some help here please with (advanced) mysql. Example illustrates the issue much better. So..
I have a predefined value pair table PARTNERS with partner1 and partner2 columns. And then there is another table PROJECTS which has partner1 and partner2 columns.
So, I want to select all PROJECTS where columns partner1 and partner2 are within the actual partners table described above.
Obviously, I cannot simply indicate "where partner1=... and/or partner2=..." because there would be no check of whether those two are partners (as defined in the PARTNERS table). (Just in case: there are projects with partner1 and partner2 not in the partner relationships.)
I don't think that kind of query is possible at all since it has the condition stored in the result. But would be happy if one can prove otherwise.
Thanks
It sounds like you need a query that will give you rows from PROJECTS where partner 1 and partner 2 are both the same as they are in any row in PARTNERS. So do an inner join:
SELECT * FROM projects
INNER JOIN partners
ON projects.partner1 = partners.partner1
AND projects.partner2 = partners.partner2
If you're up for restructuring your tables, it might make more sense to assign a unique ID to every row in PARTNERS, and use that ID in the PROJECTS table. That way instead of storing two columns of redundant data, you just have one column indicating which pair of students is on the project.
Related
I'm having trouble understanding joins and subqueries and when to use each. I'm sure that one of them is appropriate here.
I have a table ("owners") of (to keep things simple) unit numbers, names and email addresses.
I have another table ("widgets") of unit numbers and the number of widgets assigned to each unit. Each unit has 0, 1 or 2 widgets.
I need to send an email to each unit depending on whether they have 0, 1 or 2 widgets. In other words (and in plain English, not even remotely an attempt at semi-correct SQL):
select numwidgets from widgets where unit=x
then where owners.unit = widgets.unit
select unit, name, email
The data that I need to pass to my script will look like this:
unit name email widgets
1 Bob Smith bob#example.com 2
I can visualise in my mind the data that I need, but it's extracting it from two different tables that is the problem. The "owners" table is a permanent table, and the "widgets" table is a temporary one for tracking a specific issue that is being addressed in the email I'm sending. I don't need help sending the email, just creating the SQL I need to use to extract the data (numwidgets, name, email) for one email.
Thanks.
EDIT:
Input data:
owners table:
unit, name, email
1,Bob Smith, bob#example.com
widgets table:
unit,widgets
1,2
try this, a inner join selects all rows from both tables as long as there is a match between the columns in both tables.
Subqueries (also known as inner queries or nested queries) are a tool for performing operations in multiple steps. For example, if you wanted to take the sums of several columns, then average all of those values, you’d need to do each aggregation in a distinct step.
select owners.unit, name, email, widgets.numwidgets
from owners
inner join widgets On owners.unit = widgets.unit
where owners.unit = x
For your case you need an inner join. To understand that you need to see the concept of keys which is pretty simple.
In your tables unitnumber is the common column in both tables. So a join has to be applied based on this column.
Subqueries are used when the output of one query is given as input to another query i.e to perform related operations
Select o.unit,o.name,o.email ,w.numwidgets from owners o inner join widgets w on o.unit=w.unit where w.unit=X
In above query pass X = 0,1,2 as per the result you want
Thanks
I think you want:
select o.*, w.widgets
from owners o
inner join widget w
on o.unit = w.unit
where o.unit = 123;
I am trying to create a table that shows treatment information about patients (though I just wondered if would be better as a query) at a fictional hospital. The idea is that one row of this could be used to print an information sheet for the attending nurse(s).
I would like to make the attending_doctor column contain the name that corresponds with the employee_id.
|Patient_ID|Employee_ID|Attending_Doctor|Condition|Treatment|future_surgery|
Would appreciate any help. Thank you!
Just use a join in your query rather than have the employee name in 2 tables (which would mean updating in more than one location if they change name etc). For the sake of an example, this also gets the patients name from a 3rd table named patients.
eg
SELECT table1.*, employees.name, patients.name
FROM table1
LEFT JOIN employees ON employees.id = table1.employeeId
LEFT JOIN patients ON patients.id = table1.patientsId
Don't use directly this table, but build a view that contains the data you need. Then you can get the data from the view like it was a table.
Basically what you need is to have data in three tables. One table for patients, one table for for employees and one for the reports. Table with reports should contain only the employee_ID. Then you can either build a direct query over these three tables or build a view that will hide the complicated query.
