I am working on a rewrite for a registration app and starting to think about how I want to design the DB structure. I need the app to be flexible because some events offer different things. Here's a particular one:
Each event offers shirts, but not every event offers the same sizes. I figured I'd have a Shirt_Size table with all possible options and then in a form to create a new Event, they'd be able to just checkbox what shirts they want. Where would I store the particular subset of sizes for that particular event? I will need to query that to populate a drop down for the form that will be for registering for events.
I figured I could do some kind of comma-separated column for the Event model that is different value IDs from Shirt_Sizes? But I've been reading that it's bad to do that, so I'm not sure how this is normally handled. Thanks!
You can create a third table that has a column for event_id and shirt_size_id and populate it as necessary. Say event1 only has small and medium shirts, you would add two rows to the table.
id event_id shirt_size_id
1 1 1
2 1 2
And if the 2nd event had small medium and large shirts, add 3 rows to the new table.
id event_id shirt_size_id
3 2 1
4 2 2
5 2 3
Then when you query for data to populate the drop down, you can join all three tables.
Related
I am trying to create a query in Access that picks out rows in a table based on the existence of values in another table. I am looking at a table that contains the state of different ID numbers and checking that for whatever state that ID is at it has progressed through the lower states.
For example, Each ID goes from apprentice to journeyman to master. If an ID is at master, as noted in the State table, there should be a record in the Events table for that ID being at apprentice and master as well.
The query should return the IDs from the State table that are at the Master state but have not properly progressed through the states based on the entries in the Events table.
With the two tables below, the query should return IDs 2. ID 2 is listed at Master but never was at the Journeyman state.
State Table:
ID Status
1 Master
2 Master
3 Apprentice
4 Journeyman
Events Table:
Date Status ID
7/25/17 Master 1
7/25/17 Master 2
7/24/17 Journeyman 1
7/24/17 Journeyman 3
7/20/17 Apprentice 4
7/20/17 Apprentice 3
7/20/17 Apprentice 2
7/20/17 Apprentice 1
I have created a query to look for IDs marked as Master. But I'm not sure where to go from there to look at the Events table for IDs marked as Master in the State table.
This is my simple query. This is my first time really using Access, any pointers would be appreciated!
If no Journeyman is the only event criteria then consider:
SELECT * FROM State WHERE Status="Master" AND NOT ID IN (SELECT ID FROM Events WHERE Status="Journeyman");
Date is a reserved word. Should not use reserved words as names. Better would be EventDate.
I have two tables, one user table and an items table. In the user table, there is the field "items". The "items" table only consists of a unique id and an item_name.
Now each user can have multiple items. I wanted to avoid creating a third table that would connect the items with the user but rather have a field in the user_table that stores the item ids connected to the user in a "csv" field.
So any given user would have a field "items" that could have a value like "32,3,98,56".
It maybe is worth mentioning that the maximum number of items per user is rather limited (<5).
The question: Is this approach generally a bad idea compared to having a third table that contains user->item pairs?
Wouldn't a third table create quite an overhead when you want to find all items of a user (I would have to iterate through all elements returned by MySQL individually).
You don't want to store the value in the comma separated form.
Consider the case when you decide to join this column with some other table.
Consider you have,
x items
1 1, 2, 3
1 1, 4
2 1
and you want to find distinct values for each x i.e.:
x items
1 1, 2, 3, 4
2 1
or may be want to check if it has 3 in it
or may be want to convert them into separate rows:
x items
1 1
1 2
1 3
1 1
1 4
2 1
It will be a HUGE PAIN.
Use atleast normalization 1st principle - have separate row for each value.
Now, say originally you had this as you table:
x item
1 1
1 2
1 3
1 1
1 4
2 1
You can easily convert it into csv values:
select x, group_concat(item order by item) items
from t
group by x
If you want to search if x = 1 has item 3. Easy.
select * from t where x = 1 and item = 3
which in earlier case would use horrible find_in_set:
select * from t where x = 1 and find_in_set(3, items);
If you think you can use like with CSV values to search, then first like %x% can't use indexes. Second, it will produce wrong results.
Say you want check if item ab is present and you do %ab% it will return rows with abc abcd abcde .... .
If you have many users and items, then I'd suggest create separate table users with an PK userid, another items with PK itemid and lastly a mapping table user_item having userid, itemid columns.
If you know you'll just need to store and retrieve these values and not do any operation on it such as join, search, distinct, conversion to separate rows etc. etc. - may be just may be, you can (I still wouldn't).
Storing complex data directly in a relational database is a nonstandard use of a relational database. Normally they are designed for normalized data.
There are extensions which vary according to the brand of software which may help. Or you can normalize your CSV file into properly designed table(s). It depends on lots of things. Talk to your enterprise data architect in this case.
Whether it's a bad idea depends on your business needs. I can't assess your business needs from way out here on the internet. Talk to your product manager in this case.
