NTILE groups data by sort order into a variable number of percentile groupings : NTILE « Analytical Functions « Oracle PL/SQL Tutorial

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Oracle PL/SQL Tutorial » Analytical Functions » NTILE 
16. 18. 1. NTILE groups data by sort order into a variable number of percentile groupings
  1. The NTILE function roughly works by dividing the number of rows retrieved into the chosen number of segments.
  2. The percentile is displayed as the segment that the rows fall into.
  3. For example, if you wanted to know which salaries where in the top 25%, the next 25%, the next 25%, and the bottom 25%,
  4. Then the NTILE(4) function is used for that ordering (100%/4 = 25%).
  5. The algorithm for the function distributes the values "evenly."
SQL>
SQL> -- create demo table
SQL> create table Employee(
  2    ID                 VARCHAR2(BYTE)         NOT NULL,
  3    First_Name         VARCHAR2(10 BYTE),
  4    Last_Name          VARCHAR2(10 BYTE),
  5    Start_Date         DATE,
  6    End_Date           DATE,
  7    Salary             Number(8,2),
  8    City               VARCHAR2(10 BYTE),
  9    Description        VARCHAR2(15 BYTE)
 10  )
 11  /

Table created.

SQL>
SQL> -- prepare data
SQL> insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary,  City,       Description)
  2               values ('01','Jason',    'Martin',  to_date('19960725','YYYYMMDD'), to_date('20060725','YYYYMMDD'), 1234.56'Toronto',  'Programmer')
  3  /

row created.

SQL> insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary,  City,       Description)
  2                values('02','Alison',   'Mathews', to_date('19760321','YYYYMMDD'), to_date('19860221','YYYYMMDD'), 6661.78'Vancouver','Tester')
  3  /

row created.

SQL> insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary,  City,       Description)
  2                values('03','James',    'Smith',   to_date('19781212','YYYYMMDD'), to_date('19900315','YYYYMMDD'), 6544.78'Vancouver','Tester')
  3  /

row created.

SQL> insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary,  City,       Description)
  2                values('04','Celia',    'Rice',    to_date('19821024','YYYYMMDD'), to_date('19990421','YYYYMMDD'), 2344.78'Vancouver','Manager')
  3  /

row created.

SQL> insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary,  City,       Description)
  2                values('05','Robert',   'Black',   to_date('19840115','YYYYMMDD'), to_date('19980808','YYYYMMDD'), 2334.78'Vancouver','Tester')
  3  /

row created.

SQL> insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary, City,        Description)
  2                values('06','Linda',    'Green',   to_date('19870730','YYYYMMDD'), to_date('19960104','YYYYMMDD'), 4322.78,'New York',  'Tester')
  3  /

row created.

SQL> insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary, City,        Description)
  2                values('07','David',    'Larry',   to_date('19901231','YYYYMMDD'), to_date('19980212','YYYYMMDD'), 7897.78,'New York',  'Manager')
  3  /

row created.

SQL> insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary, City,        Description)
  2                values('08','James',    'Cat',     to_date('19960917','YYYYMMDD'), to_date('20020415','YYYYMMDD'), 1232.78,'Vancouver', 'Tester')
  3  /

row created.

SQL>
SQL>
SQL>
SQL> -- display data in the table
SQL> select from Employee
  2  /

ID   FIRST_NAME LAST_NAME  START_DAT END_DATE      SALARY CITY       DESCRIPTION
---- ---------- ---------- --------- --------- ---------- ---------- ---------------
01   Jason      Martin     25-JUL-96 25-JUL-06    1234.56 Toronto    Programmer
02   Alison     Mathews    21-MAR-76 21-FEB-86    6661.78 Vancouver  Tester
03   James      Smith      12-DEC-78 15-MAR-90    6544.78 Vancouver  Tester
04   Celia      Rice       24-OCT-82 21-APR-99    2344.78 Vancouver  Manager
05   Robert     Black      15-JAN-84 08-AUG-98    2334.78 Vancouver  Tester
06   Linda      Green      30-JUL-87 04-JAN-96    4322.78 New York   Tester
07   David      Larry      31-DEC-90 12-FEB-98    7897.78 New York   Manager
08   James      Cat        17-SEP-96 15-APR-02    1232.78 Vancouver  Tester

rows selected.

SQL>
SQL> SELECT id, first_name, salary,
  2    NTILE(4OVER(ORDER BY salary descnt
  3  FROM employee
  4  /

ID   FIRST_NAME     SALARY         NT
---- ---------- ---------- ----------
07   David         7897.78          1
02   Alison        6661.78          1
03   James         6544.78          2
06   Linda         4322.78          2
04   Celia         2344.78          3
05   Robert        2334.78          3
01   Jason         1234.56          4
08   James         1232.78          4

rows selected.

SQL>
SQL>
SQL>
SQL> -- clean the table
SQL> drop table Employee
  2  /

Table dropped.
16. 18. NTILE
16. 18. 1. NTILE groups data by sort order into a variable number of percentile groupings
16. 18. 2. Get a clearer picture of the NTILE function
16. 18. 3. NTILE function works from row order after a ranking takes place
16. 18. 4. Nulls with the NTILE function
16. 18. 5. NTile with NULLS LAST
16. 18. 6. NTILE with NULLS FIRST (the default)
16. 18. 7. Using the NTILE() Function
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