I have 2 tables:
Member Table:
Id - Primary key
Name
Age
Manager Table:
Id,
MemberId - FK
Title
How I can write a 1 to 0-1 relationship?
1 Member to 0-1 Manager
This is I am getting, why not showing 1--- 0 1
In order to create the tables for this relationship you need:
CREATE TABLE member(
Id int,
Name varchar,
Age int
Primary key(Id)
);
CREATE TABLE manager(
Id int,
MemberId int,
Title varchar,
Primary key(Id),
Foreign key(MemberId) References member(id)
);
Note: When you don't specify anything for the MemberId, this means it can be NULL. This means that there is no MemberId value for some managers.
Related
i have atable such as codes table have these values:
Major_code
minor_code
name
1
0
Country
1
1
USA
1
2
JOR
2
0
Food
2
1
Burger
2
2
Mansaf
I need to create table have these columns (ID, Country_ID , Food_ID) what is the best constraint that resolve this issue?
Having a single lookup table for all reference codes is a very poor design, to the point of almost being a SQL anti-pattern. It is likely to have performance issues. It is also difficult to ensure that the value of COUNTRY_MINOR_CODE references an actual country minor code in the reference table. Which brings us to this statement:
I need to create table have these columns (ID, Country_ID , Food_ID)
Can't be done. Or at least it can be done but you can't build foreign keys on that, because minor keys are not unique in the referenced table. But if you are set on a single table, say lookup_table with primary key defined on (major_code, minor code), you need this:
create table country_food (
id number primary_key
,country_major_code number not null
,country_minor_code number not null
,food_major_code number not null
,food_minor_code number not null
,constraint country_major_code_ck check (country_major_code = 1)
,constraint country_minor_code_ck check (country_minor_code != 0)
,constraint food_major_code_ck check (country_major_code = 2)
,constraint food_minor_code_ck check (country_minor_code != 0)
,constraint country_code_fk foreign key (country_major_code, country_minor_code) references lookup_table
,constraint food_code_fk foreign key (food_major_code, food_minor_code) references lookup_table
)
/
The hard coding of values, the additional check constraints, the increased complexity of joining to look up the name ... These are all reasons why you should choose to have separate tables for FOOD, COUNTRY, etc.
create table country (
country_id number primary_key
,country_name varchar2(24) not null
)
/
create table food (
food_id number primary_key
,food_name varchar2(24) not null
)
/
create table country_food (
id number primary_key
,country_id number not null
,food_id number not null
,food_major_code number not null
,constraint country_code_fk foreign key (country_id) references country
,constraint food_code_fk foreign key (food_id) references food
)
/
If I've got it right, you can get all Country+Food pairs with the query
select t1.minor_code counrty_id, t2.minor_code food_id
from (
select minor_code
from codesTable
where Major_code = (
select c.Major_code
from codesTable c
where c.minor_code=0 and c.name='Country')
) t1
cross join (
select minor_code
from codesTable
where Major_code = (
select c.Major_code
from codesTable c
where c.minor_code=0 and c.name='Food')
) t2
You can use the query to insert data into a table with an autogenerated ID or use it any other way.
First you need to consider the design of the tables
Table of country
Table of foods
Tables of food_country -------- relationship => many-to-many
CREATE TABLE Country
(
Major_code numeric(15) not null,
minor_code numeric(15),
name varchar(50),
CONSTRAINT country_pk PRIMARY KEY (Major_code)
);
CREATE TABLE Food
(
Food_ID numeric(15) not null,
//...........................