I'm designing a web app which allows users to attend events and search for specific types of events.
Say, for instance, that these events are taking place in Hogwarts. The students have their own table where their studentID is held as a primary key, and this also contains which house they are a part of (of which there are 4), the subject they take, and which year of study they are in (e.g. 1 or 4 or 5, etc). The events can be for all students, specifically for 4th year students in the Ravenclaw house, or anywhere in between.
The events are held in an events table, which contains an eventID as the primary key, but I'm not sure how to hold the data for the house/year/subject it is aimed at. Obviously if an event were only aimed at 3rd year Hufflepuffs who take Potions, or something similarly specific, I could hold it within the same table. However, what if the event is for any year of Hufflepuffs (and not any Slytherins, etc)? Or if all students from all years, houses and subjects are eligible to attend? Will I need a table which holds all the years for each event and a separate table for which houses it's for and a further separate table for the subject it's aimed at?
Any advice or links are appreciated.
I think there are two ways but you definitely need at least one more table for the associations. Either you want to be very specific, about the combinations possible or you want to do it generally, like: only third years, only hufflepuffs, then the combination of the two values will be only third year hufflepuffs.
What I am trying to say are these two options.
1) One table that holds rows with very specific details:Event ID and the explicit combinations of all possible options (Here you will have a lot of rows)
This would mean that the event can be associated with second and third year hufflepuffs, but only second year slytherins.
association_id event_id year_id house_id subject_id
1 1 second hufflepuff potions
2 1 third hufflepuff potions
3 1 second slytherin potions
2) One table per property (here the disctinction is not as clear but you only have to create one row per property etc.
The following two tables could be used to store that all hufflepuffs and all slytherins that are in second or third year might attend
association_id event_id year_id
1 1 second
2 1 third
association_id event_id house_id
1 1 hufflepuff
2 1 slytherin
Does that answer your question or at least help you to find a solution?
Mybe if you can describe the target you are aiming at more closely one can find a solution suitable for your Problem together.
EDIT
People think this question is too broad so I'm narrowing things down a bit here:
I have a table with dual primary keys: roomID and userID.
Here is some example data:
roomID | userID
1 | 5
1 | 9
1 | 10
1 | 12
2 | 5
2 | 9
2 | 10
3 | 5
3 | 17
Given a list of users: 5,9,10, how can I return the roomID containing ONLY those users? So in this case it should return 2.
I hope this can be done within 1 SQL query.
Any help would be appreicated.
ORIGINAL QUESTION
I am making a chat room application and need to design a database backend for it. All the rooms are created on the fly and are destroyed when the last user exits the room. Users are able to add other users to any room they are in.
Currently this is my design:
I have a chatroom table with two columns. The two columns are both primary keys for the table (so a row is considered duplicate only when both columns are the same). The first column is the room ID. The second column is a user ID. The idea I have here is with the same room ID, there can be many users in this room (so rows with same room ID but different user ID). When I need to create a new room, I simply select MAX(room ID) + 1 and create a new room with this ID and add the users into it.
Given a list of users IDs (such as 1,5,31,12), I need to find out if a room is already created for them. In other words, I need to determine if there are rows all with the same room ID having users IDs 1,5,31,12. However, if a room is created with users 1,5,31,12,6 (one or more extra users), this should not count as room already created. I will then need to create a new room for them and add the users to that. Same goes for less users than the list.
Right now I'm having trouble forming the query to determine if I need to create a new room or not, and if not, retrieve the room ID of the existing room.
Any help would be appreciated.
Also, I think this design is quite cumbersome, you are welcome to suggest a better database design.
P.S. the database I'm using is MySQL
I think yoy can add 1 more col to the chatroom table, name num_member, this is number of member in room( or better have room(room_id, number_member) table). To make it simple first, I assume you have num_member in chatroom. This query might work:
Select * From chatroom where user_id IN ($userIdList) Group by room_id HAVING count(*) = chatroom.num_member
Hope this help
Hey. I have 160 columns that are filled with data when a user fills a report form out and submit it. A few of these sets of columns contain similar data, but there needs to be multiple instance of this data per record set as it may be different per instance in the report.
For example, an employee opens a case by a certain type at one point in the day, then at another point in the day they open another case of a different type. I want to create totals per user based on the values in these columns. There is one column set that I want to target right now, case type. I would like to be able to see all instances of the value "TSTO" in columns CT1, CT2, CT3... through CT20. Then have that sorted by the employee ID number, which is just one column in the table.
Any ideas? I am struggling with this one.
