Add missing indexes to duplicated columns

[kvch]

Previously, when an indexes column was duplicated, the index was lost during the duplication process. This PR adds the missing indexes to the duplicated columns.

The example I added removes NOT NULL constraint from a column that has a hash index with a custom fillfactor.

The schema of the table before starting the migration:

postgres=# \d fruits
                                          Table "public.fruits"
 Column |          Type          | Collation | Nullable |                    Default
--------+------------------------+-----------+----------+------------------------------------------------
 id     | integer                |           | not null | nextval('_pgroll_new_fruits_id_seq'::regclass)
 name   | character varying(255) |           | not null |
 size   | fruit_size             |           | not null | 'small'::fruit_size
Indexes:
    "_pgroll_new_fruits_pkey" PRIMARY KEY, btree (id) REPLICA IDENTITY
    "_pgroll_new_fruits_name_key" UNIQUE CONSTRAINT, btree (name)
    "idx_fruits_id_gt_10" btree (id) WHERE id > 10
    "idx_fruits_name" hash (name) WITH (fillfactor='70')
    "idx_fruits_unique_name" UNIQUE, btree (name)

Without the fix in my PR starting the example migration is incorrect. Notice that the duplicated column _pgroll_new_name is does not have a hash index:

postgres=# \d fruits
                                               Table "public.fruits"
      Column      |          Type          | Collation | Nullable |                    Default
------------------+------------------------+-----------+----------+------------------------------------------------
 id               | integer                |           | not null | nextval('_pgroll_new_fruits_id_seq'::regclass)
 name             | character varying(255) |           | not null |
 size             | fruit_size             |           | not null | 'small'::fruit_size
 _pgroll_new_name | character varying(255) |           |          |
Indexes:
    "_pgroll_new_fruits_pkey" PRIMARY KEY, btree (id) REPLICA IDENTITY
    "_pgroll_dup__pgroll_new_fruits_name_key" UNIQUE, btree (_pgroll_new_name)
    "_pgroll_new_fruits_name_key" UNIQUE CONSTRAINT, btree (name)
    "idx_fruits_id_gt_10" btree (id) WHERE id > 10
    "idx_fruits_name" hash (name) WITH (fillfactor='70')
    "idx_fruits_unique_name" UNIQUE, btree (name)
Triggers:
    _pgroll_trigger_fruits__pgroll_new_name BEFORE INSERT OR UPDATE ON fruits FOR EACH ROW EXECUTE FUNCTION _pgroll_trigger_fruits__pgroll_new_name()
    _pgroll_trigger_fruits_name BEFORE INSERT OR UPDATE ON fruits FOR EACH ROW EXECUTE FUNCTION _pgroll_trigger_fruits_name()

After completing the migration the hash index on name disappears:

postgres=# \d fruits
                                          Table "public.fruits"
 Column |          Type          | Collation | Nullable |                    Default
--------+------------------------+-----------+----------+------------------------------------------------
 id     | integer                |           | not null | nextval('_pgroll_new_fruits_id_seq'::regclass)
 size   | fruit_size             |           | not null | 'small'::fruit_size
 name   | character varying(255) |           |          |
Indexes:
    "_pgroll_new_fruits_pkey" PRIMARY KEY, btree (id) REPLICA IDENTITY
    "_pgroll_new_fruits_name_key" UNIQUE CONSTRAINT, btree (name)
    "idx_fruits_id_gt_10" btree (id) WHERE id > 10

With my change starting the migration creates the missing hash index on the duplicated column. See _pgroll_dup_idx_fruits_name index on _pgroll_new_name:

postgres=# \d fruits
                                               Table "public.fruits"
      Column      |          Type          | Collation | Nullable |                    Default
------------------+------------------------+-----------+----------+------------------------------------------------
 id               | integer                |           | not null | nextval('_pgroll_new_fruits_id_seq'::regclass)
 name             | character varying(255) |           | not null |
 size             | fruit_size             |           | not null | 'small'::fruit_size
 _pgroll_new_name | character varying(255) |           |          |
Indexes:
    "_pgroll_new_fruits_pkey" PRIMARY KEY, btree (id) REPLICA IDENTITY
    "_pgroll_dup__pgroll_new_fruits_name_key" UNIQUE, btree (_pgroll_new_name)
    "_pgroll_dup_idx_fruits_name" hash (_pgroll_new_name) WITH (fillfactor='70')
    "_pgroll_dup_idx_fruits_unique_name" UNIQUE, btree (_pgroll_new_name)
    "_pgroll_new_fruits_name_key" UNIQUE CONSTRAINT, btree (name)
    "idx_fruits_id_gt_10" btree (id) WHERE id > 10
    "idx_fruits_name" hash (name) WITH (fillfactor='70')
    "idx_fruits_unique_name" UNIQUE, btree (name)
Triggers:
    _pgroll_trigger_fruits__pgroll_new_name BEFORE INSERT OR UPDATE ON fruits FOR EACH ROW EXECUTE FUNCTION _pgroll_trigger_fruits__pgroll_new_name()
    _pgroll_trigger_fruits_name BEFORE INSERT OR UPDATE ON fruits FOR EACH ROW EXECUTE FUNCTION _pgroll_trigger_fruits_name()

Completing the migration preserves the index on name and removes the NOT NULL constraint:

postgres=# \d fruits
                                          Table "public.fruits"
 Column |          Type          | Collation | Nullable |                    Default
--------+------------------------+-----------+----------+------------------------------------------------
 id     | integer                |           | not null | nextval('_pgroll_new_fruits_id_seq'::regclass)
 size   | fruit_size             |           | not null | 'small'::fruit_size
 name   | character varying(255) |           |          |
Indexes:
    "_pgroll_new_fruits_pkey" PRIMARY KEY, btree (id) REPLICA IDENTITY
    "_pgroll_new_fruits_name_key" UNIQUE CONSTRAINT, btree (name)
    "idx_fruits_id_gt_10" btree (id) WHERE id > 10
    "idx_fruits_name" hash (name) WITH (fillfactor='70')
    "idx_fruits_unique_name" UNIQUE CONSTRAINT, btree (name)

Related to #227

[andrew-farries]

This looks good 👍

I left some minor comments and one potential problem about how pgroll will now convert unique indexes on duplicated columns into unique constraints.