is there anyone who can help me to create a foreign key for my Status table. I need to PLACE a foreign key constraint on the code in the status table, referring to the id in the Building table.
TABLE building
(
build_name VARCHAR2(50,0) NOT NULL,
id NUMBER (38,0) NOT NULL,
mapid NUMBER (10,0) NOT NULL
);
TABLE STATUS
(
code VARCHAR(2 BYTE) NOT NULL,
status_name VARCHAR2(40 BYTE) NOT NULL,
);
Bulding table has constraint building_gmidx with id as primary key.
Here is a quick syntax for your current requirement, however I recommend you to go through the oracle documentation for a proper understanding of what this means.
ALTER TABLE STATUS ADD (
CONSTRAINT status_fk_building FOREIGN KEY (code)
REFERENCES building (id)
ENABLE VALIDATE);
Did you leave out CREATE TABLE *name* to save time when writing the question? The first thing I see is that your Foreign key has to have the same data type and size as your Primary key. If the Tables already exist the code would be:
ALTER TABLE status MODIFY (code NUMBER(38));
From there you would need to
ALTER TABLE status ADD FOREIGN KEY (code) REFERENCES (building_gmidx)
Why is the constraint for building Primary key named building_gmidx and the column plain id?? All Normalized table attributes should be Unique. Wouldn't it be better if you just named the column "id" building_gmidx instead. Just in case there are other types of id's added later you do not have to think about which table "id" pertains to. Let me know if this works.
Related
I'm a beginner and creating my own simple blockchain app for fun. The blockchain itself is fully functional. Now I'm trying to implement a database to store the data of the blockchain (right now I'm writing it to a .txt file). So I want to create the following database schema in sqlite:
CREATE TABLE `Blockchain`
(
`previous_hash` string NOT NULL ,
`timestamp` float NOT NULL ,
`signature_of_transactions` string NOT NULL ,
`index` bigint NOT NULL ,
PRIMARY KEY (`previous_hash`)
);
CREATE TABLE `Wallet`
(
`public_key` string NOT NULL ,
PRIMARY KEY (`public_key`)
);
CREATE TABLE `Transactions`
(
`signature` string NOT NULL ,
`sender` string NOT NULL ,
`recipient` string NOT NULL ,
`amount` float NOT NULL ,
PRIMARY KEY (`signature`)
);
CREATE TABLE `Peer_nodes`
(
`id` string NOT NULL ,
`public_key` string NOT NULL ,
PRIMARY KEY (`id`)
);
ALTER TABLE `Wallet`
ADD CONSTRAINT `fk_Wallet_public_key`
FOREIGN KEY(`public_key`) REFERENCES `Peer_nodes` (`public_key`);
ALTER TABLE `Transactions`
ADD CONSTRAINT `fk_Transactions_signature`
FOREIGN KEY(`signature`) REFERENCES `Blockchain` (`signature_of_transactions`);
ALTER TABLE `Transactions`
ADD CONSTRAINT `fk_Transactions_sender`
FOREIGN KEY(`sender`) REFERENCES `Wallet` (`public_key`);
ALTER TABLE `Transactions`
ADD CONSTRAINT `fk_Transactions_recipient`
FOREIGN KEY(`recipient`) REFERENCES `Wallet` (`public_key`);
Creating the tables with the columns etc. works fine with the script above. The ALTER TABLE queries do not work somehow. This is the following error message I receive:
ALTER TABLE Wallet ADD CONSTRAINT fk_Wallet_public_key FOREIGN KEY(public_key) REFERENCES Peer_nodes (public_key)
ERROR:
As you can see, it has no real error message. I haven't found a possible error in the queries themselves after searching a lot on the internet. What am I doing wrong? I try to do this via phpLitedmin, so maybe the problem is there?
SQLite's ALTER TABLE does not support adding constraints.
You have to include the constraints into the CREATE TABLE statements.
And as already noted by Gordon, foreign key constraints require the target to be a primary or candidate key.
Your foreign key reference is to the wrong column. It should be to the primary key, although it can be to a unique key.
As explained in the documentation:
Usually, the parent key of a foreign key constraint is the primary key
of the parent table. If they are not the primary key, then the parent
key columns must be collectively subject to a UNIQUE constraint or
have a UNIQUE index. If the parent key columns have a UNIQUE index,
then that index must use the collation sequences that are specified in
the CREATE TABLE statement for the parent table.
