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Tom Lane 0436f6bde8 Disallow set-returning functions inside CASE or COALESCE. 
When we reimplemented SRFs in commit 69f4b9c85, our initial choice was
to allow the behavior to vary from historical practice in cases where a
SRF call appeared within a conditional-execution construct (currently,
only CASE or COALESCE).  But that was controversial to begin with, and
subsequent discussion has resulted in a consensus that it's better to
throw an error instead of executing the query differently from before,
so long as we can provide a reasonably clear error message and a way to
rewrite the query.

Hence, add a parser mechanism to allow detection of such cases during
parse analysis.  The mechanism just requires storing, in the ParseState,
a pointer to the set-returning FuncExpr or OpExpr most recently emitted
by parse analysis.  Then the parsing functions for CASE and COALESCE can
detect the presence of a SRF in their arguments by noting whether this
pointer changes while analyzing their arguments.  Furthermore, if it does,
it provides a suitable error cursor location for the complaint.  (This
means that if there's more than one SRF in the arguments, the error will
point at the last one to be analyzed not the first.  While connoisseurs of
parsing behavior might find that odd, it's unlikely the average user would
ever notice.)

While at it, we can also provide more specific error messages than before
about some pre-existing restrictions, such as no-SRFs-within-aggregates.
Also, reject at parse time cases where a NULLIF or IS DISTINCT FROM
construct would need to return a set.  We've never supported that, but the
restriction is depended on in more subtle ways now, so it seems wise to
detect it at the start.

Also, provide some documentation about how to rewrite a SRF-within-CASE
query using a custom wrapper SRF.

It turns out that the information_schema.user_mapping_options view
contained an instance of exactly the behavior we're now forbidding; but
rewriting it makes it more clear and safer too.

initdb forced because of user_mapping_options change.

Patch by me, with error message suggestions from Alvaro Herrera and
Andres Freund, pursuant to a complaint from Regina Obe.

Discussion: https://postgr.es/m/000001d2d5de$d8d66170$8a832450$@pcorp.us
 		2017-06-13 23:46:39 -04:00
config Update config.guess and config.sub 2017-05-14 11:09:34 -04:00
contrib psql: Use more consistent capitalization of some output headings 2017-06-13 14:41:14 -04:00
doc Disallow set-returning functions inside CASE or COALESCE. 2017-06-13 23:46:39 -04:00
src Disallow set-returning functions inside CASE or COALESCE. 2017-06-13 23:46:39 -04:00
.dir-locals.el emacs: Set indent-tabs-mode in perl-mode 2015-04-12 23:53:23 -04:00
.gitattributes Remove contrib/tsearch2. 2017-02-13 11:06:11 -05:00
.gitignore Allow .so minor version numbers above 9 in .gitignore. 2016-08-15 17:35:35 -04:00
COPYRIGHT Update copyright for 2017 2017-01-03 12:37:53 -05:00
GNUmakefile.in Have "make coverage" recurse into contrib as well 2016-09-05 18:44:36 -03:00
HISTORY Change documentation references to PG website to use https: not http: 2017-05-20 21:50:47 -04:00
Makefile Allow make check in PL directories 2011-02-15 06:52:12 +02:00
README Change documentation references to PG website to use https: not http: 2017-05-20 21:50:47 -04:00
README.git Change documentation references to PG website to use https: not http: 2017-05-20 21:50:47 -04:00
aclocal.m4 ICU support 2017-03-23 15:28:48 -04:00
configure Stamp 10beta1. 2017-05-15 17:20:59 -04:00
configure.in Stamp 10beta1. 2017-05-15 17:20:59 -04:00

README 

PostgreSQL Database Management System
=====================================

This directory contains the source code distribution of the PostgreSQL
database management system.

PostgreSQL is an advanced object-relational database management system
that supports an extended subset of the SQL standard, including
transactions, foreign keys, subqueries, triggers, user-defined types
and functions.  This distribution also contains C language bindings.

PostgreSQL has many language interfaces, many of which are listed here:

	https://www.postgresql.org/download

See the file INSTALL for instructions on how to build and install
PostgreSQL.  That file also lists supported operating systems and
hardware platforms and contains information regarding any other
software packages that are required to build or run the PostgreSQL
system.  Copyright and license information can be found in the
file COPYRIGHT.  A comprehensive documentation set is included in this
distribution; it can be read as described in the installation
instructions.

The latest version of this software may be obtained at
https://www.postgresql.org/download/.  For more information look at our
web site located at https://www.postgresql.org/.