I need to compile quantities from several warehouses that update their inventories periodically. The files are automatically loaded into tables in my MySQL database, but sometimes one warehouse might have a few more or less files than the others. I need to add them all to determine the total quantity available from the entire network.
My idea was to do:
SELECT
IFNULL(branch_01.qty,0) +
IFNULL(branch_02.qty,0) +
IFNULL(branch_03.qty,0) +
etc. through all warehouses joined as:
FROM branch_01
JOIN branch_02
USING (oespaced)
JOIN branch_03
USING (oespaced)
etc. through all warehouses
I can't use LEFT JOIN or RIGHT JOIN because sometimes one warehouse might have missing entries and sometimes another might. If a sku is missing from one branch's file, I'd prefer to still have the other branches added together, and just get a NULL, which would be converted to a 0 by the functions in the SELECT. When I've tested different joining solutions, I also seem to be getting Cartesian numbers of rows, which confuses me further.
Any guidance is greatly appreciated.
Just a little clarification:
We need to join 17 tables. We're not really concerned with the sum of a column, but more the individual values. For instance, a table might represent a list of items a,b,c,d, and list quantities of 1,2,3,4. We would have that table from several different warehouses and we would need to find a total for the entire network. If four warehouses had those values, we would want to see a,b,c,d with 4,8,12,16 as values for the total available.
I don't understand your question fully but hope my answer helps you a bit.
Are you joining many tables? So let's say 2 tables and you want to sum up the quantity column?
First of all, JOIN performs the cartesian product of 2(or more) tables. So you'll get so many instances that you don't wish to have; the solution to this is using the WHERE.
Maybe this is what you are looking for:
SELECT sum(a.qty) + sum(b.qty)
FROM table1 a, table2 b
WHERE a.pk = b.fk -- this one resolves the unwanted instances
fk denotes foreign key and pk denotes primary key.
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 have three tables: students, interests, and interest_lookup.
Students has the cols student_id and name.
Interests has the cols interest_id and interest_name.
Interest_lookup has the cols student_id and interest_id.
To find out what interests a student has I do
select interests.interest_name from `students`
inner join `interest_lookup`
on interest_lookup.student_id = students.student_id
inner join `interests`
on interests.interest_id = interest_lookup.interest_id
What I want to do is get a result set like
student_id | students.name | interest_a | interest_b | ...
where the column name 'interest_a' is a value in interests.name and
the interest_ columns are 0 or 1 such that the value is 1 when
there is a record in interest_lookup for the given
student_id and interest_id and 0 when there is not.
Each entry in the interests table must appear as a column name.
I can do this with subselects (which is super slow) or by making a bunch of joins, but both of these really require that I first select all the records from interests and write out a dynamic query.
You're doing an operation called a pivot. #Slider345 linked to (prior to editing his answer) another SO post about doing it in Microsoft SQL Server. Microsoft has its own special syntax to do this, but MySQL does not.
You can do something like this:
SELECT s.student_id, s.name,
SUM(i.name = 'a') AS interest_a,
SUM(i.name = 'b') AS interest_b,
SUM(i.name = 'c') AS interest_c
FROM students s
INNER JOIN interest_lookup l USING (student_id)
INNER JOIN interests i USING (interest_id)
GROUP BY s.student_id;
What you cannot do, in MySQL or Microsoft or anything else, is automatically populate columns so that the presence of data expands the number of columns.
Columns of an SQL query must be fixed and hard-coded at the time you prepare the query.
If you don't know the list of interests at the time you code the query, or you need it to adapt to changing lists of interest, you'll have to fetch the interests as rows and post-process these rows in your application.
What your trying to do sounds like a pivot.
Most solutions seem to revolve around one of the following approaches:
Creating a dynamic query, as in Is there a way to pivot rows to columns in MySQL without using CASE?
Selecting all the attribute columns, as in How to pivot a MySQL entity-attribute-value schema
Or, identifying the columns and using either a CASE statement or a user defined function as in pivot in mysql queries
I don't think this is possible. Actually I think this is just a matter of data representatioin. I would try to use a component to display the data that would allow me to pivot the data (for instance, the same way you do on excel, open office's calc, etc).
To take it one step further, you should think again why you need this and probably try to solve it in the application not in the database.
I know this doesn't help much but it's the best I can think of :(