CODEWITHSUNDEEP
c#sqlsql-serverdatabasedatabase-design
Simon Kiely
Simon Kiely

Reputation: 6040

Create an unique ID for multiple rows SQL

I have a number of user ID's. I am inserting these into a group table which will contain a column for the user's ID and the group ID. This will allow me to use the query "SELECT user_id FROM groups WHERE group_id = '3';" to retrieve user ID's of all the members of group 3.

My problem is that I currently have a list of all users IDs, which I got from a form, using the statements :

int i = 0;
String[] names = { Request.Form["usernames"]Split(' ') }; //retrieving names from form
List<int> user_ids = new List<int>();
foreach(string name in names){ 
    int user_id = db.QueryValue("SELECT user_id FROM users WHERE username = name");
    user_ids.Add(user_id); //now I have a list of all user_ids
}

I now wish to insert this data into the groups table, where all of the user_id values in the list will have the same group_ID. How can I do this?

//create a group from users
"INSERT INTO group (group_id, user_id) VALUES(?,?);

Upvotes: 1

Views: 3315

Answers (7)

Aaron Bertrand
Aaron Bertrand

Reputation: 280262

Assuming you already know 3, you can do this without pulling the user ids into a local list and then inserting them individually (put in quotes specifically because the OP has their query in a similar string):

"INSERT dbo.group(group_id, user_id) 
   SELECT 3, user_id 
   FROM dbo.users 
   WHERE username = name;"

If you don't already know the group id, then please explain how you determined the group id should be 3.

EDIT based on further info.

CREATE TABLE dbo.Groups
(
  GroupID INT IDENTITY(1,1) PRIMARY KEY, 
  GroupName NVARCHAR(255) NOT NULL UNIQUE
);

CREATE TABLE dbo.GroupUsers
(
  GroupID INT NOT NULL FOREIGN KEY
    REFERENCES dbo.Groups(GroupID),
  UserID INT NOT NULL FOREIGN KEY
    REFERENCES dbo.Users(UserID),
  PRIMARY KEY(GroupID, UserID)
);

Now when you want to create a new group and add users to it:

DECLARE @GroupID INT;
INSERT dbo.Groups(GroupName) SELECT N'whatever (unique)';
SELECT @GroupID = SCOPE_IDENTITY();

Now you can loop through each user id:

INSERT dbo.GroupUsers(GroupID, UserID) SELECT @GroupID, <userid>;

Upvotes: 0

jle
jle

Reputation: 9489

What you are talking about is a many-many relationship. You already have a users table:

**users**
userid
username

You need an additional table in the middle. The group table will just have something like:

**group***
groupid
groupName

You would then have a table in the middle. This table would look something like this:

**user_groups**
userid
groupid

You could still use your code to insert a user,

int i = 0;
String[] names = { Request.Form["usernames"]Split(' ') }; //retrieving names from form
List<int> user_ids = new List<int>();
foreach(string name in names){ 
    int user_id = db.QueryValue("SELECT user_id FROM users WHERE username = name");
    user_ids.Add(user_id); //now I have a list of all user_ids
}

After this, you would insert a group:

insert into group(groupName) values("Sample Group")

Then you could retrieve the group id and use that to insert into user_groups

select groupid from group where groupname="Sample Group"

insert into user_groups(userid,groupid) values(...

Also, the table structure should include primary keys and foreign keys (much like @sixlettervariables' answer)

Upvotes: 4

Naval
Naval

Reputation: 344

Insert Into GroupTable (GroupId, UserID) Select GroupID, USerID from UserTable group by GroupID, UserID)

This would work :)

Upvotes: 0

user7116
user7116

Reputation: 64068

In order to make this cleaner, you'll probably want to refactor your database setup slightly such that a third table relates users to groups:

users      (user_id pk, ...)
groups     (group_id pk, ...)
membership (user_id fk, group_id fk) unique(user_id, group_id)

Visualization of User-Group-Membership relations

When you needed to make a new group you simply insert into the groups table, obtain the group_id, and use that to populate the membership table for each of the users in that group.

Upvotes: 2

jonguenther
jonguenther

Reputation: 1

You can insert all of the User ID's from one table into another using a sub-select and union statement as follows:

INSERT INTO group_table_name([user_id]) SELECT [user_id] FROM table_name
UNION ALL

By the way, you might want to change that table name since "group" is a keyword in SQL Server. Just a tip.

Upvotes: 0

Trevor Pilley
Trevor Pilley

Reputation: 16393

You will need to iterate the user_ids list and do a separate insert statement for each user id.

Upvotes: 0

James Bloomer
James Bloomer

Reputation: 5322

You can use the select as the input to the insert

INSERT INTO group (group_id, user_id)
SELECT 1, user_id FROM users WHERE username in ("name1", name2")

You can join the names array back together with some commas.

Upvotes: 0

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