scripted, in other words unless You have logics to define the pairs and their values, relationship tables cannot have defaults on their foreign key fields.
So I have a problem, I was wondering is there a way of inserting the (ID VALUES) to each column since I forgot. I have a really long code. Is there a way for me to select a piece of code to paste the number ID values or a Method of some sort? Or is my only option to do it manually?
CREATE TABLE tASTON
(AsM_ID int Primary Key Not Null IDENTITY(1,1),Make Nvarchar(50), Model nvarchar (50))
Insert into tASTON(AsM_ID,Make,Model) Values ('Aston Martin','DB4')
Insert into tASTON (AsM_ID,Make,Model) Values ('Aston Martin','DB5')
Insert into tASTON (AsM_ID,Make,Model) Values ('Aston Martin','DB6')
Insert into tASTON (AsM_ID,Make,Model) Values ('Aston Martin','DB7')
Insert into tASTON (AsM_ID,Make,Model) Values ('Aston Martin','Vanquish') etc...
Seeing it's an IDENTITY column, there's no need to manually INSERT values. This ought to work:
Insert into tASTON(Make,Model) Values ('Aston Martin','DB4')
Update: Removed brand, as it was confusing and a mistake on my part. Replaced Brand with Make, instead.*
Unrelated, but judging by the name of the table, are you really creating one table per brand of car? If so, I'd suggest creating a make and a car table, where you then implement a key relationship between tCar and tMake:
CREATE TABLE tCAR
(
CAR_ID int Primary Key Not Null IDENTITY(1,1)
, MAKE_ID int FOREIGN KEY REFERENCES tMake(MAKE_ID)
, Model nvarchar (50)
)
Typically when I represent a parent child hierarchy I have a table as follows (I might also add additional depth columns to speed things up), where parents and children are both foreign key relationships to rows from the same entity table.
Entity Relationships
composite pkey
child id
parent id
What I am trying to figure out is how to limit the depth of the tree to one. In other words, if somebody is the parent of a child, how to I prevent that parent from being a child in itself, so it is impossible to have grandparents or even further?
Depending on your RDBMS, you can handle something like this in an INSERT/UPDATE trigger. For simply restricting a parent to not also be a child it shouldn't be too bad (although I hate using triggers any more than necessary). If you were trying to limit to a certain number of levels (say 100) then you might start to run into performance issues.
In MS SQL Server you can also use user-defined functions in constraints. There are limits however, so I don't know if it would work here. I'll try to test it though.
EDIT:
I just tested this on MS SQL Server 2008 and it looks like it works correctly:
CREATE FUNCTION dbo.Is_Child (#parent_id INT) RETURNS BIT
AS
BEGIN
DECLARE #return BIT
IF EXISTS (SELECT * FROM dbo.Test_Trees WHERE child_id = #parent_id)
SET #return = 1
ELSE
SET #return = 0
RETURN #return
END
GO
CREATE TABLE dbo.Test_Tree_Objects (
my_id INT NOT NULL,
CONSTRAINT PK_Test_Tree_Objects PRIMARY KEY CLUSTERED (my_id)
)
CREATE TABLE dbo.Test_Trees (
my_id INT NOT NULL IDENTITY,
parent_id INT NOT NULL CHECK (dbo.Is_Child(parent_id) = 0),
child_id INT NOT NULL,
CONSTRAINT PK_Test_Trees PRIMARY KEY CLUSTERED (my_id),
CONSTRAINT FK_Test_Trees_parent_id FOREIGN KEY (parent_id) REFERENCES dbo.Test_Tree_Objects (my_id),
CONSTRAINT FK_Test_Trees_child_id FOREIGN KEY (child_id) REFERENCES dbo.Test_Tree_Objects (my_id)
)
GO
INSERT INTO dbo.Test_Tree_Objects (my_id) VALUES (1), (2), (3), (4), (5)
GO
INSERT INTO dbo.Test_Trees (parent_id, child_id) VALUES (1, 2)
INSERT INTO dbo.Test_Trees (parent_id, child_id) VALUES (2, 3)
DROP TABLE dbo.Test_Trees
DROP TABLE dbo.Test_Tree_Objects
DROP FUNCTION dbo.Is_Child
GO
I have only done databases without relations, but now I need to do something more serious and correct.