You should fix the table definition and add the foreign key to use the primary key.
What is the difference between using or not using the CONSTRAINT keyword when working with Foreign Keys on SQL Server?
I noticed that apparently both worked the same in this specific case, without CONSTRAINT:
CREATE TABLE ClientsPhones
(
ClientPhone varchar(10) NOT NULL,
ClientID smallint NOT NULL,
PRIMARY KEY (ClientPhone),
FOREIGN KEY (ClientID) REFERENCES Clients(ClientID)
);
And with CONSTRAINT:
CREATE TABLE ClientsPhones
(
ClientPhone varchar(10) NOT NULL,
ClientID smallint NOT NULL,
PRIMARY KEY (ClientPhone),
CONSTRAINT fk_ClientID
FOREIGN KEY (ClientID) REFERENCES Clients(ClientID)
);
Both didn't let me add records to the table unless the ClientID already existed on the Clients table, and the same ClientID and ClientPhone weren't already on the ClientsPhones table.
Is there any real difference between the two besides the fact that I'm able to name the constraint?
If you don't create constraint.it will automatically create own constraint name
the foreign key index name is generated using the name of the referencing foreign key column Automatically.
So there is no way to see difference of using and not using Constraint keyword. by default constraint name will be defined.
I did some research and don't believe Hell Boy's answer was as clear as it could be and had some misinformation.
Every constraint you add to a database has a name set by default. This includes PRIMARY KEY, FOREIGN KEY, DEFAULT, NOT NULL. It isn't necessarily the name of the column(s) used.
You can imagine that when you don't use the CONSTRAINT keyword SQL Server puts it there as well as generates a name for you.
If you want to remove or change a constrain you would either have to delete the entire table and recreate it with the correct constraints or you can reference the constraint by name and then alter it somewhat like a column using the ALTER keyword. This can be useful for when you need to delete a table with a foreign key. If you name the foreign key constraint you can delete it and then the table instead of having to delete the table the foreign key points to.
I'm convinced I must be doing something incredibly stupid, as it can't be this hard to add a new foreign key to an existing table. However, I'm still stuck. Here's what I'm doing.
First, I created a new column in TPM_USER to store which team a user is on:
ALTER TABLE TPM_USER ADD (
"TEAMID" NUMBER NULL
)
This works without errors, and I can query the TPM_USER table to see the new column has been added. Next, I want TEAMID to refer to a row in the already existing TPM_DEVELOPMENTTEAMS table. So I do:
ALTER TABLE TPM_USER
ADD CONSTRAINT TPM_USER_FK1
FOREIGN KEY(TEAMID)
REFERENCES TPM_DEVELOPMENTTEAMS(TEAMID)
This gives me the error:
ORA-02270: no matching unique or primary key for this column-list
I've checked both TEAMID columns are the same data type (NUMBER) and TEAMID is of course the primary key of the DEVELOPMENTTEAMS table. In fact, here's the schema for DEVELOPMENTTEAMS:
CREATE TABLE TPMDBO.TPM_DEVELOPMENTTEAMS (
TEAMID NUMBER NULL,
NAME VARCHAR2(100) NOT NULL,
ISACTIVE CHAR(1) NULL,
SORTORDER NUMBER NULL,
SHORTNAME VARCHAR2(100) NULL,
GROUPID NUMBER NOT NULL,
CONSTRAINT TPM_DEVELOPMENTTEAMS_PK PRIMARY KEY(TEAMID)
NOT DEFERRABLE
DISABLE NOVALIDATE
)
I even tried the GUI interface in Aqua Data Studio to add the new constraint as well, so I'm sure I didn't misspell anything. What am I doing wrong?
Your PK is disabled. Enable it with:
ALTER TABLE TPM_DEVELOPMENTTEAMS ENABLE CONSTRAINT TPM_DEVELOPMENTTEAMS_PK;
BTW, by declaring it PK, you also made TPM_DEVELOPMENTTEAMS.TEAMID non-NULL (so there is no purpose for NULL after it).
You can only refer the column(or combination of columns) which are either enabled Primary Key or Unique Key for the same/other table.
