SQL RANK versus ROW NUMBER

Question

I m confused about the differences between these   Running the following SQL gets me two idential result sets   Can someone please explain the differences   SELECT ID   Description   RANK         OVER PARTITION BY StyleID ORDER BY ID  as  Rank       FROM SubStyle SELECT ID   Description   ROW NUMBER   OVER PARTITION BY StyleID ORDER BY ID  as  RowNumber  FROM SubStyle

User · Answer

You will only see the difference if you have ties within a partition for a particular ordering value.

RANK and DENSE_RANK are deterministic in this case, all rows with the same value for both the ordering and partitioning columns will end up with an equal result, whereas ROW_NUMBER will arbitrarily (non deterministically) assign an incrementing result to the tied rows.

Example: (All rows have the same StyleID so are in the same partition and within that partition the first 3 rows are tied when ordered by ID)

WITH T(StyleID, ID)
     AS (SELECT 1,1 UNION ALL
         SELECT 1,1 UNION ALL
         SELECT 1,1 UNION ALL
         SELECT 1,2)
SELECT *,
       RANK() OVER(PARTITION BY StyleID ORDER BY ID)       AS 'RANK',
       ROW_NUMBER() OVER(PARTITION BY StyleID ORDER BY ID) AS 'ROW_NUMBER',
       DENSE_RANK() OVER(PARTITION BY StyleID ORDER BY ID) AS 'DENSE_RANK'
FROM   T

Returns

StyleID     ID       RANK      ROW_NUMBER      DENSE_RANK
----------- -------- --------- --------------- ----------
1           1        1         1               1
1           1        1         2               1
1           1        1         3               1
1           2        4         4               2

You can see that for the three identical rows the ROW_NUMBER increments, the RANK value remains the same then it leaps to 4. DENSE_RANK also assigns the same rank to all three rows but then the next distinct value is assigned a value of 2.

User · Answer

ROW NUMBER   Returns a unique number for each row starting with 1  For rows that have duplicate values numbers are arbitarily assigned   Rank   Assigns a unique number for each row starting with 1 except for rows that have duplicate values in which case the same ranking is assigned and a gap appears in the sequence for each duplicate ranking

User · Answer

Also  pay attention to ORDER BY in PARTITION  Standard AdventureWorks db is used for example  when using RANK      SELECT    as1 SalesOrderID    as1 SalesOrderDetailID      RANK   OVER    PARTITION BY as1 SalesOrderID ORDER BY as1 SalesOrderID   ranknoequal         RANK   OVER  PARTITION BY as1 SalesOrderID ORDER BY   as1 SalesOrderDetailId   ranknodiff  FROM Sales SalesOrderDetail as1   WHERE SalesOrderId   43659 ORDER BY SalesOrderDetailId    Gives result    SalesOrderID    SalesOrderDetailID  rank same as partition  rank salesorderdetailid 43659   1   1   1 43659   2   1   2 43659   3   1   3 43659   4   1   4 43659   5   1   5 43659   6   1   6 43659   7   1   7 43659   8   1   8 43659   9   1   9 43659   10  1   10 43659   11  1   11 43659   12  1   12   But if change order by to  use OrderQty       SELECT    as1 SalesOrderID    as1 OrderQty    RANK   OVER  PARTITION BY   as1 SalesOrderID ORDER BY as1 SalesOrderID   ranknoequal      RANK     OVER  PARTITION BY as1 SalesOrderID ORDER BY as1 OrderQty   rank orderqty   FROM Sales SalesOrderDetail as1 WHERE SalesOrderId   43659 ORDER BY   OrderQty    Gives    SalesOrderID    OrderQty    rank salesorderid   rank orderqty 43659   1   1   1 43659   1   1   1 43659   1   1   1 43659   1   1   1 43659   1   1   1 43659   1   1   1 43659   2   1   7 43659   2   1   7 43659   3   1   9 43659   3   1   9 43659   4   1   11 43659   6   1   12   Notice how the Rank changes when we use OrderQty  rightmost column second table  in ORDER BY and how it changes when we use SalesOrderDetailID  rightmost column first table  in ORDER BY

User · Answer

Simple query without partition clause   select      sal       RANK   over order by sal desc  as Rank      DENSE RANK   over order by sal desc  as DenseRank      ROW NUMBER   over order by sal desc  as RowNumber from employee    Output       -------- ------- ----------- ----------     sal      Rank    DenseRank   RowNumber     -------- ------- ----------- ----------     5000     1       1           1     3000     2       2           2     3000     2       2           3     2975     4       3           4     2850     5       4           5     -------- ------- ----------- ----------

