I need to select the item name and the vendor name for each item that belongs to the vendor with a rating bigger than 4. And I can't find a way, I know it's something with joins but the 2 of them have the same column name.
CREATE TABLE venedors(
id int PRIMARY KEY,
name varchar2(20),
rating int)
CREATE TABLE items(
id int PRIMARY KEY,
name varchar2(20),
venedorId int references venedors(id))
If i understanded your problem.
Select items.name as itemName, venedors.name as vendorName
from items
inner join venedors
on items.venedorId = venedors.id
where venedors.rating > 4
If you want get all the vendors irrespective whether there are items associated with vendors or not, then try with left join as shown below:
Select v.name as vendorName, i.name as itemName
from venedors v
left join items i
on i.venedorId = v.id
where v.rating > 4
I have 3 tables:
CREATE table materials
(id serial primary key not null,
name varchar(50) not null,
unit varchar(10) not null default 'шт',
price decimal(12, 2) not null check (price>0));
CREATE table warehouses
(id serial primary key not null,
lastname varchar(25) not null);
CREATE table materials_in_warehouses
(id_warehouses integer references warehouses(id) on update cascade on delete cascade,
id_materials integer references materials(id),
unit varchar(15) default 'шт',
count integer not null CHECK (count>0),
lastdate date not null,
primary key (id_warehouses, id_materials);
And i need to select for each material : name; count of warehouses, where the material is present in an amount of > 100.
I tried to do something like this:
select materials.name, count(select * from materials_in_warehouses where
materials.id = materials_in_warehouses.id_materials AND material_in_warehouses.count > 100) as sount from materials;
But of course, this nonsense can't work.
Thank you in advance.
Pretty straight forward.
SELECT m.name, count(miw.id_warehouses)
FROM materials m
LEFT JOIN materials_in_warehouses miw ON m.id=miw.id_materials AND miw."count">100
GROUP BY m.id, m.name
Your mistake might have just been the fact that you're using count as a column name, when it's an aggregate function. Use double quotes in PostgreSql for that:
Escaping keyword-like column names in Postgres
Try like this
select materials.name, count(
select id_warehouses from materials_in_warehouses join materials
on materials.id = materials_in_warehouses.id_materials
where material_in_warehouses.count > 100
) as sount from materials;
SELECT m.name, COUNT(w.id) AS locs
FROM materials m, warehouses w, materials_in_warehouses mw
WHERE m.id = mw.id_materials
AND w.id = mw.id_warehouses
AND mw.count > 100
GROUP BY m.name;
If that works I'll come back and explain how I came up with it.
I am working on a project where I have a table of
all_names(
team_name TEXT,
member_name TEXT,
member_start INT,
member_end INT);
What I have been tasked with is creating a table of
participants(
ID SERIAL PRIMARY KEY,
type TEXT,
name TEXT);
which contains all team and member names as their own entries. Type may be either "team" or "member".
To compliment this table of participants I am trying to create a cross-reference table that allows a member to be referenced to a team by ID and vice versa. My table looks like this:
belongs_to(
member_id INT REFERENCES participants(ID),
group_id INT REFERENCES participants(ID),
begin_year INT,
end_year INT,
PRIMARY KEY (member_id, group_id);
I am unsure of how to proceed and populate the table properly.
The select query I have so far is:
SELECT DISTINCT ON (member_name, team_name)
id, member_name, team_name, member_begin_year, member_end_year
FROM all_names
INNER JOIN artists ON all_names.member_name = participants.name;
but I am unsure of how to proceed. What is the proper way to populate the cross reference table?
Probably the easiest solution is to use a few statements. Wrap this is a transaction to make sure you don't get concurrency issues:
BEGIN;
INSERT INTO participants (type, name)
SELECT DISTINCT 'team', team_name
FROM all_names
UNION
SELECT DISTINCT 'member', member_name
FROM all_names;
INSERT INTO belongs_to
SELECT m.id, g.id, a.member_start, a.member_end
FROM all_names a
JOIN participants m ON m.name = a.member_name
JOIN participants g ON g.name = a.team_name;
COMMIT;
Members that are part of multiple teams get all of their memberships recorded.
Suppose you had two tables. One called MOVIES:
MovieId
MovieName
Then another called ACTORS that contains people who appear in those movies:
MovieId
ActorName
Now, I want to write a query that returns any movie that contains ONE OR MORE of the following actors: "Tom Hanks", "Russell Crowe" or "Arnold Schwarzenegger".
