i wanna create a 2 level status message system. Which is the best way to create a tables ?
Scope:
User sets a Status Message
Users Reply to the status message
this is a picture showing it
Tables i have created
users (id, name .... )
status_messages (id, message, time, user_id)
status_message_replies (id, message, time, status_message_id, user_d)
Some one suggested this can be done in a single table format
status_messages (id, pid, message, time, user_id)
where pid = selfId or ParentId of the status.
I wanna know which is the best method to create the system ?
As long as the original messages and the responses have the same structure (set of attributes, or columns) then you can use the single table approach. It has the advantage that you can search over original messages and responses with a single query.
The set of original messages can be found where pid = selfid and the responses where pid <> selfid. If it's important to be able to see the original and response messages separately (without knowledge of the storage mechanism) you can encapsulate the above conditions in two VIEWs: OriginalMessages and Responses.
If the originals and responses have different attributes (for instance, if you want the original to allow links to URLs, photos, etc) you might consider using two separate tables. But even there, I'd probably argue for the one table structure with a separate, extender table for the additional attributes. That means you don't have to store often-empty columns for those original messages that don't use the extended attributes, and you can later easily add the extended attributes to the response messages as well (if desired).
A classical IS-A relationship: every reply is a message with an extra attribute (the message it is a reply to).
This is probably not the best way to model it. You'll be running the risk of having to write a lot of UNION queries over those two tables.
Alternatives:
just one table: status_messages (id, message, time, status_message_id, user_id), and allowing status_message_id to be NULL
use a HAS-A: one table status_messages (id, message, time, user_id) and one table replies (reply_id, replies_to_id
The former has the disadvantage that working with NULL is tricky in SQL.
The latter will necessitate joins when you want to query replies specifically.
BTW it's much clearer (IMO) to name columns after the relationship they stand for, not the table they refer to.
Related
I saw many threads asking about keeping history of records in mysql. However, I'm not quite sure they are suitable with my case.
I'm developing an application form with a lot of user information. So far, I have to normalize it into 12 tables even though most of them have 1:1 relations but I though they would be good in the future use:
User (Id, Fullname, Username, Email, CreatedDate, UpdatedDate, ...)
Family (Id, UserId, Name, Relation, Job, ...)
Address (Id, UserId, Road, District, Province, ...)
...
When clients filled all the fields in the form, they have two options, firstly, they can save it as draft, secondly, they can confirm sending the application and can't change it anymore.
I have done some research so far. They are many ways to do it. For example, I could duplicate all the tables with some additional fields; VersionId. However due to the enormous number of tables, I don't think it's a good idea.
So, what I think is to add VersionId to each existing tables. When they save the form as draft, I would just put the information without touching the VersionId field, however, I would increase VersionId by 1 whenever the user confirm submitting the application.
Any suggestion would be really welcomed.
Add a status column to each table. It can have the values draft, current, and history.
When the user makes a change to their data, create a new row with status = draft. As they edit, you modify that row. When they confirm the changes, you set the old current row's status to history, and set the draft row's status to current.
I think it mainly depends on the business requirement (since it doesn't sound like there would be so many updates for the same user I am assuming that performance is not a concern but you may want to think about that too since an insert in this case is cheaper than an update).
So the question you need to ask yourself is does the business require that you keep the history or not? for example if user A fills out the form, and later on he updates some of the information e.g. he has a new address, do you want to be able to know what were his previous addresses or not? If you do then you have to store them (I would add the date of the change in addition to the version id)
I hope someone can help me with this:
I have a simple query combining a list of names and basic details with another table containing more specific information. Some names will necessarily appear more than once and arbitrary distinctions like "John Smith 1" and "John Smith 2" are not an option, so I have been using an autonumber to keep the records distinct.
The problem is that my query is creating two records for each name that appears more than once. For example, there are two clients named 'Sophoan', each with a different id number, and the query has picked up each one twice resulting in four records (in total there are 122 records when there should only be 102). 'Unique values' is set to 'yes'.
I've researched as much as I can and am completely stuck. I've tried to tinker with sql but it always comes back with errors, I presume because there are too many fields in the query.
What am I missing? Or is a query the wrong approach and I need to find another way to combine my tables?
Project in detail: I'm building a database for a charity which has two main activities: social work and training. The database is to record their client information and the results of their interactions with clients (issues they asked for help with, results of training workshops etc.). Some clients will cross over between activities which the organisation wants to track, hence all registered clients go into one list and individual tables spin of that to collect data for each specific activity the client takes part in. This query is supposed to be my solution for combining these tables for data entry by the user.
