I'm a newbie in mysql and have to write a implemention for a custom mysql asp.net identity storage.
I follow this tutorial and the first steps are done.
https://learn.microsoft.com/en-us/aspnet/identity/overview/extensibility/implementing-a-custom-mysql-aspnet-identity-storage-provider
Now i have the follow mysql command:
"Select Roles.Name from UserRoles, Roles where UserRoles.UserId = #userId and UserRoles.RoleId = Roles.Id"
My problem is now that i dont know how the table have to look for this request?
I would say:
Tablename : Roles
Select: Roles and Name? or is it a name?
same with UserRoles.UserID and UserRoles.RoleId
What does the point mean?
Thanks a lot
You question is quite unclear, however, if I understood correctly, you can't figure out clearly how the database schema you are using is structured and what you'll get from this query.
The query you have written SELECTs the data field called Name from the table called Roles. In order to do this, the query uses data coming from two tables: one is the Roles table itself, the other is called UserRoles.
It will extract Names data from the Roles table only for the Roles entries that have the Id field matching with the RoleId field of the entries in the UserRoles table that have the UserId equal to the given #UserId.
In other words, this SELECT query in will give you as a result a list of Names coming from the entries in the Roles table which match the given conditional check, which is what is written after the where SQL condition: where UserRoles.UserId = #userId and UserRoles.RoleId = Roles.Id.
Finally, the point "." in SQL queries is used to disambiguate between fields (or columns, if you want to call it so) with same name but coming from different tables. It is quite common that all the tables have an Id field, for example. You can identify the correct Id field in your database by writing Table1.Id, Table2.Id, and so on. Even if you don't have naming conflicts in your tables columns, adding the table name can be very good for code readability.
Edit:
As other users correctly pointed out in the comments to your question, you should also have a look to what an SQL JOIN operation is. Since you are searching data using information coming from different tables, you are actually doing an implicit JOIN on those tables.
Related
My first mySQL project.
I am migrating a FileMaker DB to mySQL and having trouble with how to efficiently handle duplicate field (column) names from 3 left joined tables, combined with the fact that each table is supplying a large number of columns (50+). I understand the concept of aliasing columns. Is there a better way than to create several hundred alias lines to handle each column from each table? I've searched the site and not found a discussion of handling a large number of columns, which is common in FileMaker DBs...perhaps not in mySQL.
Current code is below, where I created the aliases for only ONE (WebPublish) of the ~50 fields for each of the 3 joined tables:
$query = "SELECT
Artwork.WebPublish as Artwork_WebPublish,
Artist.WebPublish as Artist_WebPublish,
Location.WebPublish as Location_WebPublish
FROM Review
LEFT JOIN Artwork ON Review._kf_ArtworkID = Artwork.__kp_ArtworkID
LEFT JOIN Artist ON Review._kf_ArtistID = Artist.__kp_ArtistID
LEFT JOIN Location ON Review._kf_LocationID = Location.__kp_LocationID
WHERE __kp_ReviewID = ?";
This query produces the desired response for one column from each joined table:
Array
(
[Artwork_WebPublish] => Yes
[Artist_WebPublish] => No
[Location_WebPublish] => Maybe
)
The question is whether I need to expand the aliases the long way to include 49 times more data.
Thanks for you help.
No, there's no SQL syntax for giving column aliases in a "batch" mode, for example applying the table name as a prefix to all columns (by the way, SQLite does support that feature by default).
One way to solve this is to refer to columns by ordinal position instead of by name, in whatever language you use to fetch the results.
Another solution is to define your tables with distinct column names so you avoid the name conflict. Some SQL identifiers, for example constraint names, are already required to be unique within the database they reside in, not only unique within a table. It may be a naming convention you want to use to apply the same rule to column names.
I am a reasonably competent SQL programmer but my skills are still pretty much in the domain of simple INSERT, SELECT, UPDATE statements with an occasional LIKE etc thrown in. What I am currently trying to do is rather more complex. Here is the scenario.
I have three tables.
Table 1, *users* identifies users via a User ID, uid. Users can have one or more sub accounts
Table 2 *accounts* keeps a record of subaccounts for each user with, amongst other things the columns uid and sid where uid is the one defined in the *users* table.
Table 3, *data* is currently storing some data, in a data column that is being associated with a particular subaccount, sid.
The thing I have just realized is that there is no particular reason to block users from using those data across subaccounts. No problem - I can change my data subset search SQL to work with the uid instead. However, given the frequency of such searches, it seems well worth while simply sticking in a uid column in *data*.
To do that I would need to write some smart SQL that would get uid,sid pairs from the *accounts* table and use that information to update the newly created uid column in the data table. This I have to admit is beyond my knowledge of SQL.
I should mention that the system using these data is now in production and has several 100s of users so the option of just acting like they are not there is not available. Not terribly relevant I think but I should mention that uid and sid are alphanumeric strinsg with both columns being indexed.
I would be most grateful to anyone here who might be able to help out with it.
Mysql can do updates based on joins and based on reading of your schema here's what I'd do...
UPDATE accounts a, data d
set d.uid=a.uid
where a.sid=d.sid
and d.uid is NULL
First of all, sorry the way I write, bad English here.
Please, consider the following scenario:
I made my database architecture combining views as such:
Entity City has the columns { city_id, city_name, state_name, ... }
Entity User has the columns { user_id, user_name, user_login, city_id, ... }
Each entity has a view, the city view does not have FK to any other entity, so its a simple select.
