This is a sample of my code. I'm using sql server 2008 R2
create table Entidade(
NIF numeric(9,0) primary key,
nome varchar(250) not null,
tipoEnt varchar(4) check (tipoEnt in ('CE','EC','CEEC',null))
)
create table Curso(
cod int primary key identity(1,1),
descricao text,
nHoras decimal(5,2),
NIFEnt numeric(9,0) references Entidade(NIF),
)
create table AccaoFormacao(
ref int identity(1,1) not null,
codCr int references Curso(cod) not null,
dtInicio date,
dtFim date,
BIFDR numeric(8,0) references Formador(BI),
constraint pkAccaoFormacao primary key(ref, codCr),
)
create table AF_FDO(
codCr int,
refAf int,
BI numeric(8,0) foreign key references Formando(BI),
constraint fkAF_FDO foreign key(codCr, refAf) references AccaoFormacao(codCr, ref),
constraint pkAF_FDO primary key(codCr, refAf, BI)
)
Everything goes fine until I try to create the table AF_FDO, it says:
"Msg 1776, Level 16, State 0, Line 1
There are no primary or candidate keys in the referenced table 'AccaoFormacao' that match the referencing column list in the foreign key 'fkAF_FDO'."
I understand the message but can't figure how to fix it since I'm declaring the primary key in the constraint pkAccaoFormacao it makes no sense to me.
The unique constraint in AccaoFormacao(codCr, ref) works but at the same time it doesn't "fit" in what I'm doing here. AccaoFormacao is a weak entity of Curso thus I have a composite primary key in AccaoFormacao.
EDIT1:
Ok I figured it out after hours I feels stupid.
I changed the constraint fkAF_FDO foreign key(codCr, refAf) references AccaoFormacao(codCr, ref) in AF_FDO to constraint fkAF_FDO foreign key(codCr, refAf) references AccaoFormacao and it worked. It will get the composite primary key of AccaoFormacao as it should, the other way should also work...
Thanks for the help anyway.
There is no PK in AccaoFormacao , take a look at Ref and CodCr , FKS needs to point a PK.
Related
I can not add a referential constraint, both tables has the two columns id and version as primary key. I will only check the integrity that the row is existing without checking version.
CREATE TABLE TABLEE
(ID INTEGER NOT NULL,
VERSION INTEGER NOT NULL,
PRIMARY KEY (ID , VERSION);
CREATE TABLE CHAIR
(ID INTEGER NOT NULL,
VERSION INTEGER NOT NULL,
ID_TABLEE INTEGER,
PRIMARY KEY (ID , VERSION);
ALTER Chair
ADD constraint MYC FOREIGN KEY (ID)
REFERENCES TABLEE (ID)
ON DELETE RESTRICT
Got this error
[Code: -573, SQL State: 42890] A column list specified in the references clause of constraint "MYC " does not identify a unique constraint of the parent table or nickname "TABLEE".. SQLCODE=-573, SQLSTATE=42890, DRIVER=4.28.11
The problem here is that Tablee its primary key consists of two columns id and version. But the integrity check should only be made on the referenced id, not version.
To establish a foreign key on a table the referenced column needs to:
Be a primary key on the other table.
...or at least act as one.
Since you already have a primary key on the referenced table, you can use the second approach and add a UNIQUE and NOT NULL constraints on ID.
For example:
CREATE TABLE TABLEE (
ID INTEGER NOT NULL,
VERSION INTEGER NOT NULL,
PRIMARY KEY (ID , VERSION),
constraint uq1 unique (id) -- added UNIQUE constraint on ID
);
CREATE TABLE CHAIR (
ID INTEGER NOT NULL,
VERSION INTEGER NOT NULL,
ID_TABLEE INTEGER,
PRIMARY KEY (ID , VERSION)
);
ALTER table Chair
ADD constraint MYC FOREIGN KEY (ID)
REFERENCES TABLEE (ID)
ON DELETE RESTRICT;
See running example at db<>fiddle.
Note: If you want ID to have repeated values over the table, then ID is not a key, and cannot be referenced as one.
I have looked into questions similiar to this, but have still not found an answer. Basically for my database I need three tables but when creating my last table (race_schema) I get an error. "column "carid" referenced in foreign key constraint does not exist". I have tried various different things and edited the code, but nothing seems to work. Could anyone help me out?.
car_schema = """
carId VARCHAR NOT NULL,
PRIMARY KEY(carId)
"""
track_schema = """
trackId VARCHAR PRIMARY KEY NOT NULL,
trackLength INT NOT NULL,
lap_distance DECIMAL NOT NULL
"""
race_schema = """
raceId VARCHAR PRIMARY KEY NOT NULL,
FOREIGN KEY (carId) REFERENCES car(carId),
FOREIGN KEY (trackId) REFERENCES track(trackId),
lapIndex INT,
I am trying to create a user defined table type where I want to define a foreign key and unique key constraints but I'm unable to do so. Whenever I run the following I got the error "Incorrect syntax near the keyword 'CONSTRAINT'."
