I'm trying to join a few tables in MySQL. Our setup is a little unique so I try to explain as good as I can.
I have a table 'INVENTORY' that represents the current items on stock.
These items are stored in a table 'COMPONENT'
Components are being used in installations.
Every user can have multiple installations and the same component can be used in multiple installation as well.
To uniquely map a component to an installation, it can be assigned to a PRODUCT. a product as has a 1-1 relationship with an installation. A component is not directly related to an installation
To finally assign a product to a specific installation a mapping table COMPOMENT_PRODUCT is used.
Example:
A component is like a part, lets say a screw. This screw is used in a computer. The very same screw can be used on multiple computers. But each computer can only be used on one specific installation.
TABLE COMPOMENT_PRODUCT
COMPOMENT_ID PRODUCT_ID
1 1
1 2
2 1
2 2
So we have the components C1 and C2 relevant for two installations.
TABLE INVENTORY
COMPOMENT_ID INSTALLATION_ID ON_STOCK
1 1 5
1 2 2
What I want to achieve
Now, I want to retrieve the inventory state for all components. But, not every component has an inventory record. In these cases, the ON_STOCK value from the inventory shall be NULL
That means, for this example I'd expect the following results
COMPOMENT_ID PRODUCT_ID ON_STOCK
1 1 5
1 2 2
2 1 NULL
2 2 NULL
But executing this query:
SELECT DISTINCT
COMPONENT_PRODUCT.COMPONENT_ID,
COMPONENT_PRODUCT.PRODUCT_ID,
INVENTORY.ON_STOCK
FROM INVENTORY
RIGHT JOIN COMPONENT_PRODUCT ON COMPONENT_PRODUCT.COMPONENT_ID =
INVENTORY.COMPONENT_ID
returns the following resultset:
COMPONENT_ID PRODUCT_ID ON_STOCK
1 1 5
1 2 5
1 1 2
1 2 2
2 1 (null)
2 2 (null)
Now, my next thought was, "of course, this is how joins behave, okay I need to group the results". But the way SQL works, the aggregation is not entirely predictable. SO when I
GROUP BY COMPONENT_PRODUCT.COMPONENT_ID,COMPONENT_PRODUCT.PRODUCT_ID
I get this result:
COMPONENT_ID PRODUCT_ID ON_STOCK
1 1 5
1 2 5
2 1 (null)
2 2 (null)
I have prepared a Fiddle here: http://sqlfiddle.com/#!9/71ca87
What am I forgetting here? Thanks in advance for any pointers.
Try this query -
SELECT DISTINCT
COMPONENT_PRODUCT.COMPONENT_ID,
COMPONENT_PRODUCT.PRODUCT_ID,
INVENTORY.ON_STOCK
FROM INVENTORY
RIGHT JOIN COMPONENT_PRODUCT ON COMPONENT_PRODUCT.COMPONENT_ID =
INVENTORY.COMPONENT_ID
AND COMPONENT_PRODUCT.PRODUCT_ID = INVENTORY.INSTALLATION_ID
Related
I have searched many other questions, but cant find a usable comparison. I have a SQL table that has a list of all the rooms at our hotel. I want to know the next time each room is going to be occupied. There are two tables I am looking at, one contains the name and details of each room we have, for all intents it is a static table. The other table is a reservations table that shows check in and check out times, and has a column that references which room is being used.
Table Rooms
unique id name
1 Room 3
2 Room 4
3 Suite 1
4 Suite 2
5 Suite 3
Table Reservations
unique id start date room id
1 12/4/16 3
2 12/4/16 4
3 12/6/16 3
4 12/12/16 3
5 12/14/16 2
6 12/20/16 2
This would return only 3 values:
2 12/20/16
3 12/4/16
4 12/4/16
If also possible I would like the make it so that if a reservation is not found a null value is returned, so ultimately, the return value would be
Room Next Occurrence
1 null
2 12/20/16
3 12/4/16
4 12/4/16
5 null
Is there a way of doing this without my current php hack that runs 200 sql queries?
Thanks so much!
You can use left join
select rooms.id, rooms.name, reservations.`start date`
from Rooms
left join reservations on reservations.`room id` = Rooms.id
order by rooms.id
I am designing a mysql database and have come across these relations which will grow in the future.
Suppose Customer is tied to 2 different tables Policies and Options.
Each customer has multiple relationship with policies and likewise with options. Since I am keeping a details and history of the table as well every time I add a relation with customer, I will have to maintain another 2 tables. To calculate the price the customer owes, I will have to go thru customer_policies then customer_options and calculate the total price. Also the number of tables increases as the relationship increases.
If customer has a relation with policies it will have 2 tables -
customer_policies and customer_policies_details.
If customer has one more relation with options, it will add 3 more -
customer_options, and customer_option_history.
Like wise, it will keep on adding 2 more tables if there is one more
relation and the problem grows and grows.
I have tried 2 different options which I have mentioned below. I wanted to know what is the best way to solve this problem so that the table can be maintained as the relation grows.
