Add support for excluded columns.

These are columns for which updates do not cause `GENERATED ALWAYS AS
ROW START` to change, and historical rows will not be generated.

This is not in the standard, but was requested by several people.

CHANGELOG.md

@@ -6,6 +6,12 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 ## [Unreleased]
 
+  - Add support for excluded columns. These are columns for which
+    updates do not cause `GENERATED ALWAYS AS ROW START` to change, and
+    historical rows will not be generated.
+
+    This is not in the standard, but was requested by several people.
+
 ## [1.0] – 2019-08-25
 
 ### Added

Makefile

@@ -9,6 +9,7 @@ REGRESS = install \
 		  periods \
 		  system_time_periods \
 		  system_versioning \
+		  excluded_columns \
 		  unique_foreign \
 		  for_portion_of \
 		  predicates \

README.md

@@ -238,6 +238,22 @@ created both by the SQL standard and by this extension. A special
 function is provided as a convenience, but `add_period` can also be
 called.
 
+### Excluding columns
+
+It might be desirable to prevent some columns from updating the
+`SYSTEM_TIME` values. For example, perhaps your `users` table has a
+column `last_login` which gets updated all the time and you don’t want
+to generate a new historical row (see below) for just that. Ideally such
+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',
+            excluded_column_names => ARRAY['foo', 'bar']);
+```
+
+This functionality is not present in the SQL standard.
+
 ## `WITH SYSTEM VERSIONING`
 
 This special `SYSTEM_TIME` period can be used to keep track of changes

expected/drop_protection.out

@@ -10,7 +10,8 @@ CREATE TYPE integerrange AS RANGE (SUBTYPE = integer);
 CREATE TABLE dp (
     id bigint,
     s integer,
-    e integer
+    e integer,
+    x boolean
 );
 /* periods */
 SELECT periods.add_period('dp', 'p', 's', 'e', 'integerrange');
@@ -23,12 +24,15 @@ DROP TYPE integerrange;
 ERROR:  cannot drop rangetype "public.integerrange" because it is used in period "p" on table "dp"
 CONTEXT:  PL/pgSQL function periods.drop_protection() line 56 at RAISE
 /* system_time_periods */
-SELECT periods.add_system_time_period('dp');
+SELECT periods.add_system_time_period('dp', excluded_column_names => ARRAY['x']);
  add_system_time_period 
 ------------------------
  t
 (1 row)
 
+ALTER TABLE dp DROP COLUMN x; -- fails
+ERROR:  cannot drop or rename column "x" on table "dp" because it is excluded from SYSTEM VERSIONING
+CONTEXT:  PL/pgSQL function periods.drop_protection() line 124 at RAISE
 ALTER TABLE dp DROP CONSTRAINT dp_system_time_end_infinity_check; -- fails
 ERROR:  cannot drop constraint "dp_system_time_end_infinity_check" on table "dp" because it is used in SYSTEM_TIME period
 CONTEXT:  PL/pgSQL function periods.drop_protection() line 72 at RAISE
@@ -51,13 +55,13 @@ SELECT periods.add_for_portion_view('dp', 'p');
 
 DROP VIEW dp__for_portion_of_p;
 ERROR:  cannot drop view "public.dp__for_portion_of_p", call "periods.drop_for_portion_view()" instead
-CONTEXT:  PL/pgSQL function periods.drop_protection() line 125 at RAISE
+CONTEXT:  PL/pgSQL function periods.drop_protection() line 141 at RAISE
 DROP TRIGGER for_portion_of_p ON dp__for_portion_of_p;
 ERROR:  cannot drop trigger "for_portion_of_p" on view "dp__for_portion_of_p" because it is used in FOR PORTION OF view for period "p" on table "dp"
-CONTEXT:  PL/pgSQL function periods.drop_protection() line 137 at RAISE
+CONTEXT:  PL/pgSQL function periods.drop_protection() line 153 at RAISE
 ALTER TABLE dp DROP CONSTRAINT dp_pkey;
 ERROR:  cannot drop primary key on table "dp" because it has a FOR PORTION OF view for period "p"
-CONTEXT:  PL/pgSQL function periods.drop_protection() line 149 at RAISE
+CONTEXT:  PL/pgSQL function periods.drop_protection() line 165 at RAISE
 SELECT periods.drop_for_portion_view('dp', 'p');
  drop_for_portion_view 
 -----------------------
@@ -77,10 +81,10 @@ SELECT periods.add_unique_key('dp', ARRAY['id'], 'p', 'k', 'u', 'x');
 