At present I have the following tables:
AllList (master list of client names and basic contact info; 'Social Work Register' and 'Participant Register' join to this table by
'Name')
Social Work Register (list of social work clients with full details
of each case)
Social Work Follow-up Table (used when staff call social work clients
to see how their issue is progressing; the register has too many
columns to hold this as well; joined to Register by 'Client Name')
Participants Register (list of clients for training and details of
which workshops they were attended and why they were absent if they
missed a session)
Individual workshop tables x14 (each workshop includes a test and
these tables records the clients answers and their score for each
individual test; there will be more than 20 of these when the
database is finished; all joined to the 'Participants Register' by
'Participant Name')
Queries:
Participant Overview Query (links the attendance data from the 'Register' with the grading data from each Workshop to present a read-only
overview; this one seems to work perfectly)
Social Work Query (non-functional; intended to link the 'Client
Register' to the 'AllList' for data entry so that when a new client
is registered it creates a new record in both tables, with the
records matched together)
Participant Query (not yet attempted; as above, intended to link the
'Participant Register' to the 'AllList' for data entry)
BUT I realised that queries can't be used for data entry, so this approach seems to be a dead end. I have had some success with using subforms for data entry but I'm not sure if it's the best way.
So, what I'm basically hoping to achieve is a way to input the same data to two tables simultaneously (for new records) and have the resulting records matched together (for new entries to existing records). But it needs to be possible for the same name to appear more than once as a unique record (e.g. three individuals named John Smith).
[N.B. There are more tables that store secondary information but aren't relevant to the issue as they are not and will not be linked to any other tables.]
I realised that queries can't be used for data entry
Actually, non-complex queries are usually editable as long as the table whose data you want to edit remains 'at the core' of the query. Access applies a number of factors to determine if a query is editable or not.
Most of the time, it's fairly easy to figure out why a query has become non-editable.
Ask yourself the question: if I edit that data, how will Access ensure that exactly that data will be updated, without ambiguity?
If your tables have defined primary keys and these are part of your query, and if there are no grouping, calculated fields (fields that use some function to change or test the value of that field), or complex joins, then the query should remain editable.
You can read more about that here:
How to troubleshoot errors that may occur when you update data in Access queries and in Access forms
Dealing with Non-Updateable Microsoft Access Queries and the Use of Temporary Tables.
So, what I'm basically hoping to achieve is a way to input the same data to two tables simultaneously (for new records) and have the resulting records matched together (for new entries to existing records). But it needs to be possible for the same name to appear more than once as a unique record (e.g. three individuals named John Smith).
This remark actually proves that you have design issues in your database.
A basic tenet of Database Design is to remove redundancy as much as possible. One of the reasons is actually to avoid having to update the same data in multiple places.
Another remark: you are using the Client's name as a Natural Key. Frankly, it is not a very good idea. Generally, you want to make sure that what constitutes a Primary key for a table is reliably unique over time.
Using people's names is generally the wrong choice because:
people change name, for instance in many cultures, women change their family name after they get married.
There could also have been a typo when entering the name and now it can be hard to correct it if that data is used as a Foreign Key all in different tables.
as your database grows, you are likely to end up with some people having the same name, creating conflicts, or forcing the user to make changes to that name so it doesn't create a duplicate.
The best way to enforce uniqueness of records in a table is to use the default AutoNumber ID field proposed by Access when you create a new table. This is called a Surrogate key.
It's not mean to be edited, changed or even displayed to the user. It's sole purpose is to allow the primary key of a table to be unique and non-changing over time, so it can reliably be used as a way to reference a record from one table to another (if a table needs to refer to a particular record, it will contain a field that will hold that ID. That field is called a Foreign Key).
The names you have for your tables are not precise enough: think of each table as an Entity holding related data.
The fact that you have a table called AllList means that its purpose isn't that well-thought of; it sounds like a catch-all rather than a carefully crafted entity.
Instead, if this is your list of clients, then simply call it Client. Each record of that table holds the information for a single client (whether to use plural or singular is up to you, just stick to your choice though, being consistent is hugely important).
Instead of using the client's name as a key, create an ID field, an Autonumber, and set it as Primary Key.
Let's also rename the "Social Work Register", which holds the Client's cases, simply as ClientCase. That relationship seems clear from your description of the table but it's not clear in the table name itself (by the way, I know Access allows spaces in table and field names, but it's a really bad idea to use them if you care at least a little bit about the future of your work).
In that, create a ClientID Number field (a Foreign Key) that will hold the related Client's ID in the ClientCase table.