If you find your constraint disabled in below query then you cant create Foreign Key for that PK/UK. You should enable it.
select constraint_name from dba_constraints
where constraint_type in ('P','U')
and status = 'DISABLED'
and lower(table_name) = lower(:p_table_name);
I am aware of Oracle's create table syntax
CREATE TABLE MyTable(
id int primary key,
...
);
This will create a table called MyTable with an int primary key. So, nothing new here.
but I am having difficulties understanding the following query:
CREATE TABLE departament (
cod_dept INTEGER CONSTRAINT dept_key PRIMARY KEY,
dept_name CHAR(15) NOT NULL,
admission DATE NOT NULL,
localization CHAR(20))
When I look up on Oracle's SQL Developer software on departement's table, I can see 4 columns: cod_dept, dept_name, admission and localization. On the constraints tab, I can also see dept_key, but I am confused as to what this might mean. What is dept_key purpose here?
Edit
Ok, seems it is a way to define the name of the constraint you're adding to the table. My next question is why don't you just call it the same name as the primary key column? From what I've seen it seems Oracle by default just creates a random name for the constraint!
Thanks
When you write id int primary key, Oracle will create a primary key constraint to ensure uniqueness of primary key values. All constraints have names, so in this case Oracle assigns an autogenerated name to this constraint. But you can set a name of this constraint explicitly using the CONSTRAINT syntax:
cod_dept INTEGER CONSTRAINT dept_key PRIMARY KEY
This name may be used later to refer to the constraint, for example, to delete or modify it:
ALTER TABLE department DROP CONSTRAINT dept_key;
EDIT:
Constraint names are unique across the schema, so Oracle can't just use the name of primary key column as a constraint name.
Primary keys can be explicitly be named. dept_key is just a name.
dept_key is the name of the primary key constraint. That means cod_dept is the unique identifier for your table, the mechanism for identifying a row, and so it can only have one occurrence of any given value.
That is the constraint you created representing the primary key.
A table is made up of:
Columns (where the data lives)
Indexes (indexed copies of the data used for faster searching)
Constraints (rules about what data can be in the table, including PK, FK, and check constraints).
dept_key is the name of the constraint. You specified the name here : "INTEGER CONSTRAINT dept_key PRIMARY KEY," so it will create a constraint with the name dept_key.
Another syntax for the same would be to write the following after your CREATE TABLE instruction.
ALTER TABLE department
ADD CONSTRAINT dept_key PRIMARY KEY (cod_dept)
dept_key is then the name of the constraint you created to be the primary key for this table. In order for a database engine to know the primary key, and to index it for fastest results and so forth, it needs to create a known constraint that is indexed. Here, it is you who has given the name which is dept_key.
For you kind information, it is often seen to write PK_[table name] for primary keys constraints and FK_[current_table_name]_[foreign_table_name] for foreign keys constraints.
Hope this helps! =)
I think whenever we create a Primary Key value then by default Oracle will crate constraint for it with the same name but it looks like that u are creating constraint with some other name.
Thank You
create table d(id numeric(1), code varchar(2))
After I create the above table how can I add a composite primary key on both fields and also a foreign key?
In Oracle, you could do this:
create table D (
ID numeric(1),
CODE varchar(2),
constraint PK_D primary key (ID, CODE)
);
alter table d add constraint pkc_Name primary key (id, code)
should do it. There's lots of options to a basic primary key/index depending on what DB your working with.
The ALTER TABLE statement presented by Chris should work, but first you need to declare the columns NOT NULL. All parts of a primary key need to be NOT NULL.
You don't need to create the table first and then add the keys in subsequent steps. You can add both primary key and foreign key while creating the table:
This example assumes the existence of a table (Codes) that we would want to reference with our foreign key.
CREATE TABLE d (
id [numeric](1),
code [varchar](2),
PRIMARY KEY (id, code),
CONSTRAINT fk_d_codes FOREIGN KEY (code) REFERENCES Codes (code)
)
If you don't have a table that we can reference, add one like this so that the example will work:
CREATE TABLE Codes (
Code [varchar](2) PRIMARY KEY
)
NOTE: you must have a table to reference before creating the foreign key.
If using Sql Server Management Studio Designer just select both rows (Shift+Click) and Set Primary Key.