Option 1:
customer_policies:
CustomerPolicyId CustomerId PolicyId Status
1 1 1 Active
2 1 2 Active
customer_policies_details:
CustomerPolicyDetailsId CustomerPolicyId Price
1 1 10
2 2 20
customer_options:
CustomerOptionId CustomerId OptionId Status
1 1 1 Active
2 1 2 Active
customer_options_details:
CustomerOptionDetailsId CustomerOptionId Price
1 1 10
2 2 20
Option 2:
Create a single table customer_selections and use Type and Id field instead like so:
customer_selections:
CustomerSelctionId CustomerId Type Id Status
1 1 Policy 1 Active
2 1 Policy 2 Active
3 1 Option 1 Active
4 1 Option 2 Active
customer_selection_details:
DetailsId CustomerSelctionId Price
1 1 10
2 2 20
3 3 10
4 4 20
To create a history of this I just have to create a customer_selections_details and keep track of all changes.
There should be better ways to solve this problem.
I am pretty new to mysql and this site. I got an old mysql database (100.000 entries) to migrate to our new system. This is the old table:
CUSTOMER
Customer_ID Name Categories
1 Bob 1,2
2 Phil NULL
3 Ines 10,8
4 Carol 1
5 Rick 13,2
And i need the following structure:
CUSTOMER
Customer_ID Name
1 Bob
2 Phil
3 Ines
4 Carol
5 Rick
Category
Category_ID Category_Name
1 Biker
2 Doctors
3 Teacher
... ...
13 Drivers
CustomerHasCategory
Customer_ID Category_ID
1 1
1 2
3 10
3 8
4 1
5 13
5 2
Thanks for any help.
I also had this problem but not in MySQL. I solved it with Python using the Pandas library. So, the exact steps I followed won't be useful for you. However, I'll show you the general idea behind the solution I used.
Below is image of the original column
First, I splitted the text into columns using the comas as the delimiter.
Next, I 'stacked' the columns
Finally, I removed the artefact column(s). So, I have only the ID and the values columns. This creates a one-to-many relationship.
I need to filter a table in mysql but can't get past the beginning.
The table has 2 fields:
ID_house house_feature
1 1
1 2
1 4
1 5
2 1
2 3
2 4
3 1
3 2
3 3
I need to filter this table using the following parameters:
house feature = 1
AND
house feature = 2
AND
house feature = 3
So that I get all houses with the requested feature.
I already tried to create something similar to this:
SELECT *
FROM houses
WHERE
house_feature = 1
AND
house_feature = 2
AND
house_feature = 3
But it doesn't work as I expected.
Is there a way to get this result with MySQL?
It seems that I acn filter the table using only the OR operator but this way I can't get the right result.
Thanks in advance for any help.
tony
You can do so ,by matching the distinct count of features per house ,so the house with exactly these 3 features will be returned
SELECT *
FROM t
WHERE
house_feature IN(1 ,2,3)
group by ID_house
having count(distinct house_feature) = 3
Demo
Supoose I have the following:
tbl_options
===========
id name
1 experience
2 languages
3 hourly_rate
tbl_option_attributes
=====================
id option_id name value
1 1 beginner 1
2 1 advanced 2
3 2 english 1
4 2 french 2
5 2 spanish 3
6 3 £10 p/h 10
7 3 £20 p/h 20
tbl_user_options
================
user_id option_id value
1 1 2
1 2 1
1 2 2
1 2 3
1 3 20
In the above example tbl_user_options stores option data for the user. We can store multiple entries for some options.
Now I wish to extend this, i.e. for "languages" I want the user to be able to specify their proficiency in a language (basic/intermediate/advanced). There will also be other fields that will have extended attributes.
So my question is, can these extended attributes be stored in the same table (tbl_user_options) or do I need to create more tables? Obviously if I put in a field "language_proficiency" it won't apply to the other fields. But this way I only have one user options table to manage. What do you think?
EDIT: This is what I propose
tbl_user_options
================
user_id option_id value lang_prof
1 1 2 null
1 2 1 2
1 2 2 3
1 2 3 3
1 3 20 null
My gut instinct would be to split the User/Language/Proficiency relationship out into its own tables. Even if you kept it in the same table with your other options, you'd need to write special code to handle the language case, so you might as well use a new table structure.
Unless your data model is in constant flux, I would rather have tbl_languages and tabl_user_languages tables to store those types of data:
tbl_languages
================
lang_id name
1 English
2 French
3 Spanish
tbl_user_languages
================
user_id lang_id proficiency hourly_rate
1 1 1 20
1 2 2 10
2 2 1 15
2 2 3 20
3 3 2 10
Designing a system that is "too generic" is a Turing tarpit trap for a relational SQL database. A document-based database is better suited to arbitrary key-value stores.
Excepting certain optimisations, your database model should match your domain model as closely as possible to minimise the object-relational impedance mismatch.
This design lets you display a sensible table of user language proficiencies and hourly rates with only two inner joins:
SELECT
ul.user_id,
u.name,
l.name,
ul.proficiency,
ul.hourly_rate
FROM tbl_user_languages ul
INNER JOIN tbl_languages l
ON l.lang_id = ul.lang_id
INNER JOIN tbl_users u
ON u.user_id = ul.user_id
ORDER BY
l.name, u.hour
Optionally you can split out a list of language proficiencies into a tbl_profiencies table, where 1 == Beginner, 2 == Advanced, 3 == Expert and join it onto tbl_user_languages.
i'm thinking it's a mistake to put "languages" as an option. while reading your text it seems to me that english is an option, and it might have an attribute from option_attributes.