How do I use ROW_NUMBER()?

问题:

I want to use the ROW_NUMBER() to get...

1. To get the max(ROW_NUMBER()) --> Or i guess this would also be the count of all rows

I tried doing:

SELECT max(ROW_NUMBER() OVER(ORDER BY UserId)) FROM Users

but it didn't seem to work...

2. To get ROW_NUMBER() using a given piece of information, ie. if I have a name and I want to know what row the name came from.

I assume it would be something similar to what I tried for #1

SELECT ROW_NUMBER() OVER(ORDER BY UserId) From Users WHERE UserName='Joe'

but this didn't work either...

Any Ideas?

回答1:

For the first question, why not just use?

SELECT COUNT(*) FROM myTable 

to get the count.

And for the second question, the primary key of the row is what should be used to identify a particular row. Don't try and use the row number for that.

---

If you returned Row_Number() in your main query,

SELECT ROW_NUMBER() OVER (Order by Id) AS RowNumber, Field1, Field2, Field3
FROM User

Then when you want to go 5 rows back then you can take the current row number and use the following query to determine the row with currentrow -5

SELECT us.Id
FROM (SELECT ROW_NUMBER() OVER (ORDER BY id) AS Row, Id
     FROM User ) us 
WHERE Row = CurrentRow - 5   

回答2:

Though I agree with others that you could use count() to get the total number of rows, here is how you can use the row_count():

1. To get the total no of rows:

   with temp as (
       select row_number() over (order by id) as rownum
       from table_name 
   )
   select max(rownum) from temp

2. To get the row numbers where name is Matt:

   with temp as (
       select name, row_number() over (order by id) as rownum
       from table_name
   )
   select rownum from temp where name like 'Matt'

You can further use min(rownum) or max(rownum) to get the first or last row for Matt respectively.

These were very simple implementations of row_number(). You can use it for more complex grouping. Check out my response on Advanced grouping without using a sub query

回答3:

If you need to return the table's total row count, you can use an alternative way to the SELECT COUNT(*) statement.

Because SELECT COUNT(*) makes a full table scan to return the row count, it can take very long time for a large table. You can use the sysindexes system table instead in this case. There is a ROWS column that contains the total row count for each table in your database. You can use the following select statement:

SELECT rows FROM sysindexes WHERE id = OBJECT_ID('table_name') AND indid < 2

This will drastically reduce the time your query takes.

回答4:

ROW_NUMBER() returns a unique number for each row starting with 1. You can easily use this by simply writing:

ROW_NUMBER() OVER (ORDER BY 'Column_Name' DESC) as ROW_NUMBER

You can find the difference between Row_number(), Rank() and Dense_Rank() here.

回答5:

SELECT num, UserName FROM 
 (SELECT UserName, ROW_NUMBER() OVER(ORDER BY UserId) AS num
  From Users) AS numbered
WHERE UserName='Joe'

回答6:

If you absolutely want to use ROW_NUMBER for this (instead of count(*)) you can always use:

SELECT TOP 1 ROW_NUMBER() OVER (ORDER BY Id)   
FROM USERS  
ORDER BY ROW_NUMBER() OVER (ORDER BY Id) DESC

回答7:

You can use Row_Number for limit query result.

Example:

SELECT * FROM (
    select row_number() OVER (order by createtime desc) AS ROWINDEX,* 
    from TABLENAME ) TB
WHERE TB.ROWINDEX between 0 and 10

-- With above query, I will get PAGE 1 of results from TABLENAME.

回答8:

May not be related to the question here. But I found it could be useful when using ROW_NUMBER -

SELECT *,
ROW_NUMBER() OVER (ORDER BY (SELECT 100)) AS Any_ID 
FROM #Any_Table

回答9:

select 
  Ml.Hid,
  ml.blockid,
  row_number() over (partition by ml.blockid order by Ml.Hid desc) as rownumber,
  H.HNAME 
from MIT_LeadBechmarkHamletwise ML
join [MT.HAMLE] h on ML.Hid=h.HID

回答10:

This query:

SELECT ROW_NUMBER() OVER(ORDER BY UserId) From Users WHERE UserName='Joe'

will return all rows where the UserName is 'Joe' UNLESS you have no UserName='Joe'

They will be listed in order of UserID and the row_number field will start with 1 and increment however many rows contain UserName='Joe'

If it does not work for you then your WHERE command has an issue OR there is no UserID in the table. Check spelling for both fields UserID and UserName.

回答11:

You can use this for get first record where has clause

SELECT TOP(1)*,ROW_NUMBER() OVER(ORDER BY UserId) AS rownum FROM Users WHERE UserName='Joe' ORDER BY rownum asc

回答12:

SQL Row_Number() function is to sort and assign an order number to data rows in related record set. So it is used to number rows, for example to identify the top 10 rows which have the highest order amount or identify the order of each customer which is the highest amount, etc.

If you want to sort the dataset and number each row by seperating them into categories we use Row_Number() with Partition By clause. For example, sorting orders of each customer within itself where the dataset contains all orders, etc.

SELECT
    SalesOrderNumber,
    CustomerId,
    SubTotal,
    ROW_NUMBER() OVER (PARTITION BY CustomerId ORDER BY SubTotal DESC) rn
FROM Sales.SalesOrderHeader

But as I understand you want to calculate the number of rows of grouped by a column. To visualize the requirement, if you want to see the count of all orders of the related customer as a seperate column besides order info, you can use COUNT() aggregation function with Partition By clause

For example,

SELECT
    SalesOrderNumber,
    CustomerId,
    COUNT(*) OVER (PARTITION BY CustomerId) CustomerOrderCount
FROM Sales.SalesOrderHeader

回答13:

Need to create virtual table by using "WITH table AS", which is mention in given Query.

By using this virtual table, you can perform CRUD operation w.r.t row_number.

QUERY:

WITH table AS
-
(SELECT row_number() OVER(ORDER BY UserId) rn, * FROM Users)
-
SELECT * FROM table WHERE UserName='Joe'
-

You can use INSERT, UPDATE or DELETE in last sentence by in spite of SELECT.