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Overview
| Comment: | Improve the example of how to create a new aggregate window function in windowfunctions.in. |
|---|---|
| Timelines: | family | ancestors | descendants | both | trunk |
| Files: | files | file ages | folders |
| SHA3-256: |
873c1ea4b70a2dc29b5354c853909d55 |
| User & Date: | dan 2018-06-26 17:48:46 |
Context
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2018-06-30
| ||
| 20:23 | Create a change log for version 3.25.0 check-in: 5697c09027 user: drh tags: trunk | |
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2018-06-26
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| 17:48 | Improve the example of how to create a new aggregate window function in windowfunctions.in. check-in: 873c1ea4b7 user: dan tags: trunk | |
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2018-06-25
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| 20:35 | Add documentation for implementing new aggregate window functions. check-in: b5a81b3bdf user: dan tags: trunk | |
Changes
Changes to pages/windowfunctions.in.
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return sqlite3_create_window_function(db, "sumint", 1, SQLITE_UTF8, 0,
sumintStep, sumintFinal, sumintValue, sumintInverse, 0
);
}
}
</tcl>
</codeblock>
|
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return sqlite3_create_window_function(db, "sumint", 1, SQLITE_UTF8, 0,
sumintStep, sumintFinal, sumintValue, sumintInverse, 0
);
}
}
</tcl>
</codeblock>
<p> The following example uses the sumint() function implemented by the above
C code. For each row, the window consists of the preceding row (if any), the current row and the following row (again, if any):
<codeblock>
CREATE TABLE t3(x, y);
INSERT INTO t3 VALUES('a', 4),
('b', 5),
('c', 3),
('d', 8),
('e', 1);
<i>-- Assuming the database is populated using the above script, the </i>
<i>-- following SELECT statement returns:</i>
<i>-- </i>
<i>-- x | sum_y</i>
--------------
<i>-- a | 9 </i>
<i>-- b | 12 </i>
<i>-- c | 16 </i>
<i>-- d | 12 </i>
<i>-- e | 9 </i>
<i>-- </i>
SELECT x, sumint(y) OVER (
ORDER BY x ROWS BETWEEN 1 PRECEDING AND 1 FOLLOWING
) AS sum_y
FROM t3 ORDER BY x;
</codeblock>
<p>In processing the query above, SQLite invokes the sumint callbacks as
follows:
<p>
<ol>
<li> <b>xStep(4)</b> - add "4" to the current window.
<li> <b>xStep(5)</b> - add "5" to the current window.
<li> <b>xValue()</b> - invoke xValue() to obtain the value of sumint() for
the row with (x='a'). The window currently consists of values 4 and 5,
and so the result is 9.
<li> <b>xStep(3)</b> - add "3" to the current window.
<li> <b>xValue()</b> - invoke xValue() to obtain the value of sumint() for
the row with (x='b'). The window currently consists of values 4, 5 and
3, and so the result is 12.
<li> <b>xInverse(4)</b> - remove "4" from the window.
<li> <b>xStep(8)</b> - add "8" to the current window. The window now consists
of values 5, 3 and 8.
<li> <b>xValue()</b> - invoked to obtain the value for the row with (x='c').
In this case, 16.
<li> <b>xInverse(5)</b> - remove value "5" from the window.
<li> <b>xStep(1)</b> - add value "1" to the window.
<li> <b>xValue()</b> - invoked to obtain the value for row (x='d').
<li> <b>xInverse(3)</b> - remove value "3" from the window. The window now
contains values 8 and 1 only.
<li> <b>xValue()</b> - invoked to obtain the value for row (x='d'). 9.
</ol>
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