name varchar(50),
CONSTRAINT food_pk PRIMARY KEY (Food_ID)
);
CREATE TABLE Counry_Food
(
ID numeric(10) not null,
Country_ID numeric(15) not null,
Food_ID numeric(15) not null,
CONSTRAINT fk_country
FOREIGN KEY (Country_ID)
REFERENCES Country(Major_code),
CONSTRAINT fk_food
FOREIGN KEY (Food_ID)
REFERENCES supplier(Food_ID),
);
I have 4 tables:
User
create table user (
id int not null identity(1,1) primary key,
name varchar(30),
soyad varchar(50),
city varchar(30),
e_mail varchar(100),
pass varchar(10)
);
Category
create table category(
id int not null primary key,
name varchar(50)
);
Competition
create table competition(
id int primary key,
date date,
category_id int foreign key references category(id)
);
Competition_User
create table competition_user(
id int primary key,
competition_id int foreign key references competition(id),
joker_id int foreign key references joker(joker_id),
user_id int foreign key references user(id),
point int
);
I want write SQL code for this:
Write the SQL query, which will list which of the most competing members from each category got the highest score, in which category it competed, and how many questions are correct and how many questions are wrong.
I write this SQL query but failure:
SELECT category.id, user.id, count(competition_user.competition.id) AS competitioncount
FROM user, competition_user, competition, category
WHERE competition.id = competition_user.competition_id AND compettion.category_id = category.id AND user.id = competition.user_id
GROUP BY category.id, user.id
ORDER BY competitioncount desc
So I am working on a football world cup database. These are my important tables:
CREATE TABLE Countries(
Cid SERIAL PRIMARY KEY,
Name VARCHAR(256) NOT NULL UNIQUE
);
CREATE TABLE Stadiums(
Sid SERIAL PRIMARY KEY,
Name VARCHAR(256) NOT NULL UNIQUE,
Cid INT REFERENCES Countries NOT NULL
);
CREATE TABLE Groups(
Gid SERIAL PRIMARY KEY,
Name VARCHAR(64) NOT NULL,
TYear SMALLINT REFERENCES Tournaments NOT NULL
);
CREATE TABLE Teams(
Tid SERIAL PRIMARY KEY,
Cid INT REFERENCES Countries NOT NULL,
Gid INT REFERENCES Groups NOT NULL
);
CREATE TABLE Matches(
Mid INT PRIMARY KEY,
HomeTid INT REFERENCES Teams NOT NULL,
VisitTid INT REFERENCES Teams NOT NULL,
HomeScore SMALLINT NOT NULL,
VisitScore SMALLINT NOT NULL,
MatchDate DATE NOT NULL,
MatchType VARCHAR(64) NOT NULL,
Sid INT REFERENCES Stadiums NOT NULL
);
CREATE TABLE tempmatches(
year INTEGER,
host_country VARCHAR(255),
match_id INTEGER,
type VARCHAR(255),
date DATE,
location1 VARCHAR(255),
team1 VARCHAR(255),
team2 VARCHAR(255),
score1 INTEGER,
score2 INTEGER
);
so my current problem is that I need to populate the columns HomeTid and VisitId of the Matches table with the tid's from the team's table that corresponds with the country of that team from the countries table but I'm not sure how to do that. I tried a few queries but none of them seemed to work. Has anyone an idea on how to solve this?
Using JOIN keyword you can combine 2 tables data.
Here, in this case, you have to use 3-way join.
Eg:
3-way JOIN can be used in this way:
SELECT * FROM table1 JOIN table2 ON table1.col1=table2.col2 JOIN table3 ON table3.col3=table.col1;
Here the 2 tables will get joined based on the columns mentioned after the "ON" keyword.
Here is a reference link in which JOIN is explained clearly
https://www.w3schools.com/sql/sql_join.asp
Use JOIN operation. In SQL it helps to combine several tables(queries) in one
I am having this 3 table, which is available Trip , country , and location. the relation in my ERD design is
Location | M-1 | Country | 1-M | Available Trip
This is my attempt for the resolution
create table country
(
countryID int not null IDENTITY(1,1) PRIMARY KEY,
countryName varchar(50),
passportRegulation text,
currency varchar(20),
)
create table location
(
locationID int not null IDENTITY(1,1) PRIMARY KEY,
locationName varchar(100),
countryID int references country(countryID)on delete cascade
)
create table availableTrip
(
availableTripID int not null IDENTITY(1,1) PRIMARY KEY,
countryID int references country(countryID),
locationID int references location(locationID)
)
Is it possible to be correct if i having two foreign key to added into available trip , however i feel this is redundant because based on location i can know the country. I am kind of lost my direction for this design
Assuming that countryId needs to match the country in locationId, then you only want locationId in availableTrip.