So far I have SELECT CT1, CT2, CT3, CT4, CT5, CT6, CT7, CT8, CT9, CT10, CT11, CT12, CT13, CT14, CT15, CT16, CT17, CT18, CT19, CT20 FROM REPORTS GROUP BY OFFICER
This will display the values of all the case type entries in a record set but I need to count them, I tried to use,
SELECT CT1, CT2, CT3, CT4, CT5, CT6, CT7, CT8, CT9, CT10, CT11, CT12, CT13, CT14, CT15, CT16, CT17, CT18, CT19, CT20 FROM REPORTS COUNT(TSTO) GROUP BY OFFICER
but it just spits an error. I am fairly new to mysql databasing and php, I feel I have a good grasp but query'ing the database and the syntax involved is a tad bit confused and/or overwhelming right now. Just gotta learn the language. I will keep looking and I have found some similar things on here but I don't understand what I am looking at (completely) and I would like to shy away from using code that "works" but I don't understand fully.
Thank you very much :)
Edit -
So this database is an activity report server for the days work for the employees. The person will often open cases during the day. These cases vary in type, and their different types are designated by a four letter convention. So your different case types could be TSTO, DOME, ASBA, etc etc. So the user will fill out their form throughout the day then submit it down to the database. That's all fine :) Now I am trying to build a page which will query the database by user request for statistics of a user's activities. So right now I am trying to generate statistics. Specifically, I want to be able to generate the statistic of, and in human terms, "HOW MANY OCCURENCES OF "USER INPUTTED CASE TYPE" ARE THERE FOR EMPLOYEEIDXXX"
So when a user submits a form they will type in this four letter case type up to 20 times in one form, there is 20 fields for this case type entry, thus there is 20 columns. So these 20 columns for case type will be in one record set, one record set is generated per report. Another column that is generated is the employeeid column, which basically identifies who generated the record set through their form.
So I would like to be able to query all 20 columns of case type, across all record sets, for a defined type of case (TSTO, DOME, ASBA, etc etc) and then group that to corresponding user(s).
So the output would look something like,
316 TSTO's for employeeid108
I hope this helps to clear it up a bit. Again I am fairly fresh to all of this so I am not the best with the vernacular and best practices etc etc...
Thanks so much :)
Edit 2 -
So to further elaborate on what I have going on, I have an HTML form that has 164 fields. Each of these fields ultimately puts a value into a column in a single record set in my DB, each submission. I couldn't post images or more than two URLs so I will try to explain it the best I can without screenshots.
So what happens is this information gets in the DB. Then there is the query'ing. I have a search page which uses an HTML form to select the type of information to be searched for. It then displays a synopsis of each report that matches the query. The user than enters the REPORT ID # for the report they want to view in full into another small form (an input field with a submit button) which brings them to a page with the full report displayed when they click submit.
So right now I am trying to do totals and realizing my DB will be needing some work and tweaking to make it easier to create querys for it for different information needed. I've gleaned some good information so far and will continue to try and provide concise information about my setup as best I can.
Thanks.
Edit 3 -
Maybe you can go to my photobucket and check them out, should let me do one link, there is five screenshots, you can kind of see better what I have happening there.
http://s1082.photobucket.com/albums/j376/hughessa
:)
The query you are looking for would be very long and complicated for your current db schema.
Every table like (some_id, column1, column2, column3, column4... ) where columns store the same type of data can be also represented by a table (some_id, column_number, column_value ) where instead of 1 row with values for 20 columns you have 20 rows.
So your table should rather look like:
officer ct_number ct_value
1 CT1 TSTO
1 CT2 DOME
1 CT3 TSTO
1 CT4 ASBA
(...)
2 CT1 DOME
2 CT2 TSTO
For a table like this if you wanted to find how many occurences of different ct_values are there for officer 1 you would use a simple query:
SELECT officer, ct_value, count(ct_value) AS ct_count
FROM reports WHERE officer=1 GROUP BY ct_value
giving results
officer ct_value ct_count
1 TSTO 2
1 DOME 1
1 ASBA 1
If you wanted to find out how many TSTO's are there for different officers you would use:
SELECT officer, ct_value, count( officer ) as ct_count FROM reports
WHERE ct_value='TSTO' GROUP BY officer
giving results
officer ct_value ct_count
1 TSTO 2
2 TSTO 1
Also any type of query for your old schema can be easily converted to new schema.
However if you need store additional information about every particular report I suggest having two tables:
Submissions
submission_id report_id ct_number ct_value
primary key
auto-increment
------------------------------------------------
1 1 CT1 TSTO
2 1 CT2 DOME
3 1 CT3 TSTO
4 1 CT4 ASBA
5 2 CT1 DOME
6 2 CT2 TSTO
with report_id pointing to a record in another table with as many columns as you need for additional data:
Reports
report_id officer date some_other_data
primary key
auto-increment
--------------------------------------------------------------------
1 1 2011-04-29 11:28:15 Everything went ok
2 2 2011-04-29 14:01:00 There were troubles
Example:
How many TSTO's are there for different officers:
SELECT r.officer, s.ct_value, count( officer ) as ct_count
FROM submissions s JOIN reports r ON s.report_id = r.report_id
WHERE s.ct_value='TSTO'
GROUP BY r.officer