ROW NUMBER in MySQL

Question

Is there a nice way in MySQL to replicate the SQL Server function ROW NUMBER     For example   SELECT      col1  col2       ROW NUMBER   OVER  PARTITION BY col1  col2 ORDER BY col3 DESC  AS intRow FROM Table1   Then I could  for example  add a condition to limit intRow to 1 to get a single row with the highest col3 for each  col1  col2  pair

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From MySQL 8 0 0 and above you could natively use windowed functions   1 4 What Is New in MySQL 8 0      Window functions         MySQL now supports window functions that  for each row from a query  perform a calculation using rows related to that row  These include functions such as RANK    LAG    and NTILE    In addition  several existing aggregate functions now can be used as window functions  for example  SUM   and AVG       ROW NUMBER   over clause       Returns the number of the current row within its partition  Rows numbers range from 1 to the number of partition rows       ORDER BY affects the order in which rows are numbered  Without ORDER BY  row numbering is indeterminate     Demo   CREATE TABLE Table1    id INT AUTO INCREMENT PRIMARY KEY  col1 INT col2 INT  col3 TEXT    INSERT INTO Table1 col1  col2  col3  VALUES  1 1  a    1 1  b    1 1  c            2 1  x    2 1  y    2 2  z     SELECT      col1  col2 col3      ROW NUMBER   OVER  PARTITION BY col1  col2 ORDER BY col3 DESC  AS intRow FROM Table1    DBFiddle Demo

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This could also be a solution   SET  row number   0   SELECT        row number   row number   1  AS num  firstName  lastName FROM     employees

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This allows the same functionality that ROW NUMBER   AND PARTITION BY provides to be achieved in MySQL  SELECT   row num    IF  prev value GENDER  row num 1 1  AS RowNumber        FirstName          Age         Gender          prev value    GENDER   FROM Person         SELECT  row num    1  x         SELECT  prev value        y   ORDER BY Gender  Age DESC

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There is no ranking functionality in MySQL   The closest you can get is to use a variable   SELECT t             rownum     rownum   1 AS rank   FROM YOUR TABLE t           SELECT  rownum    0  r        so how would that work in my case  I d need two variables  one for each of col1 and col2  Col2 would need resetting somehow when col1 changed      Yes   If it were Oracle  you could use the LEAD function to peak at the next value   Thankfully  Quassnoi covers the logic for what you need to implement in MySQL

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I want the row with the single highest col3 for each  col1  col2  pair    That s a groupwise maximum  one of the most commonly-asked SQL questions  since it seems like it should be easy  but actually it kind of isn t    I often plump for a null-self-join   SELECT t0 col3 FROM table AS t0 LEFT JOIN table AS t1 ON t0 col1 t1 col1 AND t0 col2 t1 col2 AND t1 col3 gt t0 col3 WHERE t1 col1 IS NULL       Get the rows in the table for which no other row with matching col1 col2 has a higher col3      You will notice this and most other groupwise-maximum solutions will return multiple rows if more than one row has the same col1 col2 col3  If that s a problem you may need some post-processing

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There is no funtion like rownum  row num   in MySQL but the way around is like below   select         s   s 1 serial no         tbl    from my table tbl   select  s  0  as s