You would look up the appropriate country using joins:
select avt.*, l.countryid
from availabletrip avt join
location l
on avt.locationid = l.locationid;
If the countryId could be different from the locationId, then you would want two columns.
I want to create a table which contains person, house and family, where only persons from the same family are allowed to live in the same house.
What I have so far does not work because I can only post one row with unique family and house. Is there any way to do this?
CREATE TABLE familyhouse (
person VARCHAR(64),
house VARCHAR(64),
family VARCHAR(64),
unique(house,family)
);
Example of correct table:
man,'1','1'
man2,'1','1'
man3,'1','1'
man4,'2','2'
man5,'2','2'
man6,'3','3'
Example of non-correct table:
man,'1','1'
man2,'1','1'
man3,'1','2'
I'd leverage the power of foreign keys and put the house and family in their own table (family_house) and a separate table for the residents.
CREATE TABLE family_house (
house VARCHAR(128) NOT NULL UNIQUE,
family VARCHAR(64) NOT NULL,
PRIMARY KEY (house, family)
);
CREATE TABLE residents (
person VARCHAR(64),
house VARCHAR(128),
family VARCHAR(64),
UNIQUE (person, house, family),
FOREIGN KEY (house, family) REFERENCES family_house
);
This way I can have multiple residents in the same home, but only one family to a home.
You can use a CHECK CONSTRAINT to maintain this:
CREATE TABLE familyhouse (
person VARCHAR(64),
house VARCHAR(64),
family VARCHAR(64)
);
CREATE FUNCTION CheckFamilyHouse(VARCHAR(64), VARCHAR(64))
RETURNS BOOLEAN AS $$
SELECT CASE WHEN EXISTS
( SELECT 1
FROM FamilyHouse
WHERE Family = $1
AND House != $2
)
THEN false
ELSE true
END
$$ LANGUAGE SQL;
ALTER TABLE familyHouse
ADD CONSTRAINT CHK_FamilyHouse
CHECK(CheckFamilyHouse(family, house));
With the above in place the second insert below will fail:
INSERT INTO familyhouse VALUES(1, 1, 1);
INSERT INTO FamilyHouse VALUES(2, 2, 1);
with the message:
ERROR: new row for relation "familyhouse" violates check constraint "chk_familyhouse": INSERT INTO FamilyHouse VALUES(2, 2, 1)
SQL Fiddle Example
create table house (
id serial primary key
);
create table family (
id serial primary key
);
create table house_family (
house_id integer,
family_id integer,
primary key (house_id, family_id),
foreign key (house_id) references house (id),
foreign key (family_id) references family (id)
);
create table person (
id serial primary key,
family_id integer,
house_id integer,
foreign key (house_id, family_id) references house_family (house_id, family_id)
);
insert into house values (1),(2),(3);
insert into family values (1),(2),(3);
insert into house_family values (1,1),(2,2),(3,3);
insert into person (family_id, house_id) values (1,1),(1,1);
select * from house;
id
----
1
2
3
select * from family;
id
----
1
2
3
select * from house_family;
house_id | family_id
----------+-----------
1 | 1
2 | 2
3 | 3
select * from person;
id | family_id | house_id
----+-----------+----------
5 | 1 | 1
6 | 1 | 1
Now if you try to insert a person from family_id 2 in the same house_of family_id 1:
insert into person (family_id, house_id) values (2,1);
ERROR: insert or update on table "person" violates foreign key constraint "person_house_id_fkey"
DETAIL: Key (house_id, family_id)=(1, 2) is not present in table "house_family".