Please someone tell me what's wrong with the code?
create Type firstType as Table
(
firstId int IDENTITY (1,1)CONSTRAINT PK_firstId PRIMARY KEY CLUSTERED (firstId),
f_email varchar(200) CONSTRAINT AK_email UNIQUE(f_email) ,
fname varchar(100),
outId int CONSTRAINT FK_First FOREIGN KEY (outId) REFERENCES New(newId)
ON DELETE CASCADE
ON UPDATE CASCADE
)
A table type cannot have named constraints and cannot have foreign keys.
It may have only unnamed primary keys, unique keys and check constraints.
See https://learn.microsoft.com/en-us/sql/t-sql/statements/create-type-transact-sql?view=sql-server-ver15 for details.
You can use this instead:
CREATE Type firstType as Table
(
firstId int IDENTITY (1,1) PRIMARY KEY CLUSTERED (firstId),
f_email varchar(200) UNIQUE(f_email) ,
fname varchar(100),
outId int
)
cannot add foreign key constraint to table
create table users
(
user_id int auto_increment primary key not null,
username varchar(50) unique null ,
email varchar(50) unique ,
passwords varchar(50) not null,
login_status boolean not null
);
create table category (
category_id int primary key not null,
category_name varchar(50) not null
);
create table answers (
id_answer int auto_increment primary key not null,
answer boolean not null
);
create table questions (
question_id int primary key not null,
category_name varchar(50) not null,
content varchar(50) not null ,
foreign key (category_name) references category (category_name)
);
You get this error because there's no index on category_name in the category table. Change that CREATE statement as follows:
create table category (
category_id int primary key not null,
category_name varchar(50) not null,
KEY category_name_index (category_name)
);
From the docs (8.0 version, but the statement is true for older versions):
MySQL requires indexes on foreign keys and referenced keys so that foreign key checks can be fast and not require a table scan. In the referencing table, there must be an index where the foreign key columns are listed as the first columns in the same order. Such an index is created on the referencing table automatically if it does not exist. This index might be silently dropped later, if you create another index that can be used to enforce the foreign key constraint. index_name, if given, is used as described previously.
Also, you're using a varchar(50) as your foreign key, which is not usually a great idea for a variety of reasons. You probably want to use a numeric value, such as category_id, instead.
Is it possible to assign a foreign key to a json property in PostgreSQL? Here is an example what I would like to achieve, but it doesn't work:
CREATE TABLE Users (Id int NOT NULL PRIMARY KEY);
CREATE TABLE Data (
Id int NOT NULL PRIMARY KEY,
JsonData json NOT NULL, -- [{Id: 1, somedata: null},{Id: 2, somedata: null}, ...]
CONSTRAINT FK_Users_Data FOREIGN KEY (JsonData->Id) REFERENCES Users(Id) -- this constraint will fail
);
It is not possible, and may not ever be possible, to assign a foreign key to a json property. It'd be a major and quite complicated change to PostgreSQL's foreign key enforcement. I don't think it's impossible to do, but would face similar issues to those experienced by the foreign-keys-to-arrays patch.
With 9.4 it'll be possible to make a whole json object a foreign key as jsonb supports equality tests. In 9.3 you can't even do that.
Here's a little SPI function have_ids which I use for an integrity constraint on a one-to-many relationship with a jsonb column
CREATE TABLE foo (
id INTEGER NOT NULL
)
CREATE TABLE bar (
foo_ids pg_catalog.jsonb DEFAULT '[]'::jsonb NOT NULL,
CONSTRAINT bar_fooids_chk CHECK (have_ids ('foo', foo_ids))
)
With a couple of triggers on foo it's almost as good as a foreign key.
The foreign key parameter must be a column name:
http://www.postgresql.org/docs/current/static/sql-createtable.html
You will have to normalize
create table user_data (
id int not null primary key,
user_id int not null,
somedata text,
constraint fk_users_data foreign key (user_id) references Users(Id)
);
Yes it is possible but you will have to store another value. If you change your schema to:
CREATE TABLE Users (Id int NOT NULL PRIMARY KEY);
CREATE TABLE Data (
Id int NOT NULL PRIMARY KEY,
JsonData json NOT NULL,
UserId int generated always as ((JsonData->>'Id')::int) stored references Users(Id)
);
INSERT INTO Users VALUES (1);
Foreign key that doesn't exist:
INSERT INTO Data VALUES (1, '{"Id": 3}');
Returns the error:
ERROR: insert or update on table "data" violates foreign key constraint "data_userid_fkey" DETAIL: Key (userid)=(3) is not present in table "users".
Foreign key that does work:
INSERT INTO Data VALUES (1, '{"Id": 1}');