I haven't been able to figure out how to make this query work.
I have a table for people and their personal data.
I have a table of let's call it houses
Let's say that the tables have these fields:
PEOPLE
id, code, name, lastname
HOUSES
id, codeowner, codeintermediate, codebuyer, area, numberofrooms
If I have three columns with a relationship with the same table (people) how can I make a LEFT JOIN work?
If owners, intermediates and buyers were separated I would use something like
"SELECT
houses.*,
owners.name AS ownersname,
intermediates.name AS intermediatesname,
buyers.lname AS buyersname
FROM houses
LEFT JOIN owners ON houses.codeowner = owners.code
LEFT JOIN intermediates ON houses.codeintermediate = intermediates.code
LEFT JOIN buyers ON houses.codebuyer = buyers.code
But how can I make this work with a single PEOPLE table? How can I use the aliases and so? Thank you beforehand!
Join the people table 3 times
SELECT
houses.*,
owners.name AS ownersname,
intermediates.name AS intermediatesname,
buyers.name AS buyersname
FROM houses
LEFT JOIN people as owners ON houses.codeowner = owners.code
LEFT JOIN people as intermediates ON houses.codeintermediate = intermediates.code
LEFT JOIN people as buyers ON houses.codebuyer = buyers.code
Related
I am trying to create views of a database containing information about horses, more specifically horses, their owners, and the horse boarder. The view must join three tables. I have to create a view of "first name, last name, primary phone, and barnname". Then I have to join tables "boarder, horse, and boarder_horse" to create the relationship. I can't figure out how to connect the various tables together.
So far, this is what I have:
CREATE VIEW horse_owner
AS
SELECT b.boarder firstname, b.boarder lastname, b.boarder primaryphone,
h.horse barname
FROM boarder b
INNER JOIN horse h
ON bh.horse_id = h.id
INNER JOIN boarder_horse
ON bh.boarder_id = b.id
ORDER BY LastName DESC;
I don't understand how to correctly link the appropriate tables together.
You had order of JOINs wrong. Also, you were missing alias bh. Try:
CREATE VIEW horse_owner
AS
SELECT b.firstname, b.lastname, b.primaryphone,
h.barname
FROM boarder b
INNER JOIN boarder_horse bh
ON bh.boarder_id = b.id
INNER JOIN horse h
ON bh.horse_id = h.id
ORDER BY LastName DESC;
I have three tables, the first two are used to store information about people.
So how do I add the date to the link the 3 tables?
Trying to practice my school work at home and have no idea how to do this!
Edit: all I can think off would be this SELECT B.Date_of_exams, C.last_name, B.subjects_name
If I understand what you want, you need to join the tables using INNER JOIN like this:
SELECT B.Date_of_exams, C.last_name, B.subjects_name
FROM
entries A
INNER JOIN subjects B
ON A.subjects = B.subjects_id
INNER JOIN students C
ON A.student = C.student_id
I need to do a query on the same field on a MySQL table but with different parameters. This is my query. The issue that comes up is that MySQL is saying that users_name is ambiguous.
SELECT projects_id,
projects_users_id,projects_companies_id,projects_name,
projects_description,project_registered_date,
projects_users_id_register,
users.users_name as userInCharge,companies.companies_name as company,
users.users_name as user_register FROM projects
LEFT JOIN users as userInCharge ON (users_id = projects_users_id)
LEFT JOIN users as register ON (users_id=projects_users_id_register)
LEFT JOIN companies ON (companies_id = projects_companies_id) ORDER BY projects_id DESC
My goal is to get the ID of both the person in charge of the project and the person who registered the project. How do I do this?
Your ambiguity is arising because of these LEFT JOIN clauses:
LEFT JOIN users as userInCharge ON (users_id = projects_users_id)
LEFT JOIN users as register ON (users_id=projects_users_id_register)
You need to specify where users_id is coming from (yes - I know they're from the same table, but SQL is a bit slow sometimes) Try:
LEFT JOIN users as userInCharge ON (userInCharge.users_id = projects_users_id)
LEFT JOIN users as register ON (register.users_id=projects_users_id_register)
Use the table alias and not users.users_name.