User entity have one FK to city entity, so it makes a join with the city entity in the view.
As the following example:
create view vw_user as
select user.user_id,
user.user_name,
user.user_login,
vw_city.*
from user (nolock)
inner join vw_city (nolock) on vw_city.city_id = user.city_id
go
So if you have an entity like user_access with a FK to user, the view of user_access will have an inner join to vw_user, and it will bring up all the columns from user and city entities.
In the end, I just make a query on the view, and it returns the full entity with all the foreign references.
This works great, and make the maintenance procedures very easier, I have a stored procedure that recompile all the views if any change is needed to one of the entities.
But, it has a problem, and I discovered this in a very bad situation, the system that uses this architecture is working very fast and smooth already, and I need to join two entities that share the entity city for example, so it generates a collision of columns, SQL Server does not allow this in views, you can execute a query with collision with no problem, but you can't do it in a view.
So, this is my problem, I need to find a way to fix this, but I can't find an answer to it myself.
The only thing I ended up doing is making a hard-coded view with the columns renamed.
But I want a solution for the entire architecture, something permanent, like an upgrade.
This architecture is followed in code, with C#, so there is a dependence on the column names.
When I read the data from the query, I need to get the data from the column name, so this code can be reused with other classes, doing the same thing that the view does in the query, in the c# code.
So, getting data with ordinal is out of the question.
Any ideas?
Thanks, and sorry, but this is very hard to describe.
Well, just to close the subject, as SMC suggested i have used aliases to identify the columns and the tables in my queries.
So the query looks like this now - using the example from the topic:
Select 1.user_id as 1,
1.user_name as 2,
1.user_login as 3,
1.city_id as 4,
2.city_id as 5,
2.city_name as 6,
2.state_name as 7
from user as 1
inner join city as 2 on 2.city_id = 1.city_id
Just notice the columns 4 and 5, they will not collide now :)
Wen my application makes this query he also make the Classes involved to know their aliases in the current query.
It works fine, solved my problem and i don't need to use views anymore.
In the end, the application is faster then before.
That's it :) hope it helps anybody out there.
It's because the Column Name in each View or Function must be unique. You need to be specific while selecting the column Names. Use Alias and then refer the column Names.
You tried to create VIEW using a single column name more than once in the statement.
Remove * and give explicit column name
I want to try and keep this as one query and not use PHP, but it's proving to be tough.
I have a table called applications, that stores all the applications and some basic information about them.
Then, I have a table with all the types of applications in it, and that table contains a reference to another table which stores more specific data about the specific type of application in question.
select applications.id as appid, applications.category, type.title as type, type.id as tid, type.valuefld, type.tablename
from applications
left join type on applications.typeid=type.id
left join department on type.deptid=department.id
where not isnull(work_cat)
and work_cat != ''
and applications.deleted=0
and datei between '10-04-14' and '11-04-14'
order by type, work_cat
Now, in the old version, there is another query on every single result. Over hundreds of results... that sucks.
This is the query I'd like to integrate so I can get all the data in one result row. (Old is ASP, I'm re-writing it in PHP)
query = "select sum("&adors.fields("valuefld")&") as cost, description from "&adors.fields("tablename")&" where appid = '"&adors.fields("tablename")&"'"
Prepared statements, I'm aware, are the best solution, but for now they are not an option.
You can't do this with a plain SQL query - you need to have a defined set of tables that your query is based on. The fact that your current implementation queries from whatever table is named by tablename from the first result-set means that to get this all in one query, you will have to restructure your data. You have to know what tables you're querying from rather than having it dynamic.
If the reason for these different tables is the different information stored in each requiring different record (column) structures, you might want to look into Key/Value pair storage in a large table. Once you combine the dynamically named ones into a single location you can integrate your two queries together.
I'm thinking about it, which of the following two query types would give me the fastest performance for a user messaging module inside my site:
The first one i thought about is a multi table setup, which has a connection table, and a main table. The connection table holds the connection between accounts, and the messaging table.
In this case a query would look like following, to get some data of the author, and the messages he has sent:
SELECT m.*, a.username
FROM messages AS m
LEFT JOIN connection_table
ON (message_id = m.id)
LEFT JOIN accounts AS a
ON (account_id = a.id)
WHERE m.id = '32341'
Inserting into it is a little bit more "complicated".
My other idea, and in my thought the better solution of this problem is that i store the data i would use in a connection table in the same table where is store the data of the mail. Sounds like i would get lots of duplicated entries, but no, because i have a field which has text type and holds user ids like this: *24*32*249*
If I want to query them, i use the mysql LIKE method. Deleting is an other problem, but for this i have one more field where i store who has deleted the post.
Sad about that i don't know how to join this.
So what would you recommend? Are there other ways?
Sounds like you are using an n:m relation.. if yes, don't put a list of ids in a single column but create a mapping table containing two columns - the primary key of table1 and the primary key of table2. Then selecting, inserting and deleting will all be easy and still cheap.
I wonder how many messages will be send to multiple recipients? It might just be easier to have it all in one table - MessageID, SentFrom, SentTo, Message, and dup it for multiple people. This obviously makes it extremely easy to query.
Definately avoid storing multiple ID's in one field and using LIKE - that'll be a performance killer - go with ThiefMasters suggestion if you want something like that.