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21c window function enhancements (#47)
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‎features/_versions/21.3.adoc‎

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= 21.3
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Oracle Database 21c was first released in August 2021.
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== Marquee Features
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* JSON Data Type
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* Blockchain Tables
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* SQL Macros
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* Enhanced Analytic Functions
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For more information about all the new features in this release, see link:https://docs.oracle.com/en/database/oracle/oracle-database/21/nfcon/introduction.html[Oracle Database 21c New Features].

‎features/window-clause.adoc‎

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= WINDOW clause
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:database-version: 21.3
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:database-category: sql
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[[feature_summary]]
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The `WINDOW` clause enables you to define `PARTITION BY`, `ORDER BY`, and window frames for analytic functions. You can use these named windows in the `OVER` clause of functions in the `SELECT` clause.
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[source,sql]
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[subs="verbatim"]
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----
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alter session set nls_date_format = 'DD-MON-YYYY';
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select employee_id,
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department_id, salary,
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-- these calculate totals per department
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count (*) over ( dept_w ) emps_per_dept,
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sum ( salary ) over ( dept_w ) wages_per_dept,
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hire_date,
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-- this gets the running total of salaries/dept in order they were hired
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sum ( salary ) over ( hired_w ) cumul_sal,
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-- this gets the moving average of salaries for the last four hires/dept
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round ( avg ( salary ) over last_four ) rolling_mean
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from hr.employees
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where department_id < 50
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window dept_w as (
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-- split by department
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partition by department_id
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), hired_w as (
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-- sort by date hired
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dept_w order by hire_date
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), last_four as (
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-- include the previous three rows & current
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hired_w rows 3 preceding
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);
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----
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.Result
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[source,sql]
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[subs="verbatim"]
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----
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SQL> alter session set nls_date_format = 'DD-MON-YYYY';
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Session altered.
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SQL> select employee_id,
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2 department_id, salary,
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3 -- these calculate totals per department
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4 count (*) over ( dept_w ) emps_per_dept,
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5 sum ( salary ) over ( dept_w ) wages_per_dept,
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6 hire_date,
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7 -- this gets the running total of salaries/dept in order they were hired
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8 sum ( salary ) over ( hired_w ) cumul_sal,
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9 -- this gets the moving average of salaries for the last four hires/dept
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10 round ( avg ( salary ) over last_four ) rolling_mean
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11 from hr.employees
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12 where department_id < 50
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13 window dept_w as (
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14 -- split by department
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15 partition by department_id
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16 ), hired_w as (
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17 -- sort by date hired
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18 dept_w order by hire_date
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19 ), last_four as (
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20 -- include the previous three rows & current
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21 hired_w rows 3 preceding
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22 );
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EMPLOYEE_ID DEPARTMENT_ID SALARY EMPS_PER_DEPT WAGES_PER_DEPT HIRE_DATE CUMUL_SAL ROLLING_MEAN
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----------- ------------- ---------- ------------- -------------- ----------- ---------- ------------
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200 10 4400 1 4400 17-SEP-2013 4400 4400
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201 20 13000 2 19000 17-FEB-2014 13000 13000
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202 20 6000 2 19000 17-AUG-2015 19000 9500
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114 30 11000 6 24900 07-DEC-2012 11000 11000
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115 30 3100 6 24900 18-MAY-2013 14100 7050
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117 30 2800 6 24900 24-JUL-2015 16900 5633
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116 30 2900 6 24900 24-DEC-2015 19800 4950
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118 30 2600 6 24900 15-NOV-2016 22400 2850
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119 30 2500 6 24900 10-AUG-2017 24900 2700
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203 40 6500 1 6500 07-JUN-2012 6500 6500
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10 rows selected.
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----
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== Benefits
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The `WINDOW` clause enables you to define common windows once and reuse them in a statement. This makes queries easier to maintain.
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== Further information
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* Availability: All Offerings
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* https://docs.oracle.com/en/database/oracle/oracle-database/21/dwhsg/sql-analysis-reporting-data-warehouses.html#GUID-2877E1A5-9F11-47F1-A5ED-D7D5C7DED90A[Documentation]