And also in the joins.
You JOIN with users table as userInCharge and register so use these names when You specify columns
userInCharge.users_name as userInCharge
register.users_name as user_register
instead of
users.users_name as userInCharge
users.users_name as user_register
I have a printed table here, and I issue a query to attempt to join the tables where the Tech_id, clients_id, job_id, part_id should populate with corresponding key in their tables / column too.
Here is my query:
SELECT * FROM work_orders, technicians as tech, parts_list as parts, job_types as job, clients as client
LEFT JOIN technicians ON tech_id = technicians.tech_name
LEFT JOIN parts_list ON part_id = parts_list.Part_Name
LEFT JOIN job_types ON job_id = job_types.Job_Name
LEFT JOIN clients ON clients_id = clients.client_name
I've messed around with multiple different variations, this one seem to be syntax correct, but now I'm getting: Column 'clients_id' in on clause is ambiguous
I'm sure that it will happen for not only clients but maybe others. I want to be able to print the table as in the picture above, but with the clients listed. Is it possible to be done via one query as well? thanks.
You have two problems.
First (this might not be your problem, but that's a "good practice"), you shouldn't use SELECT *, as you could indeed have a field with same name in different tables.
This is one (of the many) good reason to avoid * in a Select clause.
Then, your main problem is that you select tables in your from clause, and then again by joining.
Problematic line :
FROM work_orders, technicians as tech, parts_list as parts, job_types as job, clients as client
So (I don't know your table structure, so they may be errors, but you've got the idea)
SELECT
w.client_id,
t.tech_name
--etc
FROM work_orders w
LEFT JOIN technicians t ON c.tech_id = t.tech_name
LEFT JOIN parts_list p ON c.part_id = p.Part_Name
LEFT JOIN job_types j ON w.job_id = j.Job_Name
LEFT JOIN clients c ON w.clients_id = c.client_name
This means that clients_id exists in multiple tables. You need to specify which one you want. So if you for example want the clients_id of the clients table, do SELECT clients.clients_id
If all the fiels listed in your question are in the clients table you could do:
SELECT clients.* FROM work_orders, technicians as tech, parts_list as parts, job_types as job, clients as client
LEFT JOIN technicians ON tech_id = technicians.tech_name
LEFT JOIN parts_list ON part_id = parts_list.Part_Name
LEFT JOIN job_types ON job_id = job_types.Job_Name
LEFT JOIN clients ON clients_id = clients.client_name
I have data related as follows:
A table of Houses
A table of Boxes (with an FK back into Houses)
A table of Things_in_boxes (with an FK back to Boxes)
A table of Owners (with an FK back into Houses)
In a nutshell, a House has many Boxes, and each Box has many Things in it. In addition, each House has many Owners.
If I know two Owners (say Peter and Paul), how can I list all the Things that are in the Boxes that are in the Houses owned by these guys?
Also, I'd like to master this SQL stuff. Can anyone recommend a good book/resource? (I'm using MySQL).
Thanks!
Peter and Paul are gay couple ?
Then you should go for many-to-many relationship instead of having ownerID inside of Houses Table
ie. Houses2Owners with two columns ownerID and houseID
then the query would be
select item from houses as h
left join Boxes as b on h.houseID=b.houseID
left join Things as t on b.boxID=t.boxID
left join Houses2Owners as h2o on h.houseID=h2o.houseID
left join Owners as o on h2o.ownerID=o.ownerID
Main question you should ask yourself while designing that would be whether each object will appear once ie. if there are two similar boxes with similar things in them or ie. two boxes with ski masks in them.
Then you should create tables with no relationship to parent object and also to create a table that connects two tables. This way you will avoid ski mask to appear twice for two boxes which contain that mask.
SELECT
Things_in_boxes.*
FROM
Houses
JOIN Boxes ON Houses.HouseID = Boxes.House
JOIN Things_in_boxes ON Boxes.BoxID = Things_in_boxes.Box
WHERE
Houses.Owner = 'Peter' OR Houses.Owner = 'Paul'
As for resources to learn from... I can't really suggest anything specific. I learnt how to use (My)SQL gradually and from a number of sources, and can't single any of them out as having been of primary importance. w3schools has OK coverage of the very basic stuff, and MySQL's own documentation (available on the web, google for it) does an OK job and is a reasonable reference for when you want to know the nitty gritty of some topic or other.