Here is my database design:
Kunde = Customer
Vare = Product
Ordre = Order (Read: I want to make an order)
VareGruppe = ehm..type? (Read: Car, chair, closet etc.)
VareOrdre = Product_Orders
Here is my SQL (SQLite) schema:
CREATE TABLE Post (
Postnr INTEGER NOT NULL PRIMARY KEY,
Bynavn VARCHAR(50) NOT NULL
);
CREATE TABLE Kunde (
CPR INTEGER NOT NULL PRIMARY KEY,
Navn VARCHAR(50) NOT NULL,
Tlf INTEGER NOT NULL,
Adresse VARCHAR(50) NOT NULL,
Postnr INTEGER NOT NULL
CONSTRAINT fk_postnr_post REFERENCES Post(Postnr)
);
CREATE TABLE Varegruppe (
VGnr INTEGER PRIMARY KEY,
Typenavn VARCHAR(50) NOT NULL
);
CREATE TABLE Vare (
Vnr INTEGER PRIMARY KEY,
Navn VARCHAR(50) NOT NULL,
Pris DEC NOT NULL,
Beholdning INTEGER NOT NULL,
VGnr INTEGER NOT NULL
CONSTRAINT fk_varegruppevgnr_vgnr REFERENCES Varegruppe(VGnr)
);
CREATE TABLE Ordre (
Onr INTEGER PRIMARY KEY,
CPR INTEGER NOT NULL
CONSTRAINT fk_kundecpr_cpr REFERENCES Kunde(CPR),
Dato DATETIME NOT NULL,
SamletPris DEC NOT NULL
);
CREATE TABLE VareOrdre (
VareOrdreID INTEGER PRIMARY KEY,
Onr INTEGER NOT NULL
CONSTRAINT fk_ordrenr_onr REFERENCES Ordre(Onr),
Vnr INTEGER NOT NULL
CONSTRAINT fk_varevnr_vnr REFERENCES Vare(Vnr),
Antal INTEGER NOT NULL
);
It should work correctly.
But I am confused about Product_Orders.
How do I create an order? For example, 2 products using SQL INSERT INTO?
I can get nothing to work.
So far:
Only when I manually insert products and data into Product_Orders and then add that data to Orders = which makes it complete. Or the other way around (create an order in with 1 SQL, then manually inserting products into Product_orders - 1 SQL for each entry)
You should first create an order and then insert products in the table Product_Orders. This is necessary because you need an actual order with an id to associate it with the table Product_Orders.
You always should create a record in the foreign-key table before being able to create one in your current table. That way you should create a "Post", customer, type, product, order and product_order.
Try this ...
first you have to insert a customer
insert into kunde values(1, 'navn', 1, 'adresse', 1)
then you insert a type
insert into VareGruppe values(1, 'Type1')
then you insert a product
insert into vare values(1, 'product1', '10.0', 1, 1)
then you add an order
insert into ordre values(1, 1, '20090101', '10.0')
then you insert a register to the product_orders table
insert into VareOrdre values (1, 1, 1, 1)
I think this is it. :-)
As the primary keys are autoincrement, don't add them to the insert and specify the columns like this
insert into vare(Nav, Pris, Beholdning, VGnr) values('product1', '10.0', 1, 1)
Use Select ##identity to see the onr value
I think you already have the hang of what needs to happen. But what I think you are getting at is how to ensure data integrity.
This is where Transactions become important.
http://www.sqlteam.com/article/introduction-to-transactions
Is it the SalesPrice (I'm guessing that's what SamletPris means) that's causing the issue? I can see that being a problem here. One common design solution is to have 2 tables: Order and OrderLine. The Order is a header table - it will have the foreign key relationship to the Customer table, and any other 'top level' data. The OrderLine table has FK relationships to the Order table and to the Product table, along with quantity, unit price, etc. that are unique to an order's line item. Now, to get the sales price for an order, you sum the (unit price * quantity) of the OrderLine table for that order. Storing the SalesPrice for a whole order is likely to cause big issues down the line.
A note just in case this is MySQL: If you're using MyISAM, the MySQL server ignores the foreign keys completely. You have to set the engine to InnoDB if you want any kind of integrity actually enforced on the database end instead of just in your logic. This isn't your question but it is something to be aware of.
fbinder got the question right :)