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The main motivation for changing this is bug #4921, in which it's pointed out that it's no longer safe to apply ltree operations to the result of ARRAY(SELECT ...) if the sub-select might return no rows. Before 8.3, the ARRAY() construct would return NULL, which might or might not be helpful but at least it wouldn't result in an error. Now it returns an empty array which results in a failure for no good reason, since the ltree operations are all perfectly capable of dealing with zero-element arrays. As far as I can find, these ltree functions are the only places where zero array dimensionality is rejected unnecessarily. Back-patch to 8.3 to prevent behavioral regression of queries that worked in older releases.
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: http://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. Changes between all PostgreSQL releases are recorded in the file HISTORY. 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 http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.