Replace slow UNION ALL query with optimized all_objects query in describe

Replace the 4-way UNION ALL query across all_tables, all_views, and
all_synonyms with a single all_objects query for the common TABLE/VIEW
path. Synonym targets are resolved via a second all_synonyms query only
when needed.

- Add ORDER BY to preserve lookup priority (table, view, owner synonym,
  public synonym)
- Add regression test covering table, view, private synonym and public
  synonym resolution for the same underlying table
- Grant CREATE/DROP PUBLIC SYNONYM to test users

Refs #2429

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: yahonda

lib/active_record/connection_adapters/oracle_enhanced/connection.rb

@@ -34,30 +34,26 @@ def describe(name)
               table_owner, table_name = default_owner, real_name
             end
             sql = <<~SQL.squish
-              SELECT owner, table_name, 'TABLE' name_type
-              FROM all_tables
-              WHERE owner = :table_owner
-                AND table_name = :table_name
-              UNION ALL
-              SELECT owner, view_name table_name, 'VIEW' name_type
-              FROM all_views
-              WHERE owner = :table_owner
-                AND view_name = :table_name
-              UNION ALL
-              SELECT table_owner, table_name, 'SYNONYM' name_type
-              FROM all_synonyms
-              WHERE owner = :table_owner
-                AND synonym_name = :table_name
-              UNION ALL
-              SELECT table_owner, table_name, 'SYNONYM' name_type
-              FROM all_synonyms
-              WHERE owner = 'PUBLIC'
-                AND synonym_name = :real_name
+              SELECT owner, object_name table_name, object_type name_type
+              FROM all_objects
+              WHERE ((owner = :table_owner AND object_name = :table_name)
+                 OR (owner = 'PUBLIC' AND object_name = :real_name))
+                AND object_type IN ('TABLE', 'VIEW', 'SYNONYM')
+              ORDER BY DECODE(owner, 'PUBLIC', 2, 1),
+                       DECODE(object_type, 'TABLE', 1, 'VIEW', 2, 'SYNONYM', 3)
             SQL
-            if result = _select_one(sql, "CONNECTION", [table_owner, table_name, table_owner, table_name, table_owner, table_name, real_name])
+            if result = _select_one(sql, "CONNECTION", [table_owner, table_name, real_name])
               case result["name_type"]
               when "SYNONYM"
-                describe("#{result['owner'] && "#{result['owner']}."}#{result['table_name']}")
+                synonym_sql = <<~SQL.squish
+                  SELECT table_owner, table_name
+                  FROM all_synonyms
+                  WHERE owner = :owner
+                    AND synonym_name = :synonym_name
+                SQL
+                if syn = _select_one(synonym_sql, "CONNECTION", [result["owner"], result["table_name"]])
+                  describe("#{syn['table_owner'] && "#{syn['table_owner']}."}#{syn['table_name']}")
+                end
               else
                 [result["owner"], result["table_name"]]
               end

spec/active_record/connection_adapters/oracle_enhanced/connection_spec.rb

@@ -577,6 +577,23 @@ def kill_current_session
       expect(@conn.describe("all_tables")).to eq(["SYS", "ALL_TABLES"])
     end
 
+    it "should describe table, view, private synonym and public synonym for the same underlying table" do
+      @conn.exec "CREATE TABLE test_describe_all (id NUMBER)" rescue nil
+      @conn.exec "CREATE VIEW test_describe_all_v AS SELECT * FROM test_describe_all" rescue nil
+      @conn.exec "CREATE SYNONYM test_describe_all_syn FOR test_describe_all" rescue nil
+      @conn.exec "CREATE PUBLIC SYNONYM test_describe_all_pub FOR #{@owner}.test_describe_all" rescue nil
+
+      expect(@conn.describe("test_describe_all")).to eq([@owner, "TEST_DESCRIBE_ALL"])
+      expect(@conn.describe("test_describe_all_v")).to eq([@owner, "TEST_DESCRIBE_ALL_V"])
+      expect(@conn.describe("test_describe_all_syn")).to eq([@owner, "TEST_DESCRIBE_ALL"])
+      expect(@conn.describe("test_describe_all_pub")).to eq([@owner, "TEST_DESCRIBE_ALL"])
+    ensure
+      @conn.exec "DROP PUBLIC SYNONYM test_describe_all_pub" rescue nil
+      @conn.exec "DROP SYNONYM test_describe_all_syn" rescue nil
+      @conn.exec "DROP VIEW test_describe_all_v" rescue nil
+      @conn.exec "DROP TABLE test_describe_all" rescue nil
+    end
+
     if defined?(OCI8)
       context "OCI8 adapter" do
         it "should not fallback to SELECT-based logic when querying non-existent table information" do

spec/support/create_oracle_enhanced_users.sql

@@ -4,10 +4,12 @@ CREATE USER oracle_enhanced IDENTIFIED BY oracle_enhanced;
 
 GRANT unlimited tablespace, create session, create table, create sequence,
 create procedure, create trigger, create view, create materialized view,
-create database link, create synonym, create type, ctxapp TO oracle_enhanced;
+create database link, create synonym, create public synonym, create type, ctxapp TO oracle_enhanced;
+GRANT drop public synonym TO oracle_enhanced;
 
 CREATE USER oracle_enhanced_schema IDENTIFIED BY oracle_enhanced_schema;
 
 GRANT unlimited tablespace, create session, create table, create sequence,
 create procedure, create trigger, create view, create materialized view,
-create database link, create synonym, create type, ctxapp TO oracle_enhanced_schema;
+create database link, create synonym, create public synonym, create type, ctxapp TO oracle_enhanced_schema;
+GRANT drop public synonym TO oracle_enhanced_schema;