 ALTER TABLE dp DROP CONSTRAINT u; -- fails
 ERROR:  cannot drop constraint "u" on table "dp" because it is used in period unique key "k"
-CONTEXT:  PL/pgSQL function periods.drop_protection() line 170 at RAISE
+CONTEXT:  PL/pgSQL function periods.drop_protection() line 186 at RAISE
 ALTER TABLE dp DROP CONSTRAINT x; -- fails
 ERROR:  cannot drop constraint "x" on table "dp" because it is used in period unique key "k"
-CONTEXT:  PL/pgSQL function periods.drop_protection() line 181 at RAISE
+CONTEXT:  PL/pgSQL function periods.drop_protection() line 197 at RAISE
 ALTER TABLE dp DROP CONSTRAINT dp_p_check; -- fails
 /* foreign_keys */
 CREATE TABLE dp_ref (LIKE dp);
@@ -98,16 +102,16 @@ SELECT periods.add_foreign_key('dp_ref', ARRAY['id'], 'p', 'k', key_name => 'f')
 
 DROP TRIGGER f_fk_insert ON dp_ref; -- fails
 ERROR:  cannot drop trigger "f_fk_insert" on table "dp_ref" because it is used in period foreign key "f"
-CONTEXT:  PL/pgSQL function periods.drop_protection() line 197 at RAISE
+CONTEXT:  PL/pgSQL function periods.drop_protection() line 213 at RAISE
 DROP TRIGGER f_fk_update ON dp_ref; -- fails
 ERROR:  cannot drop trigger "f_fk_update" on table "dp_ref" because it is used in period foreign key "f"
-CONTEXT:  PL/pgSQL function periods.drop_protection() line 208 at RAISE
+CONTEXT:  PL/pgSQL function periods.drop_protection() line 224 at RAISE
 DROP TRIGGER f_uk_update ON dp; -- fails
 ERROR:  cannot drop trigger "f_uk_update" on table "dp" because it is used in period foreign key "f"
-CONTEXT:  PL/pgSQL function periods.drop_protection() line 220 at RAISE
+CONTEXT:  PL/pgSQL function periods.drop_protection() line 236 at RAISE
 DROP TRIGGER f_uk_delete ON dp; -- fails
 ERROR:  cannot drop trigger "f_uk_delete" on table "dp" because it is used in period foreign key "f"
-CONTEXT:  PL/pgSQL function periods.drop_protection() line 232 at RAISE
+CONTEXT:  PL/pgSQL function periods.drop_protection() line 248 at RAISE
 SELECT periods.drop_foreign_key('dp_ref', 'f');
  drop_foreign_key 
 ------------------
@@ -133,27 +137,27 @@ drop cascades to function dp__between(timestamp with time zone,timestamp with ti
 drop cascades to function dp__between_symmetric(timestamp with time zone,timestamp with time zone)
 drop cascades to function dp__from_to(timestamp with time zone,timestamp with time zone)
 ERROR:  cannot drop table "public.dp_history" because it is used in SYSTEM VERSIONING for table "dp"
-CONTEXT:  PL/pgSQL function periods.drop_protection() line 248 at RAISE
+CONTEXT:  PL/pgSQL function periods.drop_protection() line 264 at RAISE
 DROP VIEW dp_with_history CASCADE;
 NOTICE:  drop cascades to 4 other objects
 DETAIL:  drop cascades to function dp__as_of(timestamp with time zone)
 drop cascades to function dp__between(timestamp with time zone,timestamp with time zone)
 drop cascades to function dp__between_symmetric(timestamp with time zone,timestamp with time zone)
 drop cascades to function dp__from_to(timestamp with time zone,timestamp with time zone)
 ERROR:  cannot drop view "public.dp_with_history" because it is used in SYSTEM VERSIONING for table "dp"
-CONTEXT:  PL/pgSQL function periods.drop_protection() line 260 at RAISE
+CONTEXT:  PL/pgSQL function periods.drop_protection() line 276 at RAISE
 DROP FUNCTION dp__as_of(timestamp with time zone);
 ERROR:  cannot drop function "public.dp__as_of(timestamp with time zone)" because it is used in SYSTEM VERSIONING for table "dp"
-CONTEXT:  PL/pgSQL function periods.drop_protection() line 272 at RAISE
+CONTEXT:  PL/pgSQL function periods.drop_protection() line 288 at RAISE
 DROP FUNCTION dp__between(timestamp with time zone,timestamp with time zone);
 ERROR:  cannot drop function "public.dp__between(timestamp with time zone,timestamp with time zone)" because it is used in SYSTEM VERSIONING for table "dp"
-CONTEXT:  PL/pgSQL function periods.drop_protection() line 272 at RAISE
+CONTEXT:  PL/pgSQL function periods.drop_protection() line 288 at RAISE
 DROP FUNCTION dp__between_symmetric(timestamp with time zone,timestamp with time zone);
 ERROR:  cannot drop function "public.dp__between_symmetric(timestamp with time zone,timestamp with time zone)" because it is used in SYSTEM VERSIONING for table "dp"
-CONTEXT:  PL/pgSQL function periods.drop_protection() line 272 at RAISE
+CONTEXT:  PL/pgSQL function periods.drop_protection() line 288 at RAISE
 DROP FUNCTION dp__from_to(timestamp with time zone,timestamp with time zone);
 ERROR:  cannot drop function "public.dp__from_to(timestamp with time zone,timestamp with time zone)" because it is used in SYSTEM VERSIONING for table "dp"
-CONTEXT:  PL/pgSQL function periods.drop_protection() line 272 at RAISE
+CONTEXT:  PL/pgSQL function periods.drop_protection() line 288 at RAISE
 SELECT periods.drop_system_versioning('dp', purge => true);
  drop_system_versioning 
 ------------------------

