I need help with a Query, i have a table like this:
| ID | codehwos |
| --- | ----------- |
| 1 | 16,17,15,26 |
| 2 | 15,32,12,23 |
| 3 | 53,15,21,26 |
I need an outpout like this:
| codehwos | number_of_this_code |
| -------- | ---------------------- |
| 15 | 3 |
| 17 | 1 |
| 26 | 2 |
I want to sum all the time a code is used in a row.
Can anyone make a query for doing it for all the code in one time?
Thanks
You have a very poor data format. You should not store lists in strings and never store lists of numbers in strings. SQL has a great data structure for storing lists. Hint: it is called a "table" not a "string".
That said, sometimes one is stuck with other people's really poor design choices. We wouldn't make them ourselves, but we still need to get something done. Assuming you have a list of codes, you can do what you want with:
select c.code, count(*)
from codes c join
table t
on find_in_set(c.code, t.codehwos) > 0
group by c.code;
If you have any influence over the data structure, then advocate for a junction table, the right way to store this data in a relational database.
Related
I have a database in mysql which has three rows, these rows has concatenated multiples values(values separated by a comma) already in it. I want to strike the rank using find_in_set function or any better function to get the positions.
Table
id | NUMBERS |
1 | 30,40,10 |
2 | 58,29,21 |
3 | 18,25,51 |
I want to rank each row in this format
id | NUMBERS | POSITION |
1 | 30,40,10 | 2,1,3 |
2 | 58,29,21 | 1,2,3 |
3 | 18,25,51 | 3,2,1 |
I Know the data representation and structure is wrong, but the data i have currently is made like the above and has a lot of data in it, meaning changing the structure would take me a lot of time, although I would change it later.
I need a workaround idea as to how to do this. I would be grateful for your support thanks.
Edit for future viewers: Aside from the accepted answer which helped me I found some really good info here .
I've got a database with a single table for displaying inventory on a website (RVs). It stores the typical info: year, make, model, etc. I originally made it with 6 extra columns for storing "special features", but I don't like having such a hard limit on what options can be listed. Since I've never messed with more than a single table my gut instinct was to just add 24 or so more columns to cover everything, but something in my head told me that there might be a better way. So when do I decide N columns is too many? The data in these columns will commonly not be unique.
(Sorry for crappy diagram)
Current table design:
-----------------------------------------------------------------------
| id | year | make | model | price | ft_1 | ft_2 | ft_3 | ft_4 | ft_5 |
-----------------------------------------------------------------------
| | | | | | | | | | |
-----------------------------------------------------------------------
Possible better design:
table #1
------------------------------------
| id | year | make | model | price |
------------------------------------
| | | | | |
------------------------------------
table #2
---------------------------------------------
| unique_id(?) | feature | unit_ref |
---------------------------------------------
| 0 | "Diesel Pusher" | 2,6,14 |
---------------------------------------------
I feel like a bonus of the second table might be that I could more easily propagate a dropdown containing all the previously entered features to speed up adding new units to inventory.
Is this the right way to go about it, or should I just add more columns and be content?
Thanks.
Believe it or not, your best option would likely be to add a third table.
Since each record in your rvs table can be linked to multiple rows in the features table, and each feature can correspond to multiple rvs, you have a many-to-many relationship which is inherently difficult to maintain in a relational dbms. By adding a third "intersection" table you convert it to a one-to-many-to-one relationship which can be enforced declaratively by the dbms.
Your table structure would then become something like
rvs
------------------------------------
| id | year | make | model | price |
------------------------------------
| | | | | |
------------------------------------
features
--------------------------
| id | feature |
--------------------------
| 1192 | "Diesel Pusher" |
--------------------------
rv_features
----------------------
| rv_id | feature_id |
----------------------
| | |
----------------------
How do you make use of this? Suppose you want to record the fact that the 2016 Travelmore CampMaster has a 25kW diesel generator. You would first add a record to rvs like
--------------------------------------------------
| id | year | make | model | price |
--------------------------------------------------
| 0231 | 2016 | Travelmore | CampMaster | 750000 |
| 2101 | 2016 | Travelmore | Domestant | 650000 |
--------------------------------------------------
(Note the value in the id column is entirely arbitrary; its sole purpose is to serve as the primary key which uniquely identifies the record. It can encode meaningful information, but it must be something that will not change throughout the life of the record it identifies.)
You then add (or already have) the generator in the features table:
--------------------------------
| id | feature |
--------------------------------
| 1192 | Diesel Pusher 450hp |
| 3209 | diesel generator 25kW |
--------------------------------
Finally, you associate the rv to the feature with a record in rv_features:
----------------------
| rv_id | feature_id |
----------------------
| 0231 | 3209 |
| 0231 | 1192 |
| 2101 | 3209 |
----------------------
(I've added a few other records to each table for context.)
Now, to retrieve the features of the 2016 CampMaster, you use the following SQL query:
SELECT r.year, r.make, r.model, f.feature
FROM rvs r, features f, rv_features rf
WHERE r.id = rf.rv_id
AND rv.feature_id = f.id
AND r.id = '2031';
to get
----------------------------------------------------------
| year | make | model | feature |
----------------------------------------------------------
| 2016 | Travelmore | CampMaster | diesel generator 25kW |
| 2016 | Travelmore | CampMaster | Diesel Pusher 450hp |
----------------------------------------------------------
To see the rvs with a 25kW generator, change the query to
SELECT r.year, r.make, r.model, f.feature
FROM rvs r, features f, rv_features rf
WHERE r.id = rf.rv_id
AND rv.feature_id = f.id
AND f.id = '3209';
Sherantha's link to A Quick-Start Tutorial on Relational Database Design actually looks like a good intro to table design and normalization; you might find it useful.