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Important  Please consider upgrading to MySQL 8  and use the defined and documented ROW NUMBER   function  and ditch old hacks tied to a feature limited ancient version of MySQL  Now here s one of those hacks   The answers here that use in-query variables mostly all seem to ignore the fact that the documentation says  paraphrase       Don t rely on items in the SELECT list being evaluated in order from top to bottom  Don t assign variables in one SELECT item and use them in another one   As such  there s a risk they will churn out the wrong answer  because they typically do a   select    row number variable that uses partition variable      assign partition variable    If these are ever evaluated bottom up  the row number will stop working  no partitions   So we need to use something with a guaranteed order of execution  Enter CASE WHEN   SELECT   t        r    CASE      WHEN col    prevcol THEN  r   1      WHEN   prevcol    col    null THEN null     ELSE 1 END AS rn FROM   t      SELECT  r    0   prevcol    null  x ORDER BY col   As outline ld  order of assignment of prevcol is important - prevcol has to be compared to the current row s value before we assign it a value from the current row  otherwise it would be the current rows col value  not the previous row s col value     Here s how this fits together    The first WHEN is evaluated  If this row s col is the same as the previous row s col then  r is incremented and returned from the CASE  This return led values is stored in  r  It s a feature of MySQL that assignment returns the new value of what is assigned into  r into the result rows   For the first row on the result set   prevcol is null  it is initialised to null in the subquery  so this predicate is false  This first predicate also returns false every time col changes  current row is different to previous row   This causes the second WHEN to be evaluated   The second WHEN predicate is always false  and it exists purely to assign a new value to  prevcol  Because this row s col is different to the previous row s col  we know this because if it were the same  the first WHEN would have been used   we have to assign the new value to keep it for testing next time  Because the assignment is made and then the result of the assignment is compared with null  and anything equated with null is false  this predicate is always false  But at least evaluating it did its job of keeping the value of col from this row  so it can be evaluated against the next row s col value  Because the second WHEN is false  it means in situations where the column we are partitioning by  col  has changed  it is the ELSE that gives a new value for  r  restarting the numbering from 1   We this get to a situation where this   SELECT   t       ROW NUMBER   OVER PARTITION BY pcol1  pcol2      pcolX ORDER BY ocol1  ocol2      ocolX  rn FROM   t   Has the general form   SELECT   t        r    CASE      WHEN col1    pcol1 AND col2    pcol2 AND     AND colX    pcolX THEN  r   1      WHEN   pcol1    pcol1    null OR   pcol2    col2    null OR     OR   pcolX    colX    null THEN null     ELSE 1    END AS rn FROM   t      SELECT  r    0   pcol1    null   pcol2    null        pcolX    null  x ORDER BY pcol1  pcol2       pcolX  ocol1  ocol2       ocolX   Footnotes     The p in pcol means  partition   the o in ocol means  order  - in the general form I dropped the  prev  from the variable name to reduce visual clutter  The brackets around   pcolX    colX    null are important  Without them you ll assign null to  pcolX and things stop working  It s a compromise that the result set has to be ordered by the partition columns too  for the previous column compare to work out  You can t thus have your rownumber ordered according to one column but your result set ordered to another You might be able to resolve this with subqueries but I believe the docs also state that subquery ordering may be ignored unless LIMIT is used and this could impact performance  I haven t delved into it beyond testing that the method works  but if there is a risk that the predicates in the second WHEN will be optimised away  anything compared to null is null false so why bother running the assignment  and not executed  it also stops  This doesn t seem to happen in my experience but I ll gladly accept comments and propose solution if it could reasonably occur It may be wise to cast the nulls that create  pcolX to the actual types of your columns  in the subquery that creates the  pcolX variables  viz  select  pcol1    CAST null as INT    pcol2    CAST null as DATE

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A bit late but may also help to someone who looks for answers     Between rows row number example - recursive query that may be used in any SQL   WITH data row num  some val  AS     SELECT 1 row num  1 some val FROM any table --dual in Oracle   UNION ALL  SELECT row num 1  some val row num FROM data WHERE row num  lt  20 -- any number   SELECT   FROM data  WHERE row num BETWEEN 5 AND 10    ROW NUM    SOME VAL ------------------- 5           11 6           16 7           22 8           29 9           37 10          46

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MariaDB 10 2 is implementing  Window Functions   including RANK    ROW NUMBER   and several other things   https   mariadb com kb en mariadb window-functions   Based on a talk at Percona Live this month  they are reasonably well optimized   The syntax is identical to the code in the Question

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SELECT       i   i 1 AS iterator       t   FROM      tablename AS t       SELECT  i  0  AS foo

