ROWNUM Functions

ROWNUM, INST_NUM

ROWNUM
INST_NUM()

The ROWNUM function returns the number representing the order of the records that will be generated by the query result. The first result record is assigned 1, and the second result record is assigned 2.

Return type:INT

ROWNUM and INST_NUM() can be used in the SELECT statement; ORDERBY_NUM() can be used in the SELECT statement with ORDER BY clauses, and GROUPBY_NUM() can be used in the SELECT statement with GROUP BY clauses. The ROWNUM function can be used to limit the number of result records of the query in several ways. For example, it can be used to search only the first 10 records or to return even or odd number records.

The ROWNUM function has a result value as an integer, and can be used wherever an expression is valid such as the SELECT or WHERE clause. However, it is not allowed to compare the result of the ROWNUM function with the attribute or the correlated subquery.

Note

  • The ROWNUM function specified in the WHERE clause works the same as the INST_NUM() function.
  • The ROWNUM function belongs to each SELECT statement. That is, if a ROWNUM function is used in a subquery, it returns the sequence of the subquery result while it is being executed. Internally, the result of the ROWNUM function is generated right before the searched record is written to the query result set. At this moment, the counter value that generates the serial number of the result set records increases.
  • If you want to add a sequence on the SELECT result; use ROWNUM when there is no sorting process; use ORDERBY_NUM() when there is an ORDER BY clause; use GROUPBY_NUM() function when there is a GROUP BY clause.
  • If an ORDER BY clause is included in the SELECT statement, the value of the ORDERBY_NUM() function specified in the WHERE clause is generated after sorting for the ORDER BY clause.
  • If a GROUP BY clause is included in the SELECT statement, the value of the GROUPBY_NUM() function specified in the HAVING clause is calculated after the query results are grouped.
  • For the purpose of limiting the sorted result rows, instead of FOR ORDERBY_NUM() or HAVING GROUPBY_NUM(), LIMIT clause can be used.
  • The ROWNUM function can also be used in SQL statements such as INSERT, DELETE and UPDATE in addition to the SELECT statement. For example, as in the query INSERT INTO table_name SELECTFROMWHERE …, you can search for part of the row from one table and then insert it into another by using the ROWNUM function in the WHERE clause.

The following example shows how to retrieve country names ranked first to fourth based on the number of gold (gold) medals in the 1988 Olympics in the demodb database.

--Limiting 4 rows using ROWNUM in the WHERE condition
SELECT  * FROM
(SELECT nation_code FROM participant WHERE host_year = 1988
     ORDER BY gold DESC) AS T
WHERE ROWNUM <5;
  nation_code
======================
  'URS'
  'GDR'
  'USA'
  'KOR'

LIMIT clause limits the sorted result rows; therefore, the below result is the same as the above.

--Limiting 4 rows using LIMIT
SELECT ROWNUM, nation_code FROM participant WHERE host_year = 1988
ORDER BY gold DESC
LIMIT 4;
       rownum  nation_code
===================================
          156  'URS'
          155  'GDR'
          154  'USA'
          153  'KOR'

ROWNUM condition in the below limits before sorting; therefore, the result is different from the above.

--Unexpected results : ROWNUM operated before ORDER BY
SELECT ROWNUM, nation_code FROM participant
WHERE host_year = 1988 AND ROWNUM < 5
ORDER BY gold DESC;
       rownum  nation_code
===================================
            1  'ZIM'
            2  'ZAM'
            3  'ZAI'
            4  'YMD'

ORDERBY_NUM

ORDERBY_NUM()

The ORDERBY_NUM() function is used with the ROWNUM() or INST_NUM() function to limit the number of result rows. The difference is that the ORDERBY_NUM() function is combined after the ORDER BY clause to give order to a result that has been already sorted. That is, when retrieving only some of the result rows by using ROWNUM in a condition clause of the SELECT statement that includes the ORDER BY clause, ROWNUM is applied first and then group sorting by ORDER BY is performed. On the other hand, when retrieving only some of the result rows by using the ORDER_NUM() function, ROWNUM is applied to the result of sorting by ORDER BY.

Return type:INT

The following example shows how to retrieve athlete names ranked 3rd to 5th and their records in the history table in the demodb database.

--Ordering first and then limiting rows using FOR ORDERBY_NUM()
SELECT ORDERBY_NUM(), athlete, score FROM history
ORDER BY score FOR ORDERBY_NUM() BETWEEN 3 AND 5;
    orderby_num()  athlete               score
==============================================================
                3  'Luo Xuejuan'         '01:07.0'
                4  'Rodal Vebjorn'       '01:43.0'
                5  'Thorpe Ian'          '01:45.0'

The following query using a LIMIT clause outputs the same result with the above query.

SELECT ORDERBY_NUM(), athlete, score FROM history
ORDER BY score LIMIT 2, 3;

The following query using ROWNUM limits the result rows before sorting; then ORDER BY sorting is operated.

--Limiting rows first and then Ordering using ROWNUM
SELECT athlete, score FROM history
WHERE ROWNUM BETWEEN 3 AND 5 ORDER BY score;
  athlete               score
============================================
  'Thorpe Ian'          '01:45.0'
  'Thorpe Ian'          '03:41.0'
  'Hackett Grant'       '14:43.0'

GROUPBY_NUM

GROUPBY_NUM()

The GROUPBY_NUM() function is used with the ROWNUM or INST_NUM() function to limit the number of result rows. The difference is that the GROUPBY_NUM() function is combined after the GROUP BY … HAVING clause to give order to a result that has been already sorted. In addition, while the INST_NUM() function is a scalar function, the GROUPBY_NUM() function is kind of an aggregate function.

That is, when retrieving only some of the result rows by using ROWNUM in a condition clause of the SELECT statement that includes the GROUP BY clause, ROWNUM is applied first and then group sorting by GROUP BY is performed. On the other hand, when retrieving only some of the result rows by using the GROUPBY_NUM() function, ROWNUM is applied to the result of group sorting by GROUP BY.

Return type:INT

The following example shows how to retrieve the fastest record in the previous five Olympic Games from the history table in the demodb database.

--Group-ordering first and then limiting rows using GROUPBY_NUM()
SELECT  GROUPBY_NUM(), host_year, MIN(score) FROM history
GROUP BY host_year HAVING GROUPBY_NUM() BETWEEN 1 AND 5;
    groupby_num()    host_year  min(score)
=====================================================
                1         1968  '8.9'
                2         1980  '01:53.0'
                3         1984  '13:06.0'
                4         1988  '01:58.0'
                5         1992  '02:07.0'

The following query using a LIMIT clause outputs the same result with the above query.

SELECT  GROUPBY_NUM(), host_year, MIN(score) FROM history
GROUP BY host_year LIMIT 5;

The following query using ROWNUM limits the result rows before grouping; then GROUP BY operation is performed.

--Limiting rows first and then Group-ordering using ROWNUM
SELECT host_year, MIN(score) FROM history
WHERE ROWNUM BETWEEN 1 AND 5 GROUP BY host_year;
    host_year  min(score)
===================================
         2000  '03:41.0'
         2004  '01:45.0'