You don't talk about the relationship between a Client and its Cases. This is another area where you must be clear: how many cases can a single Client have?
At most 1 Case ? (0 or 1 Case)
exactly 1 Case?
at least one Case? (1 or more Cases)
any number of Cases? (0 or more Cases)
Knowing this is important for selecting the right type of JOIN in your queries. It's a crucial part of the design assumptions when building your database.
For instance, in the most general case, assuming that a Client can have 0 or more cases, you could have a report that displays the Client's Name and the number of cases related to them like this:
SELECT Client.Name,
Count(ClientCase.ID) AS CountOfCases
FROM Client
LEFT JOIN ClientCase
ON Client.ID = ClienCase.ClientID
GROUP BY Client.Name
You've described your basic design a bit more, but that's not enough. Show us the actual table structures and the SQL of the queries you tried. From the description you give, it's hard to really understand the actual details of the design and to tell you why it fails and how to make it work.
I am developing a forum in PHP MySQL. I want to make my forum as efficient as I can.
I have made these two tables
tbl_threads
tbl_comments
Now, the problems is that there is a like and dislike button under the each comment. I have to store the user_name which has clicked the Like or Dislike Button with the comment_id. I have made a column user_likes and a column user_dislikes in tbl_comments to store the comma separated user_names. But on this forum, I have read that this is not an efficient way. I have been advised to create a third table to store the Likes and Dislikes and to comply my database design with 1NF.
But the problem is, If I make a third table tbl_user_opinion and make two fields like this
1. comment_id
2. type (like or dislike)
So, will I have to run as many sql queries as there are comments on my page to get the like and dislike data for each comment. Will it not inefficient. I think there is some confusion on my part here. Can some one clarify this.
You have a Relational Scheme like this:
There are two ways to solve this. The first one, the "clean" one is to build your "like" table, and do "count(*)'s" on the appropriate column.
The second one would be to store in each comment a counter, indicating how many up's and down's have been there.
If you want to check, if a specific user has voted on the comment, you only have to check one entry, wich you can easily handle as own query and merge them two outside of your database (for this use a query resulting in comment_id and kind of the vote the user has done in a specific thread.)
Your approach with a comma-seperated-list is not quite performant, due you cannot parse it without higher intelligence, or a huge amount of parsing strings. If you have a database - use it!
("One Information - One Dataset"!)
The comma-separate list violates the principle of atomicity, and therefore the 1NF. You'll have hard time maintaining referential integrity and, for the most part, querying as well.
Here is one way to do it in a normalized fashion:
This is very clustering-friendly: it groups up-votes belonging to the same comment physically close together (ditto for down-votes), making the following query rather efficient:
SELECT
COMMENT.COMMENT_ID,
<other COMMENT fields>,
COUNT(DISTINCT UP_VOTE.USER_ID) - COUNT(DISTINCT DOWN_VOTE.USER_ID) SCORE
FROM COMMENT
LEFT JOIN UP_VOTE
ON COMMENT.COMMENT_ID = UP_VOTE.COMMENT_ID
LEFT JOIN DOWN_VOTE
ON COMMENT.COMMENT_ID = DOWN_VOTE.COMMENT_ID
WHERE
COMMENT.COMMENT_ID = <whatever>
GROUP BY
COMMENT.COMMENT_ID,
<other COMMENT fields>;
[SQL Fiddle]
Please measure on realistic amounts of data if that works fast enough for you. If not, then denormalize the model and cache the total score in the COMMENT table, and keep it current it through triggers every time a new row is inserted to or deleted from *_VOTE tables.
If you also need to get which comments a particular user voted on, you'll need indexes on *_VOTE {USER_ID, COMMENT_ID}, i.e. the reverse of the primary/clustering key above.1
1 This is one of the reasons why I didn't go with just one VOTE table containing an additional field that can be either 1 (for up-vote) or -1 (for down-vote): it's less efficient to cover with secondary indexes.
In Meetup.com, when you join a meetup group, you are usually required to complete a profile for that particular group. For example, if you join a movie meetup group, you may need to list the genres of movies you enjoy, etc.
I'm building a similar application, wherein users can join various groups and complete different profile details for each group. Assume the 2 possibilities:
Users can create their own groups and define what details to ask users that join that group (so, something a bit dynamic -- perhaps suggesting that at least an EAV design is required)
The developer decides now which groups to create and specify what details to ask users who join that group (meaning that the profile details will be predefined and "hard coded" into the system)
What's the best way to model such data?