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MySQL has supported the ROW NUMBER   since version 8 0    If you use MySQL 8 0 or later  check it out ROW NUMBER   function   Otherwise  you have emulate ROW NUMBER   function   The  row number   is a ranking function that returns a sequential number of a row  starting from 1 for the first row    for older version   SELECT t             rowid     rowid   1 AS ROWID   FROM TABLE t           SELECT  rowid    0  dummy

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query for row number in mysql  set  row number 0  select   row number     row number  1  as num id name from sbs

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I don t see any simple answer covering the  PARTITION BY  part so here s mine    SELECT       FROM       select         CASE WHEN  partitionBy 1   l THEN  row number   row number 1 ELSE  row number  1 END AS i            partitionBy 1  l AS p           t       from           select  row number  0  partitionBy 1  null       as x     cross join           select 1 as n   a  as l         union all         select 1 as n   b  as l             union all         select 2 as n   b  as l             union all         select 2 as n   a  as l         union all         select 3 as n   a  as l             union all             select 3 as n   b  as l           as t     ORDER BY l  n   AS X where i  gt  1    The ORDER BY clause must reflect your ROW NUMBER need  Thus there s already a clear limitation  you can t have several ROW NUMBER  emulation  of this form at the same time  The order of the  computed column  matters  If you have mysql compute those column in another order  it might not work  In this simple example I only put one but you can have several  PARTITION BY  parts      CASE WHEN  partitionBy 1   part1 AND  partitionBy 2   part2       THEN  row number   row number 1 ELSE  row number  1 END AS i        partitionBy 1  part1 AS P1        partitionBy 2  part2 AS P2            FROM       SELECT  row number  0  partitionBy 1  null  partitionBy 2  null        as x

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The solution I found to work the best was using a subquery like this   SELECT      col1  col2                 SELECT COUNT             FROM Table1         WHERE col1   t1 col1         AND col2   t1 col2         AND col3  gt  t1 col3       AS intRow FROM Table1 t1   The PARTITION BY columns just get compared with     and separated by AND   The ORDER BY columns would be compared with   lt   or      and separated by OR   I ve found this to be very flexible  even if it is a little bit costly

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I would also vote for Mosty Mostacho s solution with minor modification to his query code   SELECT a i  a j        SELECT count    from test b where a j  gt   b j AND a i   b i   AS row number FROM test a   Which will give the same result    ------ ------ ------------       i      j   row number    ------ ------ ------------       1     11            1        1     12            2        1     13            3        2     21            1        2     22            2        2     23            3        3     31            1        3     32            2        3     33            3        4     14            1    ------ ------ ------------    for the table    ------ ------       i      j    ------ ------       1     11        1     12        1     13        2     21        2     22        2     23        3     31        3     32        3     33        4     14    ------ ------    With the only difference that the query doesn t use JOIN and GROUP BY  relying on nested select instead

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Also a bit late but today I had the same need so I did search on Google and finally a simple  general approach found here in Pinal Dave s article http   blog sqlauthority com 2014 03 09 mysql-reset-row-number-for-each-group-partition-by-row-number   I wanted to focus on Paul s original question  that was my problem as well  so I summarize my solution as a working example   Beacuse we want to partition over two column I would create a SET variable during the iteration to identify if a new group was started   SELECT col1  col2  col3 FROM     SELECT col1  col2  col3            n    CASE WHEN  v   MAKE SET 3  col1  col2                      THEN  n   1 -- if we are in the same group                     ELSE 1 -- next group starts so we reset the counter                 END AS row number            v    MAKE SET 3  col1  col2  -- we store the current value for next iteration     FROM Table1   SELECT  n    0   v    NULL  r -- helper table for iteration with startup values    ORDER BY col1  col2  col3 DESC -- because we want the row with maximum value   x WHERE row number   1 -- and here we select exactly the wanted row from each group   The 3 means at the first parameter of MAKE SET that I want both value in the SET  3 1 2   Of course if we do not have two or more columns constructing the groups we can eliminate the MAKE SET operation  The construction is exactly the same  This is working for me as required  Many thanks to Pinal Dave for his clear demonstration