User · Answer

Look this example   CREATE TABLE  dbo   TestTable       id   int  NOT NULL       create date   date  NOT NULL       info1   varchar  50  NOT NULL       info2   varchar  50  NOT NULL      Insert some data  INSERT INTO dbo  TestTable  id  create date  info1  info2  VALUES  1   1 1 09    Blue    Green   INSERT INTO dbo  TestTable  id  create date  info1  info2  VALUES  1   1 2 09    Red    Yellow   INSERT INTO dbo  TestTable  id  create date  info1  info2  VALUES  1   1 3 09    Orange    Purple   INSERT INTO dbo  TestTable  id  create date  info1  info2  VALUES  2   1 1 09    Yellow    Blue   INSERT INTO dbo  TestTable  id  create date  info1  info2  VALUES  2   1 5 09    Blue    Orange   INSERT INTO dbo  TestTable  id  create date  info1  info2  VALUES  3   1 2 09    Green    Purple   INSERT INTO dbo  TestTable  id  create date  info1  info2  VALUES  3   1 8 09    Red    Blue     Repeat same Values for 1     INSERT INTO dbo  TestTable  id  create date  info1  info2  VALUES  1     1 1 09    Blue    Green     Look All  SELECT   FROM  TestTable   Look your results   SELECT Id      create date      info1      info2      ROW NUMBER   OVER  PARTITION BY Id ORDER BY create date DESC  AS RowId      RANK   OVER PARTITION BY Id ORDER BY create date DESC     AS  RANK  FROM  TestTable   Need to understand the different

User · Answer

I haven t done anything with rank  but I discovered this today with row number     select item  name  sold  row number   over partition by item order by sold  as row from table name   This will result in some repeating row numbers since in my case each name holds all items  Each item will be ordered by how many were sold    -------- ------ ----- ----   glasses  store1   30   1     glasses  store2   35   2     glasses  store3   40   3     shoes    store2   10   1     shoes    store1   20   2     shoes    store3   22   3     -------- ------ ----- ----

User · Answer

This article covers an interesting relationship between ROW NUMBER   and DENSE RANK    the RANK   function is not treated specifically   When you need a generated ROW NUMBER   on a SELECT DISTINCT statement  the ROW NUMBER   will produce distinct values before they are removed by the DISTINCT keyword  E g  this query  SELECT DISTINCT   v     ROW NUMBER   OVER  ORDER BY v  row number FROM t ORDER BY v  row number       might produce this result  DISTINCT has no effect     --- ------------    V   ROW NUMBER    --- ------------    a            1     a            2     a            3     b            4     c            5     c            6     d            7     e            8    --- ------------    Whereas this query   SELECT DISTINCT   v     DENSE RANK   OVER  ORDER BY v  row number FROM t ORDER BY v  row number       produces what you probably want in this case    --- ------------    V   ROW NUMBER    --- ------------    a            1     b            2     c            3     d            4     e            5    --- ------------    Note that the ORDER BY clause of the DENSE RANK   function will need all other columns from the SELECT DISTINCT clause to work properly   The reason for this is that logically  window functions are calculated before DISTINCT is applied   All three functions in comparison  Using PostgreSQL   Sybase   SQL standard syntax  WINDOW clause    SELECT   v    ROW NUMBER   OVER  window  row number    RANK         OVER  window  rank    DENSE RANK   OVER  window  dense rank FROM t WINDOW window AS  ORDER BY v  ORDER BY v       you ll get    --- ------------ ------ ------------    V   ROW NUMBER   RANK   DENSE RANK    --- ------------ ------ ------------    a            1      1            1     a            2      1            1     a            3      1            1     b            4      4            2     c            5      5            3     c            6      5            3     d            7      7            4     e            8      8            5    --- ------------ ------ ------------

User · Answer

Quite a bit   The rank of a row is one plus the number of ranks that come before the row in question   Row number is the distinct rank of rows  without any gap in the ranking   http   www bidn com blogs marcoadf bidn-blog 379 ranking-functions-row number-vs-rank-vs-dense rank-vs-ntile

[sql] SQL RANK() versus ROW_NUMBER()

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