expected/drop_protection_1.out

@@ -10,7 +10,8 @@ CREATE TYPE integerrange AS RANGE (SUBTYPE = integer);
 CREATE TABLE dp (
     id bigint,
     s integer,
-    e integer
+    e integer,
+    x boolean
 );
 /* periods */
 SELECT periods.add_period('dp', 'p', 's', 'e', 'integerrange');
@@ -22,12 +23,14 @@ SELECT periods.add_period('dp', 'p', 's', 'e', 'integerrange');
 DROP TYPE integerrange;
 ERROR:  cannot drop rangetype "public.integerrange" because it is used in period "p" on table "dp"
 /* system_time_periods */
-SELECT periods.add_system_time_period('dp');
+SELECT periods.add_system_time_period('dp', excluded_column_names => ARRAY['x']);
  add_system_time_period 
 ------------------------
  t
 (1 row)
 
+ALTER TABLE dp DROP COLUMN x; -- fails
+ERROR:  cannot drop or rename column "x" on table "dp" because it is excluded from SYSTEM VERSIONING
 ALTER TABLE dp DROP CONSTRAINT dp_system_time_end_infinity_check; -- fails
 ERROR:  cannot drop constraint "dp_system_time_end_infinity_check" on table "dp" because it is used in SYSTEM_TIME period
 DROP TRIGGER dp_system_time_generated_always ON dp; -- fails

