Use a query that's compatible with PostgreSQL 9.2

Also, explicitly apply the order: generate_subscripts is unlikely to
start returning values out of order, but we should still be clear about
what we want.

1 files changed, 11 insertions, 7 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
index 1d439acb07..02a6da2f71 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
@@ -344,13 +344,17 @@ module ActiveRecord
 
         def primary_keys(table_name) # :nodoc:
           select_values(<<-SQL.strip_heredoc, "SCHEMA")
-            SELECT a.attname FROM pg_index i
-            CROSS JOIN generate_subscripts(i.indkey, 1) k
-             JOIN pg_attribute a
-               ON a.attrelid = i.indrelid
-              AND a.attnum = i.indkey[k]
-            WHERE i.indrelid = #{quote(quote_table_name(table_name))}::regclass
-              AND i.indisprimary
+            SELECT a.attname
+              FROM (
+                     SELECT indrelid, indkey, generate_subscripts(indkey, 1) idx
+                       FROM pg_index
+                      WHERE indrelid = #{quote(quote_table_name(table_name))}::regclass
+                        AND indisprimary
+                   ) i
+              JOIN pg_attribute a
+                ON a.attrelid = i.indrelid
+               AND a.attnum = i.indkey[i.idx]
+             ORDER BY i.idx
           SQL
         end