Updating fields in sql incrementing by 1 each time - sql

Question

I am trying to construct an SQL query that would take a set of rows and renumber a field on all rows, starting at where they all match a session ID.
e.g.
before change:
SessionID | LineNumber | LineContents
----------------------------------------------
74666 | 1 | example content
74666 | 2 | some other content
74666 | 3 | another line
74666 | 4 | final line
after change (user has deleted line 2 so the 'LineNumber' values have updated to reflect the new numbering (i.e. line '3' has now become line '2' etc.):
SessionID | LineNumber | LineContents
----------------------------------------------
74666 | 1 | example content
74666 | 2 | another line
74666 | 3 | final line
So reflecting this in NON proper syntax would be something along these lines
i = 0;
UPDATE tbl_name
SET LineNumber = i++;
WHERE SessionID = 74666;
Searches a lot for this with no luck, any help is great :)

Answer 1

Using Row_Number() function and CTE:
;WITH CTE AS (
SELECT SessionID, LineNumber, LineContents,
Row_Number() OVER(PARTITION BY SessionID ORDER BY LineNumber) Rn
FROM Table1
)
UPDATE CTE
SET LineNumber = Rn
WHERE SessionID = 74666;
Fiddle Demo

Answer 2

You can use ROW_NUMBER ( MS SQL ) or ROWNUM ( Oracle ) or similar inside your UPDATE statement.
Check this
Or this

Answer 3

You have 2 main ways to do that.
The first "low level" way is this one (SQL Fiddle here):
DELETE FROM TestTable
WHERE SESSIONID = 74666 AND LineNumber = 3;
UPDATE TestTable SET LineNumber = LineNumber-1
WHERE SESSIONID = 74666 AND LineNumber > 3
select * from TestTable -- check the result
Here we're assuming you know both LineNumber and SessionID.
The other way is through t-SQL Triggers, a little more complex but it helps you if you don't know info about the rows you're deleting. Give it a try.

Answer 4

CREATE TABLE Trial (
-- ID INT,
SessionID INT ,
LineNumber INT ,
LineContent NVARCHAR(100)
)
INSERT INTO dbo.trial
VALUES ( 74666, 1, 'example content' ) ,
( 74666, 2, 'some other content' ),
( 74666, 4, 'another line' ),
( 74666, 5, 'final line' )
You can last deleted LineNumber value and can use that id in your update statement to update rest of the LineNumbers , for instance here Linenumber 3 is deleted so ,
UPDATE dbo.trial SET LineNumber = LineNumber -1 WHERE LineNumber > 3

Answer 5

I would be really inclined to handle this differently if at all possible, and have the Linenumber generated on the fly, to avoid having to maintain a column, e.g.:
CREATE TABLE dbo.T
(
LineNumberID INT IDENTITY(1, 1) NOT NULL PRIMARY KEY,
SessionID INT NOT NULL,
LineContents NVARCHAR(MAX) NOT NULL
);
GO
INSERT dbo.T (SessionID, LineContents)
VALUES
(74666, 'example content'),
(74666, 'some other content'),
(74666, 'another line'),
(74666, 'final line');
GO
CREATE VIEW dbo.V
AS
SELECT LinenumberID,
SessionID,
Linenumber = ROW_NUMBER() OVER(PARTITION BY SessionID ORDER BY LinenumberID),
LineContents
FROM dbo.T;
GO
In this your View gives you what you need, and if I delete as follows:
SELECT *
FROM dbo.V;
DELETE dbo.V
WHERE SessionID = 74666
AND Linenumber = 3;
SELECT *
FROM dbo.V;
You get the output:
LINENUMBERID SESSIONID LINENUMBER LINECONTENTS
1 74666 1 example content
2 74666 2 some other content
3 74666 3 another line
4 74666 4 final line
LINENUMBERID SESSIONID LINENUMBER LINECONTENTS
1 74666 1 example content
2 74666 2 some other content
4 74666 3 final line
Example on SQL Fiddle
So you maintain your sequential linenumber field without actually having to update a field. This of course only works if you can rely on a field (such as CreatedDate, or an ID column) to order by. Otherwise you will have to maintain it using triggers, and update statements as suggested in other answers.