When displaying a Var that is a reference to a column of an unnamed join,

try to display it as a reference to the underlying column instead.  This
is a legitimate substitution (it wouldn't be for a named join) and it
fixes some cases where the display would otherwise be ambiguous.  Per
example from Sim Zacks.

src/backend/utils/adt/ruleutils.c

@@ -3,7 +3,7 @@
  *				back to source text
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/ruleutils.c,v 1.183 2004/10/17 21:17:27 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/ruleutils.c,v 1.184 2004/10/27 18:09:38 tgl Exp $
  *
  *	  This software is copyrighted by Jan Wieck - Hamburg.
  *
@@ -2558,6 +2558,29 @@ get_names_for_var(Var *var, deparse_context *context,
 		}
 		else if (rte->rtekind == RTE_JOIN)
 		{
+			/*
+			 * If it's an unnamed join, look at the expansion of the alias
+			 * variable.  If it's a simple reference to one of the input
+			 * vars then recursively find the name of that var, instead.
+			 * (This allows correct decompiling of cases where there are
+			 * identically named columns on both sides of the join.)
+			 * When it's not a simple reference, we have to just return
+			 * the unqualified variable name (this can only happen with
+			 * columns that were merged by USING or NATURAL clauses).
+			 */
+			if (var->varattno > 0)
+			{
+				Var		*aliasvar;
+
+				aliasvar = (Var *) list_nth(rte->joinaliasvars,
+											var->varattno-1);
+				if (IsA(aliasvar, Var))
+				{
+					get_names_for_var(aliasvar, context,
+									  schemaname, refname, attname);
+					return;
+				}
+			}
 			/* Unnamed join has neither schemaname nor refname */
 			*refname = NULL;
 		}