There is a thing calles "third normal form" it says that everything without the unique ids shuld be unique. This means you need to make a table for year, a table for make a table for models etc and a table where you can combine all these ids to one connected dataset.
But this is not always practical, io think the best way to take this is something in between, like tables for entrys that repeat very often, but there dont need to be an extra table for price with unique ids, that would be overkill i think.
Based upon your scenario, if you believe no. of features columns remain same then no need for second table. And in case if there any possibility that features can be increased at any time in future then you should break up your table into two. (RVS & Features). Then create a third table that identify RVS & features as it seems there is many-to-many relationship. So I suggest you to use three tables.
I think it is better for you to be more familiar with relational database design. This is a short but great article I have found earlier.
By referring table in the link, I have table category and another table name "package" to store category id.
http://ftp.nchu.edu.tw/MySQL/tech-resources/articles/hierarchical-data.html
Category
+-------------+----------------------+--------+
| category_id | name | parent |
+-------------+----------------------+--------+
| 1 | ELECTRONICS | NULL |
| 2 | TELEVISIONS | 1 |
| 3 | TUBE | 2 |
| 4 | LCD | 2 |
| 5 | PLASMA | 2 |
| 6 | PORTABLE ELECTRONICS | 1 |
| 7 | MP3 PLAYERS | 6 |
| 8 | FLASH | 7 |
| 9 | CD PLAYERS | 6 |
| 10 | 2 WAY RADIOS | 6 |
+-------------+----------------------+--------+
Is there anyway I can left join until there is no parent left without knowing how many times I have to join?
And second question, my table "package" is only storing the last/smallest category id, for example in the table is "7 - FLASH", is that a good practices to only store the last/smallest category id and refer it back by joining the table? Will this action making the database heavy by query it back every time?
Thanks in advance!
It is not possible to do such queries in MySQL.
If you need to keep this database structure, then the fastest approach is likely to select the relevant data from the table and then process the data client-side into the approach array/join.
The above may not work well if you cannot sufficiently narrow down the number of rows to SELECT out, in which case, recursively running multiple queries may be faster. On your second query, the best approach is to do something like WHERE id IN (list_of_parent_values) rather than 1 query per parent.
Lastly if you can change your data structure, there is a way of using special tree column values to efficiently select all of the nodes out with a single SQL query. Some more work is required to insert and re-organise the tree however.
There are a number of slightly differing implementations of this, see here for one such discussion:
http://web.archive.org/web/20110606032941/http://dev.mysql.com/tech-resources/articles/hierarchical-data.html
awesome_nested_set is also a ruby implementation of this pattern:
https://github.com/collectiveidea/awesome_nested_set
I have a comma delimited list like this saved in a mysql table:
-----------------
|id | list |
-----------------
| 4 |12,45,65,4 |
Each number in "list" corresponds with an ID in another table.
Is there a way so I can query the other table based on theses IDs and bring up those rows associated with the numbers in "list"?
Not any efficient way with your current schema. The correct and most efficient way to do it is to change the schema to hold multiple rows like this:
-----------------
|id | list |
-----------------
| 4 | 12 |
| 4 | 45 |
| 4 | 65 |
| 4 | 4 |
Then you use JOIN operations to connect 4 to every related row in your other table.
This is called database normalization and is a very important topic in database design. Relational database systems are built to handle just this types of problems in an efficient manner.
Imagine the following (very bad) table design in MSSQL2008R2:
Table "Posts":
| Id (PK, int) | DatasourceId (PK, int) | QuotedPostIds (nvarchar(255)) | [...]
| 1 | 1 | | [...]
| 2 | 1 | 1 | [...]
| 2 | 2 | 1 | [...]
[...]
| 102322 | 2 | 123;45345;4356;76757 | [...]
So, the column QuotedPostIds contains a semicolon-separated list of self-referencing PostIds (Kids, don't do that at home!). Since this design is ugly as a hell, I'd like to extract the values from the QuotedPostIds table to a new n:m relationship table like this:
Desired new table "QuotedPosts":
| QuotingPostId (int) | QuotedPostId (int) | DatasourceId (int) |
| 2 | 1 | 1 |
| 2 | 1 | 2 |
[...]
| 102322 | 123 | 2 |
| 102322 | 45345 | 2 |
| 102322 | 4356 | 2 |
| 102322 | 76757 | 2 |
The primary key for this table could either be a combination of QuotingPostId, QuotedPostId and DatasourceID or an additional artificial key generated by the database.
It is worth noticing that the current Posts table contains about 6,300,000 rows but only about 285,000 of those have a value set in the QuotedPostIds column. Therefore, it might be a good idea to pre-filter those rows. In any case, I'd like to perform the normalization using internal MSSQL functionality only, if possible.
I already read other posts regarding this topic which mostly dealt with split functions but neither could I find out how exactly to create the new table and also copying the appropriate value from the Datasource column, nor how to filter the rows to touch accordingly.
Thank you!
€dit: I thought it through and finally solved the problem using an external C# program instead of internal MSSQL functionality. Since it seems that it could have been done using Mikael Eriksson's suggestion, I will mark his post as an answer.
From comments you say you have a string split function that you you don't know how to use with a table.
The answer is to use cross apply something like this.
select P.Id,
S.Value
from Posts as P
cross apply dbo.Split(';', P.QuotedPostIds) as S