expected/excluded_columns.out

@@ -0,0 +1,86 @@
+CREATE TABLE excl (
+    value text NOT NULL,
+    null_value integer,
+    flap text NOT NULL
+);
+SELECT periods.add_system_time_period('excl', excluded_column_names => ARRAY['flap']);
+ add_system_time_period 
+------------------------
+ t
+(1 row)
+
+SELECT periods.add_system_versioning('excl');
+NOTICE:  history table "excl_history" created for "excl", be sure to index it properly
+ add_system_versioning 
+-----------------------
+
+(1 row)
+
+TABLE periods.periods;
+ table_name | period_name | start_column_name | end_column_name | range_type | bounds_check_constraint 
+------------+-------------+-------------------+-----------------+------------+-------------------------
+ excl       | system_time | system_time_start | system_time_end | tstzrange  | excl_system_time_check
+(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}
+(1 row)
+
+TABLE periods.system_versioning;
+ table_name | period_name | history_table_name |     view_name     |              func_as_of               |                           func_between                           |                           func_between_symmetric                           |                           func_from_to                           
+------------+-------------+--------------------+-------------------+---------------------------------------+------------------------------------------------------------------+----------------------------------------------------------------------------+------------------------------------------------------------------
+ excl       | system_time | excl_history       | excl_with_history | excl__as_of(timestamp with time zone) | excl__between(timestamp with time zone,timestamp with time zone) | excl__between_symmetric(timestamp with time zone,timestamp with time zone) | excl__from_to(timestamp with time zone,timestamp with time zone)
+(1 row)
+
+BEGIN;
+SELECT CURRENT_TIMESTAMP AS now \gset
+INSERT INTO excl (value, flap) VALUES ('hello world', 'off');
+COMMIT;
+SELECT value, null_value, flap, system_time_start <> :'now' AS changed FROM excl;
+    value    | null_value | flap | changed 
+-------------+------------+------+---------
+ hello world |            | off  | f
+(1 row)
+
+UPDATE excl SET flap = 'off';
+UPDATE excl SET flap = 'on';
+UPDATE excl SET flap = 'off';
+UPDATE excl SET flap = 'on';
+SELECT value, null_value, flap, system_time_start <> :'now' AS changed FROM excl;
+    value    | null_value | flap | changed 
+-------------+------------+------+---------
+ hello world |            | on   | f
+(1 row)
+
+BEGIN;
+SELECT CURRENT_TIMESTAMP AS now2 \gset
+UPDATE excl SET value = 'howdy folks!';
+COMMIT;
+SELECT value, null_value, flap, system_time_start <> :'now' AS changed FROM excl;
+    value     | null_value | flap | changed 
+--------------+------------+------+---------
+ howdy folks! |            | on   | t
+(1 row)
+
+UPDATE excl SET null_value = 0;
+SELECT value, null_value, flap, system_time_start <> :'now2' AS changed FROM excl;
+    value     | null_value | flap | changed 
+--------------+------------+------+---------
+ howdy folks! |          0 | on   | t
+(1 row)
+
+SELECT periods.drop_system_versioning('excl');
+ drop_system_versioning 
+------------------------
+ t
+(1 row)
+
+SELECT periods.drop_system_time_period('excl');
+ drop_system_time_period 
+-------------------------
+ t
+(1 row)
+
+DROP TABLE excl;

expected/health_checks.out

@@ -12,7 +12,7 @@ ERROR:  table "log" must be persistent
 CONTEXT:  PL/pgSQL function periods.add_period(regclass,name,name,name,regtype,name) line 72 at RAISE
 SELECT periods.add_system_time_period('log'); -- fails
 ERROR:  table "log" must be persistent
-CONTEXT:  PL/pgSQL function periods.add_system_time_period(regclass,name,name,name,name,name,name,name) line 72 at RAISE
+CONTEXT:  PL/pgSQL function periods.add_system_time_period(regclass,name,name,name,name,name,name,name,name[]) line 72 at RAISE
 ALTER TABLE log SET LOGGED;
 SELECT periods.add_period('log', 'p', 's', 'e'); -- passes
  add_period 

expected/rename_following.out

@@ -53,26 +53,29 @@ TABLE periods.periods;
 (1 row)
 
 /* system_time_periods */
-SELECT periods.add_system_time_period('rename_test');
+SELECT periods.add_system_time_period('rename_test', excluded_column_names => ARRAY['col3']);
  add_system_time_period 
 ------------------------
  t
 (1 row)
 
 TABLE periods.system_time_periods;
- table_name  | period_name |         infinity_check_constraint          |         generated_always_trigger         |         write_history_trigger         |   truncate_trigger   
--------------+-------------+--------------------------------------------+------------------------------------------+---------------------------------------+----------------------
- rename_test | system_time | rename_test_system_time_end_infinity_check | rename_test_system_time_generated_always | rename_test_system_time_write_history | rename_test_truncate
+ table_name  | period_name |         infinity_check_constraint          |         generated_always_trigger         |         write_history_trigger         |   truncate_trigger   | excluded_column_names 
+-------------+-------------+--------------------------------------------+------------------------------------------+---------------------------------------+----------------------+-----------------------
+ rename_test | system_time | rename_test_system_time_end_infinity_check | rename_test_system_time_generated_always | rename_test_system_time_write_history | rename_test_truncate | {col3}
 (1 row)
 