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The rownumber functionality can t be mimicked  You might get the results you expect  but you ll most likely get disappointed at some stage  Here s what mysql documentation says      For other statements  such as SELECT  you might get the results you expect  but this is not guaranteed  In the following statement  you might think that MySQL will evaluate  a first and then do an assignment second    SELECT  a   a   a 1         However  the order of evaluation for expressions involving user variables is undefined     Regards  Georgi

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Check out this Article  it shows how to mimic SQL ROW NUMBER   with a partition by in MySQL    I ran into this very same scenario in a WordPress Implementation  I needed ROW NUMBER   and it wasn t there    http   www explodybits com 2011 11 mysql-row-number   The example in the article is using a single partition by field  To partition by additional fields you could do something like this      SELECT   row num    IF  prev value concat ws    t col1 t col2   row num 1 1  AS RowNumber           t col1            t col2           t Col3           t col4            prev value    concat ws    t col1 t col2      FROM table1 t            SELECT  row num    1  x            SELECT  prev value        y    ORDER BY t col1 t col2 t col3 t col4    Using concat ws handles null s  I tested this against 3 fields using an int  date  and varchar  Hope this helps  Check out the article as it breaks this query down and explains it

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This is not the most robust solution - but if you re just looking to create a partitioned rank on a field with only a few different values  it may not be unwieldily to use some case when logic with as many variables as you require    Something like this has worked for me in the past   SELECT t        CASE WHEN  lt partition field gt     rownum1     rownum1   1       WHEN  lt partition field gt     rownum2     rownum2   1                END AS rank FROM YOUR TABLE t       SELECT  rownum1    0  r1   SELECT  rownum2    0  r2 ORDER BY  lt rank order by field gt      Hope that makes sense   helps

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I always end up following this pattern  Given this table    ------ ------       i      j    ------ ------       1     11        1     12        1     13        2     21        2     22        2     23        3     31        3     32        3     33        4     14    ------ ------    You can get this result    ------ ------ ------------       i      j   row number    ------ ------ ------------       1     11            1        1     12            2        1     13            3        2     21            1        2     22            2        2     23            3        3     31            1        3     32            2        3     33            3        4     14            1    ------ ------ ------------    By running this query  which doesn t need any variable defined   SELECT a i  a j  count    as row number FROM test a JOIN test b ON a i   b i AND a j  gt   b j GROUP BY a i  a j   Hope that helps

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This Work perfectly for me to create RowNumber when we have more than one column   In this case two column   SELECT  row num    IF  prev value  concat  Fk Business Unit Code   NetIQ Job Code     row num 1  1  AS RowNumber        Fk Business Unit Code           NetIQ Job Code          Supervisor Name          prev value    concat  Fk Business Unit Code   NetIQ Job Code     FROM  SELECT DISTINCT  Fk Business Unit Code   NetIQ Job Code   Supervisor Name                 FROM Employee           ORDER BY  Fk Business Unit Code    NetIQ Job Code    Supervisor Name  DESC  z     SELECT  row num    1  x     SELECT  prev value        y   ORDER BY  Fk Business Unit Code    NetIQ Job Code   Supervisor Name  DESC

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I would define a function   delimiter    DROP FUNCTION IF EXISTS  getFakeId    CREATE FUNCTION  getFakeId    RETURNS int 11      DETERMINISTIC begin return if  fakeId   fakeId   fakeId 1   fakeId  1   end     then I could do   select getFakeId   as id  t   from table t   select  fakeId  0  as t2    Now you don t have a subquery  which you can t have in views

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Solutions with cross join and comma won t work if your query has GROUP BY statement  For such cases you can use subselect  SELECT   row number     row number   1  AS rowNumber  res   FROM     SELECT SUM r amount     FROM Results r    WHERE username   1    GROUP BY r amount   res CROSS JOIN  SELECT  row number    0  AS dummy

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