I tried using the code below to add two foreign keys to the table products but it wont add foreign keys if i run the two on one run, they work individualy but not if i code it the way below:
ALTER TABLE products
ADD FOREIGN KEY (CategoryI) REFERENCES categories (CategoryID),
ADD FOREIGN KEY (SupplierID) REFERENCES suppliers (SupplierID);
two alter table to make two foreign keys from separate tables
Related
I have made a simple relation table. All consist of three tables:
Tables for storing personal data (Table_Person)
Table for storing address data (Table_Address)
Table to store the relationship between Table_Person and Table_Address (Table_PersonAddress).
What I want to ask is can I delete the primary key in Table_PersonAddress so that Table_PersonAddress doesn't have a primary key and all that's left is the personID and addressID?
Below is an example of a database relation that I made:
enter image description here
Assuming you don't have any foreign key constraints setup on the junction table (that is, the third table which just stores relationships between people and their addresses), you could delete a person from the first table, while leaving behind the relationships in the third table. However, just because you could do this, does not mean you would want to. Most of the time, if you remove a person from the first table, you would also want to remove all of his relationships from the third table. One way to do this in SQLite is by adding cascading delete constraints to the third table, when you create it:
CREATE TABLE Table_PersonAddress (
...
CONSTRAINT fk_person
FOREIGN KEY (personID)
REFERENCES Table_Person (ID)
ON DELETE CASCADE
)
You probably would also want to add a similar constraint for the address field in the third table, since removing an address also invalidates all relationships involving that address.
Note that SQLite does not allow a cascading delete constraint to be added to table which already exists. You will have to recreate your tables somehow in order to add these constrains.
You can delete it, but my advice is to set a composite PRIMARY KEY for the 2 columns personID and addressID so each row is guaranteed to be UNIQUE.
PRIMARY KEY (personID, addressID)
and remember that in SQLite you always have the rowid column to use it as an id of the row if needed.
So create the table with this statement:
DROP TABLE IF EXISTS PersonAddress;
CREATE TABLE PersonAddress (
personID INTEGER,
addressID INTEGER,
PRIMARY KEY(personID, addressID),
FOREIGN KEY (personID) REFERENCES Person (personID) ON DELETE CASCADE,
FOREIGN KEY (addressID) REFERENCES Address (addressID) ON DELETE CASCADE
);
One more thing: why did you define personID and addressID as TEXT?
Surely SQLite is not at all strict at data type definitions, but since the columns they reference are INTEGER they also should be INTEGER.
My issue is that I am getting a foreign key constraint error when I try to add a column to a table. Not a row, a column!
My table is called Screens. It has two tables with foreign key dependencies. They are called Topic and ScreenTypes. Both tables are very small and they only have 2 columns each (id and name). The Screens table contains the columns TopicId and ScreenTypeId plus a couple of other columns. All three table have primary indexes. Everything has been working fine for the past few weeks.
Then, I tried to add a new column to the Screens table called ScreenNumber. The new column is numeric and has no restrictions whatsoever. But, when I tried to commit the change to the schema, I got a foreign key constraint error.
I thought I would get around it by removing the foreign key constraint, adding the column and then adding the foreign key constraint back. But, when I tried to remove the foreign key constraint, I got another foreign key constraint error.
Any help would be greatly appreciated! I have no idea what is causing this and I am past my deadline for this project.
My table is called Screens. It has two tables with foreign key
dependencies. They are called Topic and ScreenTypes. Both tables are
very small and they only have 2 columns each (id and name). The
Screens table contains the columns TopicId and ScreenTypeId plus a
couple of other columns. All three table have primary indexes.
Everything has been working fine for the past few weeks.
From the above and your comments then this appears to create the Screens Table, the Topics Table and the ScreenTypes table and additionally populate the tables with some data:-
DROP TABLE IF EXISTS Screens;
CREATE TABLE IF NOT EXISTS Screens (
id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT UNIQUE,
Video TEXT NOT NULL,
TopicId INTEGER NOT NULL,
Instructions TEXT,
ScreenTypeId INTEGER,
SortOrder INTEGER DEFAULT (10),
Image TEXT,
NewColumn INTEGER,
FOREIGN KEY (TopicId) REFERENCES Topics (id),
FOREIGN KEY (ScreenTypeId) REFERENCES ScreenTypes (id)
)
;
DROP TABLE IF EXISTS Topics;
CREATE TABLE IF NOT EXISTS Topics (ID INTEGER PRIMARY KEY, name TEXT);
DROP TABLE IF EXISTS ScreenTypes;
CREATE TABLE IF NOT EXISTS ScreenTypes (ID INTEGER PRIMARY KEY, name TEXT);
INSERT INTO Topics (name) VALUES ('Topic1'),('Topic2'),('Topic3'),('Topic4');
INSERT INTO ScreenTypes (name) VALUES ('SreenType1'),('ScreenType2'),('ScreenType3'),('ScreenType4');
INSERT INTO Screens (Video,TopicId,Instructions,ScreenTypeId,Image,NewColumn) VALUES
('Video1',2,'do this 001',3,'Image1','blah'),
('Video2',2,'do this 002',3,'Image2','blah'),
('Video3',1,'do this 002',1,'Image3','blah'),
('Video4',3,'do this 004',4,'Image4','blah'),
('Video5',4,'do this 005',1,'Image5','blah')
;
Then, I tried to add a new column to the Screens table called
ScreenNumber. The new column is numeric and has no restrictions
whatsoever. But, when I tried to commit the change to the schema, I
got a foreign key constraint error.