+ALTER TABLE rename_test RENAME col3 TO "COLUMN3";
+ERROR:  cannot drop or rename column "col3" on table "rename_test" because it is excluded from SYSTEM VERSIONING
+CONTEXT:  PL/pgSQL function periods.rename_following() line 121 at RAISE
 ALTER TABLE rename_test RENAME CONSTRAINT rename_test_system_time_end_infinity_check TO inf_check;
 ALTER TRIGGER rename_test_system_time_generated_always ON rename_test RENAME TO generated_always;
 ALTER TRIGGER rename_test_system_time_write_history ON rename_test RENAME TO write_history;
 ALTER TRIGGER rename_test_truncate ON rename_test RENAME TO trunc;
 TABLE periods.system_time_periods;
- table_name  | period_name | infinity_check_constraint | generated_always_trigger | write_history_trigger | truncate_trigger 
--------------+-------------+---------------------------+--------------------------+-----------------------+------------------
- rename_test | system_time | inf_check                 | generated_always         | write_history         | trunc
+ table_name  | period_name | infinity_check_constraint | generated_always_trigger | write_history_trigger | truncate_trigger | excluded_column_names 
+-------------+-------------+---------------------------+--------------------------+-----------------------+------------------+-----------------------
+ rename_test | system_time | inf_check                 | generated_always         | write_history         | trunc            | {col3}
 (1 row)
 
 /* for_portion_views */
@@ -147,19 +150,19 @@ TABLE periods.foreign_keys;
 
 ALTER TABLE rename_test_ref RENAME COLUMN "COLUMN1" TO col1; -- fails
 ERROR:  cannot drop or rename column "COLUMN1" on table "rename_test_ref" because it is used in period foreign key "rename_test_ref_col2_COLUMN1_col3_q"
-CONTEXT:  PL/pgSQL function periods.rename_following() line 194 at RAISE
+CONTEXT:  PL/pgSQL function periods.rename_following() line 210 at RAISE
 ALTER TRIGGER "rename_test_ref_col2_COLUMN1_col3_q_fk_insert" ON rename_test_ref RENAME TO fk_insert;
 ERROR:  cannot drop or rename trigger "rename_test_ref_col2_COLUMN1_col3_q_fk_insert" on table "rename_test_ref" because it is used in period foreign key "rename_test_ref_col2_COLUMN1_col3_q"
-CONTEXT:  PL/pgSQL function periods.rename_following() line 229 at RAISE
+CONTEXT:  PL/pgSQL function periods.rename_following() line 245 at RAISE
 ALTER TRIGGER "rename_test_ref_col2_COLUMN1_col3_q_fk_update" ON rename_test_ref RENAME TO fk_update;
 ERROR:  cannot drop or rename trigger "rename_test_ref_col2_COLUMN1_col3_q_fk_update" on table "rename_test_ref" because it is used in period foreign key "rename_test_ref_col2_COLUMN1_col3_q"
-CONTEXT:  PL/pgSQL function periods.rename_following() line 229 at RAISE
+CONTEXT:  PL/pgSQL function periods.rename_following() line 245 at RAISE
 ALTER TRIGGER "rename_test_ref_col2_COLUMN1_col3_q_uk_update" ON rename_test RENAME TO uk_update;
 ERROR:  cannot drop or rename trigger "rename_test_ref_col2_COLUMN1_col3_q_uk_update" on table "rename_test" because it is used in period foreign key "rename_test_ref_col2_COLUMN1_col3_q"
-CONTEXT:  PL/pgSQL function periods.rename_following() line 229 at RAISE
+CONTEXT:  PL/pgSQL function periods.rename_following() line 245 at RAISE
 ALTER TRIGGER "rename_test_ref_col2_COLUMN1_col3_q_uk_delete" ON rename_test RENAME TO uk_delete;
 ERROR:  cannot drop or rename trigger "rename_test_ref_col2_COLUMN1_col3_q_uk_delete" on table "rename_test" because it is used in period foreign key "rename_test_ref_col2_COLUMN1_col3_q"
-CONTEXT:  PL/pgSQL function periods.rename_following() line 229 at RAISE
+CONTEXT:  PL/pgSQL function periods.rename_following() line 245 at RAISE
 TABLE periods.foreign_keys;
               key_name               |   table_name    |    column_names     | period_name |          unique_key          | match_type | delete_action | update_action |               fk_insert_trigger               |               fk_update_trigger               |               uk_update_trigger               |               uk_delete_trigger               
 -------------------------------------+-----------------+---------------------+-------------+------------------------------+------------+---------------+---------------+-----------------------------------------------+-----------------------------------------------+-----------------------------------------------+-----------------------------------------------