src/test/regress/expected/rules.out

@@ -1273,7 +1273,7 @@ drop table cchild;
 --
 SELECT viewname, definition FROM pg_views WHERE schemaname <> 'information_schema' ORDER BY viewname;
          viewname         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                definition                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
---------------------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+--------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  iexit                    | SELECT ih.name, ih.thepath, interpt_pp(ih.thepath, r.thepath) AS exit FROM ihighway ih, ramp r WHERE (ih.thepath ## r.thepath);
  pg_indexes               | SELECT n.nspname AS schemaname, c.relname AS tablename, i.relname AS indexname, t.spcname AS "tablespace", pg_get_indexdef(i.oid) AS indexdef FROM ((((pg_index x JOIN pg_class c ON ((c.oid = x.indrelid))) JOIN pg_class i ON ((i.oid = x.indexrelid))) LEFT JOIN pg_namespace n ON ((n.oid = c.relnamespace))) LEFT JOIN pg_tablespace t ON ((t.oid = i.reltablespace))) WHERE ((c.relkind = 'r'::"char") AND (i.relkind = 'i'::"char"));
  pg_locks                 | SELECT l.relation, l."database", l."transaction", l.pid, l."mode", l.granted FROM pg_lock_status() l(relation oid, "database" oid, "transaction" xid, pid integer, "mode" text, granted boolean);
@@ -1296,7 +1296,7 @@ SELECT viewname, definition FROM pg_views WHERE schemaname <> 'information_schem
  pg_statio_user_indexes   | SELECT pg_statio_all_indexes.relid, pg_statio_all_indexes.indexrelid, pg_statio_all_indexes.schemaname, pg_statio_all_indexes.relname, pg_statio_all_indexes.indexrelname, pg_statio_all_indexes.idx_blks_read, pg_statio_all_indexes.idx_blks_hit FROM pg_statio_all_indexes WHERE (((pg_statio_all_indexes.schemaname <> 'pg_catalog'::name) AND (pg_statio_all_indexes.schemaname <> 'pg_toast'::name)) AND (pg_statio_all_indexes.schemaname <> 'information_schema'::name));
  pg_statio_user_sequences | SELECT pg_statio_all_sequences.relid, pg_statio_all_sequences.schemaname, pg_statio_all_sequences.relname, pg_statio_all_sequences.blks_read, pg_statio_all_sequences.blks_hit FROM pg_statio_all_sequences WHERE (((pg_statio_all_sequences.schemaname <> 'pg_catalog'::name) AND (pg_statio_all_sequences.schemaname <> 'pg_toast'::name)) AND (pg_statio_all_sequences.schemaname <> 'information_schema'::name));
  pg_statio_user_tables    | SELECT pg_statio_all_tables.relid, pg_statio_all_tables.schemaname, pg_statio_all_tables.relname, pg_statio_all_tables.heap_blks_read, pg_statio_all_tables.heap_blks_hit, pg_statio_all_tables.idx_blks_read, pg_statio_all_tables.idx_blks_hit, pg_statio_all_tables.toast_blks_read, pg_statio_all_tables.toast_blks_hit, pg_statio_all_tables.tidx_blks_read, pg_statio_all_tables.tidx_blks_hit FROM pg_statio_all_tables WHERE (((pg_statio_all_tables.schemaname <> 'pg_catalog'::name) AND (pg_statio_all_tables.schemaname <> 'pg_toast'::name)) AND (pg_statio_all_tables.schemaname <> 'information_schema'::name));
- pg_stats                 | SELECT nspname AS schemaname, relname AS tablename, attname, stanullfrac AS null_frac, stawidth AS avg_width, stadistinct AS n_distinct, CASE 1 WHEN stakind1 THEN stavalues1 WHEN stakind2 THEN stavalues2 WHEN stakind3 THEN stavalues3 WHEN stakind4 THEN stavalues4 ELSE NULL::"unknown" END AS most_common_vals, CASE 1 WHEN stakind1 THEN stanumbers1 WHEN stakind2 THEN stanumbers2 WHEN stakind3 THEN stanumbers3 WHEN stakind4 THEN stanumbers4 ELSE NULL::real[] END AS most_common_freqs, CASE 2 WHEN stakind1 THEN stavalues1 WHEN stakind2 THEN stavalues2 WHEN stakind3 THEN stavalues3 WHEN stakind4 THEN stavalues4 ELSE NULL::"unknown" END AS histogram_bounds, CASE 3 WHEN stakind1 THEN stanumbers1[1] WHEN stakind2 THEN stanumbers2[1] WHEN stakind3 THEN stanumbers3[1] WHEN stakind4 THEN stanumbers4[1] ELSE NULL::real END AS correlation FROM (((pg_statistic s JOIN pg_class c ON ((c.oid = s.starelid))) JOIN pg_attribute a ON (((c.oid = a.attrelid) AND (a.attnum = s.staattnum)))) LEFT JOIN pg_namespace n ON ((n.oid = c.relnamespace))) WHERE has_table_privilege(c.oid, 'select'::text);
+ pg_stats                 | SELECT n.nspname AS schemaname, c.relname AS tablename, a.attname, s.stanullfrac AS null_frac, s.stawidth AS avg_width, s.stadistinct AS n_distinct, CASE 1 WHEN s.stakind1 THEN s.stavalues1 WHEN s.stakind2 THEN s.stavalues2 WHEN s.stakind3 THEN s.stavalues3 WHEN s.stakind4 THEN s.stavalues4 ELSE NULL::"unknown" END AS most_common_vals, CASE 1 WHEN s.stakind1 THEN s.stanumbers1 WHEN s.stakind2 THEN s.stanumbers2 WHEN s.stakind3 THEN s.stanumbers3 WHEN s.stakind4 THEN s.stanumbers4 ELSE NULL::real[] END AS most_common_freqs, CASE 2 WHEN s.stakind1 THEN s.stavalues1 WHEN s.stakind2 THEN s.stavalues2 WHEN s.stakind3 THEN s.stavalues3 WHEN s.stakind4 THEN s.stavalues4 ELSE NULL::"unknown" END AS histogram_bounds, CASE 3 WHEN s.stakind1 THEN s.stanumbers1[1] WHEN s.stakind2 THEN s.stanumbers2[1] WHEN s.stakind3 THEN s.stanumbers3[1] WHEN s.stakind4 THEN s.stanumbers4[1] ELSE NULL::real END AS correlation FROM (((pg_statistic s JOIN pg_class c ON ((c.oid = s.starelid))) JOIN pg_attribute a ON (((c.oid = a.attrelid) AND (a.attnum = s.staattnum)))) LEFT JOIN pg_namespace n ON ((n.oid = c.relnamespace))) WHERE has_table_privilege(c.oid, 'select'::text);
  pg_tables                | SELECT n.nspname AS schemaname, c.relname AS tablename, pg_get_userbyid(c.relowner) AS tableowner, t.spcname AS "tablespace", c.relhasindex AS hasindexes, c.relhasrules AS hasrules, (c.reltriggers > 0) AS hastriggers FROM ((pg_class c LEFT JOIN pg_namespace n ON ((n.oid = c.relnamespace))) LEFT JOIN pg_tablespace t ON ((t.oid = c.reltablespace))) WHERE (c.relkind = 'r'::"char");
  pg_user                  | SELECT pg_shadow.usename, pg_shadow.usesysid, pg_shadow.usecreatedb, pg_shadow.usesuper, pg_shadow.usecatupd, '********'::text AS passwd, pg_shadow.valuntil, pg_shadow.useconfig FROM pg_shadow;
  pg_views                 | SELECT n.nspname AS schemaname, c.relname AS viewname, pg_get_userbyid(c.relowner) AS viewowner, pg_get_viewdef(c.oid) AS definition FROM (pg_class c LEFT JOIN pg_namespace n ON ((n.oid = c.relnamespace))) WHERE (c.relkind = 'v'::"char");