More elaborate example:
The "Movie Goers" group request their members to specify the following:
Name
Birthdate (to be used to compute member's age)
Gender (must select from "male" or "female")
Favorite Genres (must select 1 or more from a list of specified genres)
The "Extreme Sports" group request their member to specify the following:
Name
Description of Activities Enjoyed (narrative form)
Postal Code
The bottom line is that each group may require different details from members joining their group. Ideally, I would like anyone to create a group (ala MeetUp.com). However, I also need the ability to query for members fairly well (e.g. find all women movie goers between the ages of 25 and 30).
For something like this....you'd want maximum normalization, so you wouldn't have duplicate data anywhere. Because your user-defined tables could possibly contain the same type of record, I think that you might have to go above 3NF for this.
My suggestion would be this - explode your tables so that you have something close to 6NF with EAV, so that each question that users must answer will have its own table. Then, your user-created tables will all reference one of your question tables. This avoids the duplication of data issue. (For instance, you don't want an entry in the "MovieGoers" group with the name "John Brown" and one in the "Extreme Sports" group with the name "Johnny B." for the same user; you also don't want his "what is your favorite color" answer to be "Blue" in one group and "Red" in another. Any data that can span across groups, like common questions, would be normalized in this form.)
The main drawback to this is that you'd end up with a lot of tables, and you'd probably want to create views for your statistical queries. However, in terms of pure data integrity, this would work well.
Note that you could probably get away with only factoring out the common fields, if you really wanted to. Examples of common fields would include Name, Location, Gender, and others; you could also do the same for common questions, like "what is your favorite color" or "do you have pets" or something to that extent. Group-specific questions that don't span across groups could be stored in a separate table for that group, un-exploded. I wouldn't advise this because it wouldn't be as flexible as the pure 6NF option and you run the risk of duplication (how do you predetermine which questions won't be common questions?) but if you really wanted to, you could do this.
There's a good question about 6NF here: Would like to Understand 6NF with an Example
I hope that made some sense and I hope it helps. If you have any questions, leave a comment.
Really, this is exactly a problem for which SQL is not a right solution. Forget normalization. This is exactly the job for NoSQL document stores. Every user as a document, having some essential fields like id, name, pwd etc. And every group adds possibility to add some fields. Unique fields can have names group-id-prefixed, shared fields (that grasp some more general concept) can have that field name free.
Except users (and groups) then you will have field descriptions with name, type, possible values, ... which is also very good for a document store.
If you use key-value document store from the beginning, you gain this freeform possibility of structuring your data plus querying them (though not by SQL, but by the means this or that NoSQL database provides).
First i'd like to note that the following structure is just a basis to your DB and you will need to expand/reduce it.
There are the following entities in DB:
user (just user)
group (any group)
template (list of requirement united into template to simplify assignment)
requirement (single requirement. For example: date of birth, gender, favorite sport)
"Modeling":
**User**
user_id
user_name
**Group**
name
group_id
user_group
user_id (FK)
group_id (FK)
**requirement**:
requirement_id
requirement_name
requirement_type (FK) (means the type: combo, free string, date) - should refers to dictionary)
**template**
template_id
template_name
**template_requirement**
r_id (FK)
t_id (FK)
The next step is to model appropriate schema for storing restrictions, i.e. validating rule for any requirement in any template. We have to separate it because for different groups the same restrictions can be different (for example: "age"). You can use the following table:
**restrictions**
group_id
template_id
requirement_id (should be here as template_id because the same requirement can exists in different templates and any group can consists of many templates)
restriction_type (FK) (points to another dict: value, length, regexp, at_least_one_value_choosed and so on)
So, as i said it is the basis. You can feel free to simplify this schema (wipe out tables, multiple templates for group). Or you can make it more general adding opportunity to create and publish temaplate, requirements and so on.
Hope you find this idea useful
You could save such data as JSON or XML (Structure, Data)
User Table
Userid
Username
Password
Groups -> JSON Array of all Groups
GroupStructure Table
Groupid
Groupname
Groupstructure -> JSON Structure (with specified Fields)
GroupData Table
Userid
Groupid
Groupdata -> JSON Data
I think this covers most of your constraints:
users
user_id, user_name, password, birth_date, gender
1, Robert Jones, *****, 2011-11-11, M
group
group_id, group_name
1, Movie Goers
2, Extreme Sports
group_membership
user_id, group_id
1, 1
1, 2
group_data
group_data_id, group_id, group_data_name
1, 1, Favorite Genres
2, 2, Favorite Activities
group_data_value
id, group_data_id, group_data_value
1,1,Comedy
2,1,Sci-Fi
3,1,Documentaries
4,2,Extreme Cage Fighting
5,2,Naked Extreme Bike Riding
user_group_data
user_id, group_id, group_data_id, group_data_value_id
1,1,1,1
1,1,1,2
1,2,2,4
1,2,2,5
I've had similar issues to this. I'm not sure if this would be the best recommendation for your specific situation but consider this.