One way to do it would be something like:
SELECT DISTINCT A.MovieId, M.MovieName FROM ACTORS A
INNER JOIN MOVIES M USING (MovieId)
WHERE A.ActorName IN ('Tom Hanks', 'Russell Crowe', 'Arnold Schwarzenegger');
Which is perfectly fine, however in my case I might have several more of these conditions on the WHERE clause so I want to find a way to make the MOVIES table the primary table I select from.
What's the best way to query for this? I'm using Oracle 11g if that matters, but I'm hoping for a standard SQL method.
You can use EXISTS or IN subqueries:
SELECT *
FROM MOVIES m
WHERE EXISTS
(
SELECT *
FROM ACTORS a
WHERE a.MovieId = m.MovieId
AND a.ActorName IN ('Tom Hanks', 'Russell Crowe', 'Arnold Schwarzenegger')
)
or
SELECT *
FROM MOVIES m
WHERE m.MovieId IN
(
SELECT a.MovieId
FROM ACTORS a
WHERE a.ActorName IN ('Tom Hanks', 'Russell Crowe', 'Arnold Schwarzenegger')
)
First you should have a 3rd table implementing the n:m relationship:
CREATE TABLE movie (
movie_id int primary key
,moviename text
-- more fields
);
CREATE TABLE actor (
actor_id int primary key
,actorname text
-- more fields
);
CREATE TABLE movieactor (
movie_id int references movie(movie_id)
,actor_id int references actor(actor_id)
,CONSTRAINT movieactor_pkey PRIMARY KEY (movie_id, actor_id)
);
Then you select like this:
SELECT DISTINCT m.movie_id, m.moviename
FROM movie m
JOIN movieactor ma USING (movie_id)
JOIN actor a USING (actor_id)
WHERE a.actorname IN ('Tom Hanks', 'Russell Crowe', 'Arnold Schwarzenegger');
Note, that text literals are enclose in single quotes!
I have a table where each row has a few fields that have ID's that relate to some other data from some other tables.
Let's say it's called people, and each person has the ID of a city, state and country.
So there will be three more tables, cities, states and countries where each has an ID and a name.
When I'm selecting a person, what's the easiest way to get the names of the city, state and country in a single query?
Note: I know this is possible with joins, however as there are more related tables, the nested joins makes the query hard to read, and I'm wondering if there is a cleaner way. It should also be possible for the person to have those fields empty.
Assuming the following tables:
create table People
(
ID int not null primary key auto_increment
,FullName varchar(255) not null
,StateID int
,CountryID int
,CityID int
)
;
create table States
(
ID int not null primary key auto_increment
,Name varchar(255) not null
)
;
create table Countries
(
ID int not null primary key auto_increment
,Name varchar(255) not null
)
;
create table Cities
(
ID int not null primary key auto_increment
,Name varchar(255) not null
)
;
With the Following Data:
insert into Cities(Name) values ('City 1'),('City 2'),('City 3');
insert into States(Name) values ('State 1'),('State 2'),('State 3');
insert into Countries(Name) values ('Country 1'),('Country 2'),('Country 3');
insert into People(FullName,CityID,StateID,CountryID) values ('Has Nothing' ,null,null,null);
insert into People(FullName,CityID,StateID,CountryID) values ('Has City' , 1,null,null);
insert into People(FullName,CityID,StateID,CountryID) values ('Has State' ,null, 2,null);
insert into People(FullName,CityID,StateID,CountryID) values ('Has Country' ,null,null, 3);
insert into People(FullName,CityID,StateID,CountryID) values ('Has Everything', 3, 2, 1);
Then this query should give you what you are after.
select
P.ID
,P.FullName
,Ci.Name as CityName
,St.Name as StateName
,Co.Name as CountryName
from People P
left Join Cities Ci on Ci.ID = P.CityID
left Join States St on St.ID = P.StateID
left Join Countries Co on Co.ID = P.CountryID
JOINS are the only way to really do this.
You might be able to change your schema, but the problem will be the same regardless.
(A City is always in a State, which is always in a Country - so the Person could just have a reference to the city_id rather than all three. You still need to join the 3 tables though).
There is no cleaner way than joins. If the fields are allowed to be empty, use outer joins
SELECT c.*, s.name AS state_name
FROM customer c
LEFT OUTER JOIN state s ON s.id = c.state
WHERE c.id = 10
According to the description of the schema that you have given you will have to use JOINS in a single query.
