OK lets consider we have the following db shema:
ConstructionPlans
c_id
Part
p_id
PlanPart
c_id p_id
The Table Construction Plans has all the plans, Part has all the parts and PlanPart has an entry for every plan and part combination. I am trying to think of a query considering that you would want to get all the construction plans (literally all) and have them in order of the number of parts that are missing. I have all the parts I have in an array for this query. I would also like to be able to check all the missing parts for a plan later on (but I guess one would simply take alle the c_ids in PlanPart and substract with the other Query and a Where Clause with the parts one already has).
Thank you for your input :)
Assuming that you have a column quantity in your Part table and a coulmn name in you ConstructionPlan table
select p.p_id from Part p, PlanPart pp, ConstructionPlan cp where p.quantity=0 and p.p_id=pp.p_id and cp.c_id = pp.c_id and cp.name = '<your plan name goes here>'
Related
I have a MySQL database with a table for products and a table with the buying/selling history of these products. The buying and selling history of each product is basically tracked in this history table.
I am looking for the most efficient way of creating a list of these products with the earliest transaction data from the history table joined.
At the moment my SQL query selects the products with the earliest history entry like this:
SELECT p.*
, h.transdate
, h.sale_price
FROM products p
LEFT
JOIN
( SELECT MIN(transdate) transdate
, product_id
FROM history
GROUP
BY product_id
) hist_min
ON hist_min.product_id = p.id
LEFT
JOIN history h
ON h.product_id = hist_min.product_id
AND h.transdate = hist_min.transdate
Since this query is used very frequently and potentially with many products I am considering storing the first sale_price directly in the 'products' table. This way I wouldn't need the 2 additional JOINS at all. But this would mean I store redundant data.
For me the most important question is, which of these possibilities is the most efficient one.
I am not sure if I am allowed to ask this additionally, but if there is an even better way I would like to know about it.
EDIT: To clarify 'efficient', I am talking about tens of thousands of products with maybe 10 history records each, where I only pick pagewise 20 with a LIMIT statement. To save the original price with the product would be pulling the data straight with the record, while the scanning of dates in the history table for the earliest time and another scan to join the actual row of data would require certainly more resources, even if only for the second table involved. The use of a primary key ID oder an index over product_id and transdate would certainly speed up the second join though.
What you're describing is called 'normalization'. The level of normalization is not a black and white area so I don't think this site is the place to get your answer as it's primarily opinion based.
Check out these links to get started:
Database Normalization Explained in Simple English
Wikipedia (check out the 'See also' section, it describes level of normalization)
I have two tables - books and images. The books table has many columns - including id (primary key), name (which is not unique), releasedate, etc. The images table have two columns - id (which is not unique, i.e one book id may have multiple images associated with it, and we need all those images. This column has a non-unique index), and poster (which is unique primary key, all images lie in the same bucket, hence cannot have duplicate names). My requirement is given a book name, find all images associated with it (along with the year of release and the bucketname for each image, the bucketname being just a number in this case).
I am running this query:
select books.id,poster,bucketname,year(releasedate) from books
inner join images where images.bookId = books.id and books.name = "<name>";
A sample result set may look like this:
As you can see there are two results matching - one with id 2 and year 1989, having 5 images, other one with id 261009, year 2013 and one image.
The problem is, the query is extremely slow. It takes around .14 seconds from MySQL console itself, under zero load (in production there may be several concurrent requests and they may be queued, leading to further delay), which is unacceptable for autocomplete. Can anyone tell me how to optimize the query by adding correct indices/keys to the tables? If it is not possible from MySQL, suggestions regarding a proper Redis schema would be useful as well.
Edit: Approx no. of rows in images - 480k, in books - 285k. In future, autocomplete will show result for book authors as well as book names, hence the query will need to expand to take into account a separate table authors where each author will have an id and name, just like a book.
For optimal performance, you want suitable covering indexes available. For example:
... on `books` (`name`,`id`,`releasedate`)
... on `images` (`bookid`,`poster`,`bucketname`)
We want name as the leading column in the index, because of the equality predicate in the WHERE clause. We want id and releasedate also included in the index to make it a "covering index", so the query can be satisfied from the index, without a need to visit pages of the underlying table to retrieve values.
We want bookid as the leading column because of the reference in the ON clause. Again, having poster and bucketname available right in the index make it a "covering" index.
Use EXPLAIN to see the query execution plan.
Also, note that the inner join operation won't return a row from books if a matching row in images is not found. If we want to return a row from books even when no image is available, we could use an outer join.
I'd write the query like this:
SELECT b.id
, i.poster
, i.bucketname
, YEAR(b.releasedate)
FROM books b
LEFT
JOIN images i
ON i.bookid = b.id
WHERE b.name = ?
Here is my Database structure (basic relations):
I'm attempting to formulate a one-line query that will populate the clients_ID, Job_id, tech_id, & Part_id and return back all the work orders present. Nothing more nothing less.
Thus far I've struggled to generate this Query:
SELECT cli.client_name, tech.tech_name, job.Job_Name, w.wo_id, w.time_started, w.part_id, w.job_id, w.tech_id, w.clients_id, part.Part_name
FROM work_orders as w, technicians as tech, clients as cli, job_types as job, parts_list as part
LEFT JOIN technicians as techy ON tech_id = techy.tech_name
LEFT JOIN parts_list party ON part.part_id = party.Part_Name
LEFT JOIN job_types joby ON job_id = joby.Job_Name
LEFT JOIN clients cliy ON clients_id = cliy.client_name
Apparently, once all the joining happens it does not even populate the correct foreign key values according to their reference.