The following works :-
ALTER TABLE Screens ADD COLUMN ScreenNumber INTEGER DEFAULT 100;
as per :-
ALTER TABLE Screens ADD COLUMN ScreenNumber INTEGER DEFAULT 100
OK
Time: 0.083s
and then using the following
SELECT * FROM Screens;
The result is :-
As can be seen, there were no FK constraint conflicts and the column has been added and the default value of 100 applied.
I suspect that your issues with FK Constraints is that you are progressively try to correct issues.
First (at a guess) you try altering (renaming) the Screens table but can't because of the Fk constraint conflicts with the Fields table. You then try altering the Fields table but still you get FK conflicts, due to :-
If an "ALTER TABLE ... RENAME TO" command is used to rename a table that is the parent table of one or more foreign key constraints, the definitions of the foreign key constraints are modified to refer to the parent table by its new name. The text of the child CREATE TABLE statement or statements stored in the sqlite_master table are modified to reflect the new parent table name.
SQLite Foreign Key Support - 5. CREATE, ALTER and DROP TABLE commands
Of course, if acccording to your description, you only want to add the column then the ALTER TABLE Screens ADD COLUMN ScreenNumber INTEGER (with default value if wanted) works without the need to rename tables.
Is there any way in SQLite3 to have a foreign key in the main database that references columns in an attached database (or vice-versa?)
I hope to share the attached (read-only) database between multiple processes, each of which has its own (read/write) main database.
I create the parent table like this (in database 'ParentDB'):
create table Parent (id integer primary key);
Now I try this in the main database:
attach 'parent.sqlite3' as ParentDB;
create table Child (id integer not null references Parent (id),
constraint PK_Child primary key (id));
insert into ParentDB.Parent (id) values (42);
When I try it it creates the foreign key with no errors. Now I try to insert a row into the child table:
insert into Child (id) values (42);
And I get this error:
Error: no such table: main.Parent
So it seems it always assumes the parent and child tables belong to the same database.
Also the foreign key syntax does not allow you to specify which database the parent table belongs to.
Is there a workaround?
This question is related, but here both the parent and child tables are in the same attached database, whereas I have them in separate databases.
SQLite's built-in foreign key constraints do not work across databases.
The only workaround would be to manually write check constraints and triggers that do the same checking.
Using the C API, I don't see a way to determine the foreign key constraints for a named table?
Given this example:
CREATE TABLE artist(
artistid INTEGER PRIMARY KEY,
artistname TEXT
);
CREATE TABLE track(
trackid INTEGER,
trackname TEXT,
trackartist INTEGER,
FOREIGN KEY(trackartist) REFERENCES artist(artistid)
);
sqlite3_table_column_metadata() will tell you it's a primary key, autoincrement, etc. but how
do I get the foreign key constraints?
FOREIGN KEY(trackartist) REFERENCES artist(artistid)
I want to be able to get a list back for table "track" that there are foreign keys back to table Artist column artistid?
I don't see an api to do this? I need to do this programmaticlly upon opening the database, for purposes of aggregation.
Thanks.
After using PRAGMA foreign_key_list(Valuation);
I got back:
PRAGMA foreign_key_list(Valuation);
0|0|Stock|StockId|Id|NO ACTION|NO ACTION|NONE
I understand I need to split on the vertical bar, but what are the first two columns? 0|0 ?
Please note that (foreign) keys can consist of multiple columns, so it would not make sense to return this as column information.
To get information about a table's foreign keys, use this:
PRAGMA foreign_key_list(table-name);
This pragma returns one row for each foreign key constraint created by a REFERENCES clause in the CREATE TABLE statement of table "table-name".
I want to modify the update option of one foreign key.
For this I executed this command:
alter table testusers.ORDERS
DROP CONSTRAINT ORDER_FK_2,
ADD CONSTRAINT ORDER_FK_2 FOREIGN KEY(FK_PRODUCER_ID) REFERENCES testuser.PRODUCER (producer_id)
ON UPDATE CASCADE ON DELETE CASCADE;
If I execute this, there is the following error:
SQL-Fehler: ORA-01735: Ungültige Option ALTER TABLE
01735. 00000 - "invalid ALTER TABLE option"
There is no comma separated list for the alter table according to documentation syntax diagram http://docs.oracle.com/cd/B28359_01/server.111/b28286/clauses002.htm#CJAEDFIB
create table orders(order_id number, fk_producer_id number, CONSTRAINT order_pk PRIMARY KEY (order_id));
create table producer(producer_id number, CONSTRAINT producer_pk PRIMARY KEY (producer_id));
alter table orders
ADD CONSTRAINT ORDER_FK_2 FOREIGN KEY( FK_PRODUCER_ID)
REFERENCES PRODUCER (producer_id) ;
alter table orders
DROP CONSTRAINT ORDER_FK_2;
alter table orders
ADD CONSTRAINT ORDER_FK_2 FOREIGN KEY( FK_PRODUCER_ID)
REFERENCES PRODUCER (producer_id) ;
Ahm, yes, and I could not find any ON UPDATE CASCADE syntax either. But I am sure you can work it out now. Otherwise drop a little comment or post a new question.