My question might be better understood if I provide a (simplified) example of the scenario. I have two tables, Event and Course. The Event table contains EventID, CourseID, and EventDate. The Course table contains CourseID, and CourseName.
I would like to add a new Event. I understand that the query normally would be as follows:
INSERT INTO event
(EventID,CourseID,EventDate) VALUES ( NULL,'2','2011-03-01');
But instead I would like to update Event by providing the CourseName instead of CourseID. How would I go about doing this?
Edit: Apparently there isn't a way to do this with just a MYSQL query. I'm trying to do this in PHP and attempting to allow a user to update the Event record. Obviously it would be convenient for the user to add a new event based on the name of the course, preferably with a dropdown box.
Thanks
INSERT INTO Event ( EventID, CourseID, EventDate )
SELECT NULL, C.CourseID, '2011-03-01'
FROM Course C
WHERE C.CourseName = 'Course Name Goes Here';
This one one thing that you could try. Though you may want to include the date in your query or some other way to make sure you are uniquely identifying the record you are looking for.
Another thing that you could think about is storing the event id, when you bring up the reference to the event you would like the user to update. Then you would ensure that you are only updating the record that you intend to.
update Event set ....
where courseID=(
select courseID from Course
where CourseName like ''
)
Related
In my project I have got the following tables:
Event (id, title, date, user_id)
Group (id, name, creator_id)
User (id, name, email,...)
group_user (group_id, user_id)
In the application a user can have a personal event or a group can have a event that will be shared will all users in the group.
A user is able to create an event , then the events user_id is this users ID.
Now i would like to create an event within a group - so I need a relationship between the event and the group.
Should I create the attribute group_id in the event table and leave it empty if the event just belongs to a user and not to a group?
Or should I consider creating a new table like groupEvent which has got the attribute group_id.
Or should I create a pivot table group_event that contains the groupID and the eventID as attributes.
Thanks for your help!!
One way I could think of is for you to get rid of the user_id foreign key in the Event table and instead have a User_Event table that maps users and events and a Group_Event table that maps groups and events. Not sure if this is the best design for your use case but this will avoid the need for two foreign keys in the Event table (of which one of them is NULL for every row).
Create 2 separate table Group_Event(id,group-id,event-id) and User_Event(id,user-id,event-id).
Advantages of this method is that
querying will be very easy.
you can add multiple events for a user.
you can add multiple events for a group.
But you should make sure that while adding an event to Group_Event
you should also add the same event to User_Event WHERE "User_Event.user-id" = "group_user.user_id" AND "group_user.group_id" = "Group_Event.group-id".
I am searching for the answer of this question by many days. There are some answers on stackoverflow and on ther sites which I really don't understand. Basically I need to insert only if cell value for particular column does not exist.
Ex: See below table, if their are some duplicate names present it's ok like 'sandy' and 'edward'. But for some names like 'wilson' I don't want to insert. I don't want to make name column unique at all.
Note : Please don't give any complicated answer or procedural queries, it should be easy to remember.
you should make another column/table to determine which name can't duplicate
Then, you select the name whether can be duplicate or not from that table and then insert based on result
You can make a checkbox at HTML FORM.
You fill form values
If that checkbox checked, then before inserting in database, it will will check if exists then no insertion. If not exists then insert.
If that checkbox is not checked, then insert blindly
try the following:
INSERT INTO info (id, name)
SELECT null, 'wilson' FROM any_other_table_name
WHERE NOT EXISTS (
SELECT name FROM info WHERE name = 'wilson'
) ;
It will not insert if multiple entry.
In master table I have two field named 'id-->AutpIncrement,Primary key','designation-->varchar'.In registration table 'designation-->INT,Foreign key of Id in designation table'.Now what I have to do is that I have to fire select query i.e. select id from designation where name=;something like this and than have to store it using String.getParameter.After doing all this have to pass result set query
i.e. rs.getInt(1);
and finally int id have to insert.
And one thing more in registration form designation is in drop down menu and done coding as dynamic means designation details appear on the web browser by fetching information from database.
Please help me in code for select and than passing information by insert as I have defined in first paragraph .
I'm planning to log referral clicks in mysql by the country of the IP.
Let's say my table is named referral_clicks and has the columns id, referral_id, country.
I have 2 approaches in mind now:
Create another column clicks which is set to +1 for every country / referral_id. This means that I would have to check first if the row for the specific referral_id and country already exists and if not, create it.
Insert a new row for every request. My concern here is, that the table might geht messy and too big, as might get very much referral requests.
What would be the best approach now for something like that, or is there evern a better approach?
Use INSERT ... ON DUPLICATE KEY UPDATE.
I suggest you create a table with the following columns.
id (autoincrement)
referral_id
country
clickdate
clicks
I suggest you create a unique index of (referral_id,country,clickdate).
Then, I suggest you use the following SQL each time you want to log a click:
INSERT INTO referral_clicks (referral_id, country, clickdate, clicks)
VALUES ('whatever', 'whatcountry', CURDATE(), 1)
ON DUPLICATE KEY UPDATE clicks=click+1
This will start a new row for each referral id, for each country, for each date. If the row already exists it will increment clicks for you.
I have 2 tables - one storing user information (id, username, password) and the second one storing information about events (id, name, description, date, username(represents the user who created the event)). I would like to implement 'favourite events' functionality. This would allow the user to store his favourite events and later display them in a list. I am not sure how to implement this in terms of design. I need a simple solution. Something like storing the IDs of favourite events in a field in the user table. I am using mysql and PHP. Can anyone point me to the right direction?
You want to have a table linking the foreign keys from the user and event tables.
Users Table:
id, username, password
Events Table:
id, name, description, date, username
Favorites Table:
id, user_id, event_id
This way you can easily access the list of favorite events.
SELECT events.name, events.description, events.date
FROM events, users, favorites
WHERE favorites.user_id = users.id
AND favorites.event_id = events.id
What you need is the most classic and basic many-to-many relationship.
You'll need extra table (let's say: user_event_ref) that will store user and event ids.
User:
id
name
Event:
id
name
UserEventRef:
user_id
event_id
In usereventref each column is a Foreign Key, and both columns are parts of Primary Key.
There's always the option to add a tiny-int field to the Events table flagging an event as a favorite. This doesn't violate normalization in that whether or not an even is a favorite has no effect on the other events. It has the added benefit of automatically deleting the event from favorites if the event is deleted.
If a sorting scheme is needed for the favorites you can still modify the events table in the same manner. If details about the "favorite" such as when it was added to the list etc is needed then you should use an additional table as suggested.