SELECT
p.first_name
, p.last_name
, c.name as city
, s.name as state
, co.name as country
FROM people p
LEFT OUTER JOIN city c
ON p.city_id = c.id
LEFT OUTER JOIN state s
ON p.state_id = s.id
LEFT OUTER JOIN country co
ON p.country_id = co.id;
The LEFT OUTER JOIN will allow you to fetch details of person even if some IDs are blank or empty.
Another way is to redesign your lookup tables. A city is always in a state and a state in a country. Hence your city table will have columns : Id, Name and state_id. Your state table will be : Id, Name and country_id. And country table will remain the same : Id and Name.
The person table will now have only 1 id : city_id
Now your query will be :
SELECT
p.first_name
, p.last_name
, c.name as city
, s.name as state
, co.name as country
FROM people p
LEFT OUTER JOIN city c
ON p.city_id = c.id
LEFT OUTER JOIN state s
ON c.state_id = s.id
LEFT OUTER JOIN country co
ON s.country_id = co.id;
Notice the difference in the last two OUTER JOINS
If the tables involved are reference tables (i.e. they hold lookup data that isn't going to change during the life time of a session), depending on the nature of your application, you could pre-load the reference data during you application start up. Then your query doesn't need to do the joins, instead it returns the id values, and in your application you do a decode of the ids when you need to display the data.
The easiest solution is to use the names as the primary keys in city, state, and country. Then your person table can reference them by the name instead of the pseudokey "id". That way, you don't need to do joins, since your person table already has the needed values.
It does take more space to store a string instead of a 4-byte pseudokey. But you may find the tradeoff worthwhile, if you are threatened by joins as much as you seem to be (which, by the way, is like a PHP programmer being reluctant to use foreach -- joins are fundamental to SQL in the same way).
Also there are many city names that appear in more than one state. So your city table should reference the state table and use these two columns as the primary key.
CREATE TABLE cities (
city_name VARCHAR(30),
state CHAR(2),
PRIMARY KEY (city_name, state),
FOREIGN KEY (state) REFERENCES states(state)
);
CREATE TABLE persons (
person_id SERIAL PRIMARY KEY,
...other columns...
city_name VARCHAR(30),
state CHAR(2),
country_name VARCHAR(30),
FOREIGN KEY (city_name, state) REFERENCES cities(city_name, state),
FOREIGN KEY (country_name) REFERENCES countries(country_name)
);
This just an example of the technique. Of course it's more complex than this, because you may have city names in more than one country, you may have countries with no states, and so on. The point is SQL doesn't force you to use integer pseudokeys, so use CHAR and VARCHAR keys where appropriate.
A disadvantage of standard SQL is the the return data needs to be in tabular format.
However some database vendors have added features that makes it possible to select data in non-tabular format. I don't know whether MySQL knows such features.
Create a view that does the Person, City, State, and Country joins for you. Then just reference the View in all other joins.
Something like:
CREATE VIEW FullPerson AS
SELECT Person.*, City.Name, State.Name, Country.Name
FROM
Person LEFT OUTER JOIN City ON Person.CityId = City.Id
LEFT OUTER JOIN State ON Person.StateId = State.Id
LEFT OUTER JOIN Country ON Person.CountryId = Country.Id
Then in other queries, you can
SELECT FullPerson.*, Other.Value
FROM FullPerson LEFT OUTER JOIN Other ON FullPerson.OtherId = Other.Id
All great answers but the questioner specified they didn't want to use joins. As one respondent demonstrated, assuming your Cities, States, and Countries tables have an Id and a Description field you might be able to do something like this:
SELECT
p.Name, c.Description, s.Description, ct.Description
FROM
People p, Cities c, States s, Countries ct
WHERE
p.Id = value AND
c.Id = value AND
s.Id = value AND
ct.Id = value;
Joins are the answer. With practise they will become more readable to you.
There may be special cases where creating a function would help you, for example you could do the following (in Oracle, I don't know any mysql):
You could create a function to return a formatted address given the city state and country codes, then your query becomes
SELECT first_name, last_name, formated_address(city_id, state_id, country_id)
FROM people
WHERE some_where_clause;
where formated_address does individual lookups on the city state and country tables and puts separators between the decoded values, or returns "no address" if they are all empty, etc