doc: Clarify status of SELECT INTO on reference page

The documentation as well as source code comments weren't entirely
clear whether SELECT INTO was truly deprecated (thus in theory
destined to be removed eventually), or just a less recommended
variant.  After discussion, it appears that other implementations also
use SELECT INTO in direct SQL in a way similar to PostgreSQL, so it
seems worth keeping it for compatibility.  Update the language in the
documentation to that effect.

Discussion: https://www.postgresql.org/message-id/flat/96dc0df3-e13a-a85d-d045-d6e2c85218da%40enterprisedb.com

diff --git a/doc/src/sgml/ref/select_into.sgml b/doc/src/sgml/ref/select_into.sgml
index 7b327d9eeef326a4ff13e24c472a9b5ac82f7668..acc6401485b77599f577980be81e306261f250b4 100644 (file)
--- a/doc/src/sgml/ref/select_into.sgml
+++ b/doc/src/sgml/ref/select_into.sgml
@@ -138,9 +138,11 @@ SELECT * INTO films_recent FROM films WHERE date_prod >= '2002-01-01';
    in <application>ECPG</application> (see <xref linkend="ecpg"/>) and
    <application>PL/pgSQL</application> (see <xref linkend="plpgsql"/>).
    The <productname>PostgreSQL</productname> usage of <command>SELECT
-   INTO</command> to represent table creation is historical.  It is
-   best to use <command>CREATE TABLE AS</command> for this purpose in
-   new code.
+   INTO</command> to represent table creation is historical.  Some other SQL
+   implementations also use <command>SELECT INTO</command> in this way (but
+   most SQL implementations support <command>CREATE TABLE AS</command>
+   instead).  Apart from such compatibility considerations, it is best to use
+   <command>CREATE TABLE AS</command> for this purpose in new code.
   </para>
  </refsect1>