EDIT: The above answer is wrong. I had missed the stipulation that a House can have multiple Owners.
New approach: I'll assume that there is a cross-referencing table, HouseOwners, with House and Owner as foreign keys.
My first thought was this:
SELECT
Things_in_boxes.*
FROM
Houses
JOIN Boxes ON Houses.HouseID = Boxes.House
JOIN Things_in_boxes ON Boxes.BoxID = Things_in_boxes.Box
JOIN HouseOwners ON Houses.HouseID = HouseOwners.House
WHERE
HouseOwners.Owner = 'Peter' OR HouseOwners.Owner = 'Paul'
However, this is not quite right. If both Peter and Paul are Owners of a given house, then the things in the boxes in that house would show up twice. I think a subquery is needed.
SELECT
Things_in_boxes.*
FROM
Houses
JOIN Boxes ON Houses.HouseID = Boxes.House
JOIN Things_in_boxes ON Boxes.BoxID = Things_in_boxes.Box
WHERE
Houses.HouseID IN (
SELECT DISTINCT House
FROM HouseOwners
WHERE Owner = 'Peter' OR Owner = 'Paul'
) AS MySubquery
SELECT t.name
FROM Houses h
INNER JOIN Boxes b ON b.houseId = h.id
INNER JOIN Things t ON t.boxId = b.id
INNER JOIN Owners o ON o.houseId = h.id
WHERE o.name = 'Peter' OR o.name = 'Paul'
By using inner joins you can combine these 4 tables with all the linked information. There is also an other way using inner select queries:
SELECT t.name
FROM Houses h
INNER JOIN Boxes b ON b.houseId = h.id
INNER JOIN Things t ON t.boxId = b.id
INNER JOIN Owners o ON o.houseId = h.id
WHERE h.id IN (SELECT o.housId
FROM Owners o
WHERE o.name = 'Peter' OR o.name = 'Paul')
This query works differently (by first finding the two house ID's of Peter and Paul and then performing the join), but it has the same effect.
Hopefully these examples will help you understand SQL :)
This isn't tested and written on the spot:
SELECT *
FROM
`things_in_boxes` AS a
LEFT JOIN `houses` AS b
on ( a.`house_id` = b.`house_id` )
LEFT JOIN `owners` AS c
on ( b.`house_id` = c.`house_id` )
WHERE c.`owner_id` IN( 0, 1 )
That is the general structure I would use, where the "0, 1" in the last IN statement are the owner ids for Peter and Paul. If you wanted to do it by name, you could simply make it something like
c.`name` IN( 'Peter', 'Paul' )
As far as books, I can't really tell you, I've learned through tutorials and references.
Here's one approach:
SELECT * FROM Things_in_boxes t
WHERE box_id IN (
SELECT b.id
FROM Boxes b
INNER JOIN Owners o
ON (o.house_id = b.house_id)
WHERE o.name LIKE 'Peter'
OR o.name LIKE 'Paul'
)
Note that you don't need to join on the House table, since both the Boxes and Owners have a house id.
Without knowing the full structure, I will assume a structure to build a query, step by step
Get the IDs of the houses belonging to the owners
select id from House where owner in ('peter', 'paul')
Get the boxes in those houses
select boxid from boxes where homeid in (select id from House where owner in ('peter', 'paul'))
Get the things in those boxes
select * from things where boxid in (select boxid from boxes where homeid in (select id from House where owner in ('peter', 'paul')))
This should get you what you want, but is very inefficient.
In the above method, The final query in step 3 gets the ids in each step, and stores them in temporary storage while it consumes them. This is a very slow operation in most DBMS.
The better alternative is a join. Combine all the tables and select the desired data.
select * from things join boxes on things.boxid =boxes.boxid join houses on boxes.houseid=house.id join owners on houses.owner=owner.ownerid where owner.name in ('peter',''paul)