Provide a means of storing data as XML, or JSON, or some other format that delimits the data, but basically stores it in field that has no specific format.
Provide a way to store the definition of that data
Provide a lookup/index table for the data.
This is a combination of techniques indicated already.
Essentially, you would create some interface to your clients to create a "form" for what they want saved. This form would indicated what pieces of information they want from the user. It would also indicate what pieces of information you want to search on.
Save this information to the definition table.
The definition table is then used to describe the user interface for entering data.
Once user data is entered, save the data (as xml or whatever) to one table with a unique id. At the same time, another table will be populated as an index with
id where the xml data was saved
name of field data is stored in
value of field data stored.
id of data definition.
now when a search commences, there should be no issue in searching for the information in the index table by name, value and definition id and getting back the id of the xml/json (or whatever) data you stored in the table that the data form was stored.
That data should be transformable once it is retrieved.
I was seriously sketchy on the details here, I hope this is enough of an answer to get you started. If you would like any explanation or additional details, let me know and I'll be happy to help.
if you're not stuck to mysql, i suggest you to use postgresql which provides build-in array datatypes.
you can define a define an array of varchar field to store group specific fields, in your groups table. to store values you can do the same in the membership table.
comparing to string parsing based xml types, this array approach will be really fast.
if you dont like array approach you can check out xml datatypes and an optional hstore datatype which is a key-value store.
I am developing a database to store test data. Each piece of data has 11 tags of metadata. Currently I have a separate table for each of the metadata options. I have seen a few questions on here regarding best practices for numerous small tables, but I thought I'd pose the question for my own project because I didn't get a clear answer from the other questions asked.
Here is my table list, with the fields in each table:
Source Type - id, name, description
For Flight - id, name, description
Site - id, name, abrv, description
Stand - id, site (FK site table), name, abrv, descrition
Sensor Type - id, name, channels, descrition
Vehicle - id, name, abrv, descrition
Zone - id, vehicle (FK vehicle table), name, abrv, description
Event Type - id, name, description
Event - id, event type (FK to event type Table), name, descrition
Analysis - id, name, descrition
Bandwidth - id, name, descrition
You can see the fields are more or less the same in each of these tables. There are three tables that reference another table.
Would it be better to have just one large table called something like Meta with the following fields:
Meta: id, metavalue, name, abrv, FK, value, descrition
where metavalue = one of the above table names
and FK = a reference to another row in the Meta table in place of a foreign key?
I am new to databases and multiple tables seems most intuitive, but one table makes the programming easier.
So questions are:
Is it good practice to reduce the number of tables and put all static values in one table.
Is it bad to have a self referencing table.
FYI I am making this web database using django and mysql on a windows server with NTFS formatting.
Tips and best practices appreciate.
thanks.
"Would it be better to have just one large table" - emphatically and categorically, NO!
This anti-pattern is sometimes referred to as 'The one table to rule them all"!
Ten Common Database Design Mistakes: One table to hold all domain values.
Using the data in a query is much easier
Data can be validated using foreign key constraints very naturally,
something not feasible for the other
solution unless you implement ranges
of keys for every table – a terrible
mess to maintain.
If it turns out that you need to keep more information about a
ShipViaCarrier than just the code,
'UPS', and description, 'United Parcel
Service', then it is as simple as
adding a column or two. You could even
expand the table to be a full blown
representation of the businesses that
are carriers for the item.
All of the smaller domain tables will fit on a single page of disk.
This ensures a single read (and likely
a single page in cache). If the other
case, you might have your domain table
spread across many pages, unless you
cluster on the referring table name,
which then could cause it to be more
costly to use a non-clustered index if
you have many values.
You can still have one editor for all rows, as most domain tables will
likely have the same base
structure/usage. And while you would
lose the ability to query all domain
values in one query easily, why would
you want to? (A union query could
easily be created of the tables easily
if needed, but this would seem an
unlikely need.)
Most of these look like they won't do anything but expand codes into descriptions. Do you even need the tables? Just define a bunch of constants, or codes, and then have a dictionary of long descriptions for the codes.
The field in the referring table just stores the code. eg: "SRC_FOO", "EVT_BANG" etc.
This is also often known as the One True Lookup Table (OTLT) - see my old blog entry OTLT and EAV: the two big design mistakes all beginners make.