Allow setting the excluded columns directly.

README.md

@@ -248,10 +248,19 @@ a column would be in its own table, but if not then it can be excluded
 with an optional parameter:
 
 ``` sql
-SELECT periods.add_system_time_period('example',
+SELECT periods.add_system_time_period(
+            'example',
             excluded_column_names => ARRAY['foo', 'bar']);
 ```
 
+Excluded columns can be define after the fact, as well.
+
+``` sql
+SELECT periods.set_system_time_period_excluded_columns(
+            'example',
+            ARRAY['foo', 'bar']);
+```
+
 This functionality is not present in the SQL standard.
 
 ## `WITH SYSTEM VERSIONING`

expected/excluded_columns.out

@@ -84,6 +84,47 @@ SELECT value, null_value, flap, system_time_start <> :'now2' AS changed FROM exc
  howdy folks! |          0 | on   | t
 (1 row)
 
+/* Test directly setting the excluded columns */
+SELECT periods.drop_system_versioning('excl');
+ drop_system_versioning 
+------------------------
+ t
+(1 row)
+
+ALTER TABLE excl ADD COLUMN flop text;
+ALTER TABLE excl_history ADD COLUMN flop text;
+SELECT periods.add_system_versioning('excl');
+ add_system_versioning 
+-----------------------
+
+(1 row)
+
+SELECT periods.set_system_time_period_excluded_columns('excl', ARRAY['flap', 'flop']);
+ set_system_time_period_excluded_columns 
+-----------------------------------------
+
+(1 row)
+
+TABLE periods.system_time_periods;
+ table_name | period_name |      infinity_check_constraint      |     generated_always_trigger      |     write_history_trigger      | truncate_trigger | excluded_column_names 
+------------+-------------+-------------------------------------+-----------------------------------+--------------------------------+------------------+-----------------------
+ excl       | system_time | excl_system_time_end_infinity_check | excl_system_time_generated_always | excl_system_time_write_history | excl_truncate    | {flap,flop}
+(1 row)
+
+UPDATE excl SET flop = 'flop';
+SELECT value, null_value, flap, flop FROM excl;
+    value     | null_value | flap | flop 
+--------------+------------+------+------
+ howdy folks! |          0 | on   | flop
+(1 row)
+
+SELECT value, null_value, flap, flop FROM excl_history ORDER BY system_time_start;
+    value     | null_value | flap | flop 
+--------------+------------+------+------
+ hello world  |            | on   | 
+ howdy folks! |            | on   | 
+(2 rows)
+
 SELECT periods.drop_system_versioning('excl');
  drop_system_versioning 
 ------------------------

expected/excluded_columns_1.out

@@ -82,6 +82,47 @@ SELECT value, null_value, flap, system_time_start <> :'now2' AS changed FROM exc
  howdy folks! |          0 | on   | t
 (1 row)
 
+/* Test directly setting the excluded columns */
+SELECT periods.drop_system_versioning('excl');
+ drop_system_versioning 
+------------------------
+ t
+(1 row)
+
+ALTER TABLE excl ADD COLUMN flop text;
+ALTER TABLE excl_history ADD COLUMN flop text;
+SELECT periods.add_system_versioning('excl');
+ add_system_versioning 
+-----------------------
+
+(1 row)
+
+SELECT periods.set_system_time_period_excluded_columns('excl', ARRAY['flap', 'flop']);
+ set_system_time_period_excluded_columns 
+-----------------------------------------
+
+(1 row)
+
+TABLE periods.system_time_periods;
+ table_name | period_name |      infinity_check_constraint      |     generated_always_trigger      |     write_history_trigger      | truncate_trigger | excluded_column_names 
+------------+-------------+-------------------------------------+-----------------------------------+--------------------------------+------------------+-----------------------
+ excl       | system_time | excl_system_time_end_infinity_check | excl_system_time_generated_always | excl_system_time_write_history | excl_truncate    | {flap,flop}
+(1 row)
+
+UPDATE excl SET flop = 'flop';
+SELECT value, null_value, flap, flop FROM excl;
+    value     | null_value | flap | flop 
+--------------+------------+------+------
+ howdy folks! |          0 | on   | flop
+(1 row)
+
+SELECT value, null_value, flap, flop FROM excl_history ORDER BY system_time_start;
+    value     | null_value | flap | flop 
+--------------+------------+------+------
+ hello world  |            | on   | 
+ howdy folks! |            | on   | 
+(2 rows)
+
 SELECT periods.drop_system_versioning('excl');
  drop_system_versioning 
 ------------------------

periods--1.0--1.1.sql

@@ -922,3 +922,44 @@ BEGIN
 END;
 $function$;
 
+CREATE FUNCTION periods.set_system_time_period_excluded_columns(
+    table_name regclass,
+    excluded_column_names name[])
+ RETURNS void
+ LANGUAGE plpgsql
+AS
+$function$
+#variable_conflict use_variable
+DECLARE
+    excluded_column_name name;
+BEGIN
+    /* Always serialize operations on our catalogs */
+    PERFORM periods._serialize(table_name);
+
+    /* Make sure all the excluded columns exist */
+    FOR excluded_column_name IN
+        SELECT u.name
+        FROM unnest(excluded_column_names) AS u (name)
+        WHERE NOT EXISTS (
+            SELECT FROM pg_catalog.pg_attribute AS a
+            WHERE (a.attrelid, a.attname) = (table_name, u.name))
+    LOOP
+        RAISE EXCEPTION 'column "%" does not exist', excluded_column_name;
+    END LOOP;
+
+    /* Don't allow system columns to be excluded either */
+    FOR excluded_column_name IN
+        SELECT u.name
+        FROM unnest(excluded_column_names) AS u (name)
+        JOIN pg_catalog.pg_attribute AS a ON (a.attrelid, a.attname) = (table_name, u.name)
+        WHERE a.attnum < 0
+    LOOP
+        RAISE EXCEPTION 'cannot exclude system column "%"', excluded_column_name;
+    END LOOP;
+
+    /* Do it. */
+    UPDATE periods.system_time_periods AS stp SET
+        excluded_column_names = excluded_column_names
+    WHERE stp.table_name = table_name;
+END;
+$function$;

sql/excluded_columns.sql

@@ -36,6 +36,18 @@ SELECT value, null_value, flap, system_time_start <> :'now' AS changed FROM excl
 UPDATE excl SET null_value = 0;
 SELECT value, null_value, flap, system_time_start <> :'now2' AS changed FROM excl;
 
+/* Test directly setting the excluded columns */
+SELECT periods.drop_system_versioning('excl');
+ALTER TABLE excl ADD COLUMN flop text;
+ALTER TABLE excl_history ADD COLUMN flop text;
+SELECT periods.add_system_versioning('excl');
+
+SELECT periods.set_system_time_period_excluded_columns('excl', ARRAY['flap', 'flop']);
+TABLE periods.system_time_periods;
+UPDATE excl SET flop = 'flop';
+SELECT value, null_value, flap, flop FROM excl;
+SELECT value, null_value, flap, flop FROM excl_history ORDER BY system_time_start;
+
 SELECT periods.drop_system_versioning('excl');
 SELECT periods.drop_system_time_period('excl');
 DROP TABLE excl;