Use LEFT JOINs in some system views in case referenced row doesn't exist.

In particular, left join to pg_authid so that rows in pg_stat_activity
don't disappear if the session's owning user has been dropped.
Also convert a few joins to pg_database to left joins, in the same spirit,
though that case might be harder to hit.  We were doing this in other
views already, so it was a bit inconsistent that these views didn't.

Oskari Saarenmaa, with some further tweaking by me

Discussion: <56E87CD8.60007@ohmu.fi>

src/backend/catalog/system_views.sql

@@ -642,9 +642,9 @@ CREATE VIEW pg_stat_activity AS
             S.backend_xid,
             s.backend_xmin,
             S.query
-    FROM pg_database D, pg_stat_get_activity(NULL) AS S, pg_authid U
+    FROM pg_stat_get_activity(NULL) AS S
-    WHERE S.datid = D.oid AND
+        LEFT JOIN pg_database AS D ON (S.datid = D.oid)
-            S.usesysid = U.oid;
+        LEFT JOIN pg_authid AS U ON (S.usesysid = U.oid);
 
 CREATE VIEW pg_stat_replication AS
     SELECT
@@ -664,10 +664,9 @@ CREATE VIEW pg_stat_replication AS
             W.replay_location,
             W.sync_priority,
             W.sync_state
-    FROM pg_stat_get_activity(NULL) AS S, pg_authid U,
+    FROM pg_stat_get_activity(NULL) AS S
-            pg_stat_get_wal_senders() AS W
+        JOIN pg_stat_get_wal_senders() AS W ON (S.pid = W.pid)
-    WHERE S.usesysid = U.oid AND
+        LEFT JOIN pg_authid AS U ON (S.usesysid = U.oid);
-            S.pid = W.pid;
 
 CREATE VIEW pg_stat_wal_receiver AS
     SELECT
@@ -813,7 +812,7 @@ CREATE VIEW pg_stat_progress_vacuum AS
 		S.param4 AS heap_blks_vacuumed, S.param5 AS index_vacuum_count,
 		S.param6 AS max_dead_tuples, S.param7 AS num_dead_tuples
     FROM pg_stat_get_progress_info('VACUUM') AS S
-		 JOIN pg_database D ON S.datid = D.oid;
+		LEFT JOIN pg_database D ON S.datid = D.oid;
 
 CREATE VIEW pg_user_mappings AS
     SELECT
@@ -832,12 +831,11 @@ CREATE VIEW pg_user_mappings AS
             NULL
         END AS umoptions
     FROM pg_user_mapping U
-         LEFT JOIN pg_authid A ON (A.oid = U.umuser) JOIN
+        JOIN pg_foreign_server S ON (U.umserver = S.oid)
-        pg_foreign_server S ON (U.umserver = S.oid);
+        LEFT JOIN pg_authid A ON (A.oid = U.umuser);
 
 REVOKE ALL on pg_user_mapping FROM public;
 
-
 CREATE VIEW pg_replication_origin_status AS
     SELECT *
     FROM pg_show_replication_origin_status();

src/include/catalog/catversion.h

@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	201608171
+#define CATALOG_VERSION_NO	201608191
 
 #endif

src/test/regress/expected/rules.out

@@ -1664,10 +1664,9 @@ pg_stat_activity| SELECT s.datid,
     s.backend_xid,
     s.backend_xmin,
     s.query
-   FROM pg_database d,
+   FROM ((pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, ssl, sslversion, sslcipher, sslbits, sslcompression, sslclientdn)
-    pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, ssl, sslversion, sslcipher, sslbits, sslcompression, sslclientdn),
+     LEFT JOIN pg_database d ON ((s.datid = d.oid)))
-    pg_authid u
+     LEFT JOIN pg_authid u ON ((s.usesysid = u.oid)));
-  WHERE ((s.datid = d.oid) AND (s.usesysid = u.oid));
 pg_stat_all_indexes| SELECT c.oid AS relid,
     i.oid AS indexrelid,
     n.nspname AS schemaname,
@@ -1776,7 +1775,7 @@ pg_stat_progress_vacuum| SELECT s.pid,
     s.param6 AS max_dead_tuples,
     s.param7 AS num_dead_tuples
    FROM (pg_stat_get_progress_info('VACUUM'::text) s(pid, datid, relid, param1, param2, param3, param4, param5, param6, param7, param8, param9, param10)
-     JOIN pg_database d ON ((s.datid = d.oid)));
+     LEFT JOIN pg_database d ON ((s.datid = d.oid)));
 pg_stat_replication| SELECT s.pid,
     s.usesysid,
     u.rolname AS usename,
@@ -1793,10 +1792,9 @@ pg_stat_replication| SELECT s.pid,
     w.replay_location,
     w.sync_priority,
     w.sync_state
-   FROM pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, ssl, sslversion, sslcipher, sslbits, sslcompression, sslclientdn),
+   FROM ((pg_stat_get_activity(NULL::integer) s(datid, pid, usesysid, application_name, state, query, wait_event_type, wait_event, xact_start, query_start, backend_start, state_change, client_addr, client_hostname, client_port, backend_xid, backend_xmin, ssl, sslversion, sslcipher, sslbits, sslcompression, sslclientdn)
-    pg_authid u,
+     JOIN pg_stat_get_wal_senders() w(pid, state, sent_location, write_location, flush_location, replay_location, sync_priority, sync_state) ON ((s.pid = w.pid)))
-    pg_stat_get_wal_senders() w(pid, state, sent_location, write_location, flush_location, replay_location, sync_priority, sync_state)
+     LEFT JOIN pg_authid u ON ((s.usesysid = u.oid)));
-  WHERE ((s.usesysid = u.oid) AND (s.pid = w.pid));
 pg_stat_ssl| SELECT s.pid,
     s.ssl,
     s.sslversion AS version,
@@ -2155,8 +2153,8 @@ pg_user_mappings| SELECT u.oid AS umid,
             ELSE NULL::text[]
         END AS umoptions
    FROM ((pg_user_mapping u
-     LEFT JOIN pg_authid a ON ((a.oid = u.umuser)))
+     JOIN pg_foreign_server s ON ((u.umserver = s.oid)))
-     JOIN pg_foreign_server s ON ((u.umserver = s.oid)));
+     LEFT JOIN pg_authid a ON ((a.oid = u.umuser)));
 pg_views| SELECT n.nspname AS schemaname,
     c.relname AS viewname,
     pg_get_userbyid(c.relowner) AS viewowner,