[some values came out as the actual foreign key id, not even
corresponding value.]
It just goes on about 20-30 times depending on largest row of a table that I have (one of the above).
I only have two work orders created, So ideally it should return just TWO Records, and columns, and fields with correct information. What could I be doing wrong? Haven't been with MySQL too long but am learning as much as I can.
Your join conditions are wrong. Join on tech_id = tech_id, not tech_id = tech_name. Looks like you do this for all your joins, so they all need to be fixed.
I really don't follow the text of your question, so I am basing my answer solely on your query.
Edit
Replying to your comment here. You said you want to "load up" the tech name column. I assume you mean you want tech name to be part of your result set.
The SELECT part of the query is what determines the columns that are in the result set. As long as the table where the column lives is referenced in the FROM/JOIN clauses, you can SELECT any column from that table.
Think of a JOIN statement as a way to "look up" a value in one table based on a value in another table. This is a very simplified definition, but it's a good way to start thinking about it. You want tech name in your result set, so you look it up in the Technicians table, which is where it lives. However, you want to look it up by a value that you have in the Work Orders table. The key (which is actually called a foreign key) that you have in the Work Orders table that relates it to the Technicians table is the tech_id. You use the tech_id to look up the related row in the Technicians table, and by doing so can include any column in that table in your result set.
I am trying to query a database to return some matching records and can't work out how to do it in the most efficient way. I have a TUsers table, a TJobsOffered table and a TJobsRequested table. The UserID is the primary key for the TUsers table and is used within the Job tables in a one to many relationship.
Ultimately I want to run a query that returns a list of all matching users based on a particular UserID (eg a matching user is one that has at least one matching record in both tables, eg if UserA has jobid 999 listed in TJobsOffered and UserB has jobid 999 listed in TJobsRequested then this is a match).
In order to try and get my head around it i've simplified it down a lot and am trying to match the records based on the jobids for the user in question, eg:
SELECT DISTINCT TJobsOffered.FUserID FROM TJobsOffered, TJobsRequested
WHERE TJobsOffered.FUserID=TJobsRequested.FUserID AND
(TJobsRequested.FJobID='12' OR TJobsRequested.FJobID='30') AND
(TJobsOffered.FJobID='86' OR TJobsOffered.FJobID='5')
This seems to work fine and returns the correct results however when I introduce the TUsers table (so I can access user information) it starts returning incorrect results. I can't work out why the following query doesn't return the same results as the one listed above as surely it's still matching the same information just with a different connector (or is the one above effectively many to many and the one below 2 sets of one to many comparisons)?
SELECT DISTINCT TUsers.Fid, TUsers.FName FROM TUsers, TJobsOffered, TJobsRequested
WHERE TUsers.Fid=TJobsRequested.FUserID AND TUsers.Fid=TJobsOffered.FUserID AND
(TJobsRequested.FJobID='12' OR TJobsRequested.FJobID='30') AND
(TJobsOffered.FJobID='86' OR TJobsOffered.FJobID='5')
If anyone could explain where i'm going wrong with the second query and how you should incorporate TUsers then that would be greatly appreciated as I can't get my head around the join. If you are able to give me any pointers as to how I can do this all in one query by just passing the user id in then that would be massively appreciated as well! :)
Thanks so much,
Dave
Try this
SELECT DISTINCT TJobsOffered.FUserID , TUsers.FName
FROM TJobsOffered
INNER JOIN TJobsRequested ON TJobsOffered.FUserID=TJobsRequested.FUserID
LEFT JOIN TUsers ON TUsers.Fid=TJobsOffered.FUserID
WHERE
(TJobsRequested.FJobID (12,30) AND
(TJobsOffered.FJobID IN (86 ,5)
You need to add "AND TJobsOffered.FUserID=TJobsRequested.FUserID" to your where clause.
We're hiring some third party Test engineers and programmers to help us with some bugs on our website. They would be working on a beta installation of our web application. The thing is that we need to give them a copy of our database, we don't want to give the entire database, its a huge database of companies. So we would want to give them a watered down version of it that has less than a fraction of the actual data -- just enough for making a proper test.
We have data in the following Schema:
COMPANIES
ID|NAME|CATEGORY|COUNTRY_ID.....
We also have a set number of categories and countries.
The thing is that we don't want the deletion to be too random, basically out of the hundreds of thousands of entries we need to give them a version that has a few hundred entries but such that, you have at least 2-3 companies for each country and category.
I'm a bit perplexed as how to do a select query with the above restriction much less delete.
It's a MySQL database we would be using here. Can this be even done in SQL or do we need to make a script in php or so?
Following select statement will select companies with first 3 id in ascending order for each category, country_id combination:
select id, name, category, country_id
from companies c1
where id in (
select id
from companies c2
where c2.category=c1.category and c2.countr_id=c1.country_id
order by id
limit 3
);
Not sure my answer will fit your needs since I am doing some assumptions that may be wrong, but you could try the following approach:
select category, country_id, min(id) id1, max(id) id2
from companies
group by country_id, category
order by country_id, category
This query only gives you 2 company ids instead of 3 and they will be the first and last id that match category and country.
Please note also I wrote this out of my mind and have no MySQL engine to test it.
Hope that helps or at least gives you a hint on how to do it.