initial commit

Author: Vik Fearing

.gitattributes

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+sql/* linguist-language=SQL
+expected/* linguist-detectable=false

.gitignore

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+.vscode/
+test_current.sh

.travis.yml

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+# run the testsuite on travis-ci.com
+---
+# versions to run on
+env:
+  - PG_SUPPORTED_VERSIONS=9.6
+  - PG_SUPPORTED_VERSIONS=10
+  - PG_SUPPORTED_VERSIONS=11
+  - PG_SUPPORTED_VERSIONS=12
+  - PG_SUPPORTED_VERSIONS=13
+
+language: C
+dist: bionic
+
+before_install:
+  - sudo apt-get update -qq
+
+install:
+  # upgrade postgresql-common for new apt.postgresql.org.sh
+  - sudo apt-get install -y postgresql-common
+  - sudo /usr/share/postgresql-common/pgdg/apt.postgresql.org.sh -p -v $PG_SUPPORTED_VERSIONS -i
+  - sudo apt-get install -y postgresql-contrib-$PG_SUPPORTED_VERSIONS
+
+script:
+  - make
+  - sudo make install
+  - pg_virtualenv make installcheck
+  - if test -s regression.diffs; then cat regression.diffs; fi

CODE_OF_CONDUCT.md

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+This extension adheres to the official [PostgreSQL Community Code of
+Conduct](https://www.postgresql.org/about/policies/coc/). It is not
+reproduced here so that future modifications may take effect
+immediately.

LICENSE

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+PostgreSQL License
+
+Copyright (c) 2019, The PostgreSQL Global Development Group (PGDG)
+
+Permission to use, copy, modify, and distribute this software and its
+documentation for any purpose, without fee, and without a written agreement is
+hereby granted, provided that the above copyright notice and this paragraph
+and the following two paragraphs appear in all copies.
+
+IN NO EVENT SHALL PGDG BE LIABLE TO ANY PARTY FOR DIRECT, INDIRECT,
+SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING LOST PROFITS, ARISING
+OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN IF PGDG
+HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+PGDG SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
+PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS ON AN "AS IS" BASIS,
+AND PGDG HAS NO OBLIGATIONS TO PROVIDE MAINTENANCE, SUPPORT, UPDATES,
+ENHANCEMENTS, OR MODIFICATIONS.

Makefile

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+MODULES = extra_window_functions
+EXTENSION = extra_window_functions
+DOCS = README.extra_window_functions
+
+DATA = extra_window_functions--1.0.sql
+
+REGRESS = regression
+
+PG_CONFIG = pg_config
+PGXS := $(shell $(PG_CONFIG) --pgxs)
+include $(PGXS)

README.extra_window_functions

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+README.md

README.md

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+# Extra Window Functions for PostgreSQL
+
+[![License](https://img.shields.io/badge/license-PostgreSQL-blue)](https://www.postgresql.org/about/licence/)
+[![Code of Conduct](https://img.shields.io/badge/code%20of%20conduct-PostgreSQL-blueviolet)](https://www.postgresql.org/about/policies/coc/)
+
+[![Travis Build Status](https://api.travis-ci.com/xocolatl/extra_window_functions.svg?branch=master)](https://travis-ci.com/xocolatl/extra_window_functions)
+
+*compatible 9.6–13*
+
+This extension provides additional window functions to PostgreSQL.  Some of
+them provide SQL Standard functionality but without the SQL Standard grammar,
+others extend on the SQL Standard, and still others are novel and hopefully
+useful to someone.
+
+## Simualating Standard SQL
+
+The window functions `LEAD()`, `LAG()`, `FIRST_VALUE()`, `LAST_VALUE()`, and
+`NTH_VALUE()` can skip over null values.  PostgreSQL does not implement the
+syntax required for that feature but this extension provides additional
+functions that give you the same behavior.
+
+In addition to this, `NTH_VALUE()` can count from the start or the end of the
+window frame.
+
+Despite these functions having long names, there isn't really any difference in
+length compared to the excessively verbose SQL Standard syntax.
+
+```
+-- Standard SQL:
+NTH_VALUE(x, 3) FROM LAST IGNORE NULLS OVER w
+
+-- This extension:
+nth_value_from_last_ignore_nulls(x, 3) OVER w
+```
+
+## Extending Standard SQL
+
+The functions `LEAD()` and `LAG()` accept a default value for when the
+requested row falls outside of the partition.  However, the functions
+`FIRST_VALUE()`, `LAST_VALUE()`, and `NTH_VALUE()` do not have default values
+for when the requested row is not in the frame.
+
+## Non-Standard Functions
+
+This extension introduces a new partition-level window function `flip_flop()`
+and implements the
+"[flip floperator](https://en.wikipedia.org/wiki/Flip-flop_(programming))".
+
+In the first variant, the function returns false until the expression given as
+an argument returns true.  It then keeps returning true until expression is
+matched again.  The second variant takes two expressions: the first to flip,
+the second to flop.