‎features/window-functions-exclusion-frame.adoc‎

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= Window functions frame exclusion
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:database-version: 21.3
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:database-category: sql
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[[feature_summary]]
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Use frame exclusion to omit rows from the calculation in window functions. This has four options:
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* `EXCLUDE CURRENT ROW` - remove the row being processed from the calculation.
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* `EXCLUDE GROUP` - omit all rows with the same value for the window's `ORDER BY` columns as the current row
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* `EXCLUDE TIES` - omit all other rows with the same value for the window's `ORDER BY` columns from the total as the current row, but include the current row
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* `EXCLUDE NO OTHERS` - Include all rows in the window in the calculation. This is the default.
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[source,sql]
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[subs="verbatim"]
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----
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alter session set nls_date_format = 'DD-MON-YYYY';
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select hire_date
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, count(*) over (
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-- include all previous rows; default
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hire_w rows unbounded preceding exclude no others
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) include_all
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, count(*) over (
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-- omit this row from the count
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hire_w rows unbounded preceding exclude current row
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) omit_current
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, count(*) over (
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-- omit all rows with the same value for hire_date as this
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hire_w rows unbounded preceding exclude group
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) omit_group
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, count(*) over (
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-- omit other rows with the same value for hire_date as this
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hire_w rows unbounded preceding exclude ties
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) omit_ties
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from hr.employees
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where hire_date >= date'2015-03-03'
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window hire_w as ( order by hire_date )
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fetch first 5 rows only;
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----
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.Result
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[source,sql]
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[subs="verbatim"]
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----
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SQL> alter session set nls_date_format = 'DD-MON-YYYY';
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Session altered.
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SQL> select hire_date
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2 , count(*) over (
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3 -- include all previous rows; default
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4 hire_w rows unbounded preceding exclude no others
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5 ) include_all
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6 , count(*) over (
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7 -- omit this row from the count
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8 hire_w rows unbounded preceding exclude current row
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9 ) omit_current
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10 , count(*) over (
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11 -- omit all rows with the same value for hire_date as this
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12 hire_w rows unbounded preceding exclude group
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13 ) omit_group
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14 , count(*) over (
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15 -- omit other rows with the same value for hire_date as this
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16 hire_w rows unbounded preceding exclude ties
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17 ) omit_ties
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18 from hr.employees
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19 where hire_date >= date'2015-03-03'
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20 window hire_w as ( order by hire_date )
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21 fetch first 5 rows only;
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HIRE_DATE INCLUDE_ALL OMIT_CURRENT OMIT_GROUP OMIT_TIES
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----------- ----------- ------------ ---------- ----------
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03-MAR-2015 1 0 0 1
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10-MAR-2015 2 1 1 2
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10-MAR-2015 3 2 1 2
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11-MAR-2015 4 3 3 4
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19-MAR-2015 5 4 4 5
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----
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== Benefits
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Frame exclusion simplifies SQL statements that need to remove rows from running total and moving window calculations
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== Further information
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* Availability: All Offerings
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* https://docs.oracle.com/en/database/oracle/oracle-database/21/dwhsg/sql-analysis-reporting-data-warehouses.html#GUID-2877E1A5-9F11-47F1-A5ED-D7D5C7DED90A[Documentation]

‎features/window-functions-groups-frame.adoc‎

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= Window functions GROUPS frame
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:database-version: 21.3
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:database-category: sql
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[[feature_summary]]
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The `GROUPS` frame enables you to get running totals over the previous N sort values in window functions.
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This in addition to the existing `ROWS` and `RANGE` frames. The differences between these are:
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* `ROWS :N PRECEDING` - include the current row and up to N rows before it
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* `RANGE :N PRECEDING` - include all rows between _current_ - N and _current_; _current_ is the value of the `ORDER BY` column for the row the function is processing
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* `GROUPS :N PRECEDING` - include all rows with the same value and previous N unique values for the columns in the window's `ORDER BY`
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[source,sql]
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[subs="verbatim"]
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----
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alter session set nls_date_format = 'DD-MON-YYYY';
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select hire_date
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-- include current & three previous rows
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, count(*) over ( order by hire_date rows 3 preceding ) prev3_rows
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-- include all rows between hire_date - 3 and hire_date for the current row
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, count(*) over ( order by hire_date range 3 preceding ) prev3_days
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-- include all rows with the any of the previous three and current hire_dates
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, count(*) over ( order by hire_date groups 3 preceding ) prev3_values
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from hr.employees
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where hire_date >= date'2015-03-03'
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fetch first 5 rows only;
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----
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.Result
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[source,sql]
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[subs="verbatim"]
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----
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SQL> alter session set nls_date_format = 'DD-MON-YYYY';
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Session altered.
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SQL> select hire_date
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2 -- include current & three previous rows
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3 , count(*) over ( order by hire_date rows 3 preceding ) prev3_rows
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4 -- include all rows between hire_date - 3 and hire_date for the current row
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5 , count(*) over ( order by hire_date range 3 preceding ) prev3_days
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6 -- include all rows with the any of the previous three and current hire_dates
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7 , count(*) over ( order by hire_date groups 3 preceding ) prev3_values
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8 from hr.employees
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9 where hire_date >= date'2015-03-03'
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10 fetch first 5 rows only;
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HIRE_DATE PREV3_ROWS PREV3_DAYS PREV3_VALUES
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----------- ---------- ---------- ------------
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03-MAR-2015 1 1 1
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10-MAR-2015 2 2 3
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10-MAR-2015 3 2 3
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11-MAR-2015 4 3 4
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19-MAR-2015 4 1 5
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----
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== Benefits
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The `GROUPS` frame simplifies SQL statements that need to calculate running totals over the previous N unique values.
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== Further information
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* Availability: All Offerings
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* https://docs.oracle.com/en/database/oracle/oracle-database/21/dwhsg/sql-analysis-reporting-data-warehouses.html#GUID-2877E1A5-9F11-47F1-A5ED-D7D5C7DED90A[Documentation]

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