PostgreSQL

31.4. Column Lists
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31.4. Column Lists

Each publication can optionally specify which columns of each table are replicated to subscribers. The table on the subscriber side must have at least all the columns that are published. If no column list is specified, then all columns on the publisher are replicated. See CREATE PUBLICATION for details on the syntax.

The choice of columns can be based on behavioral or performance reasons. However, do not rely on this feature for security: a malicious subscriber is able to obtain data from columns that are not specifically published. If security is a consideration, protections can be applied at the publisher side.

If no column list is specified, any columns added later are automatically replicated. This means that having a column list which names all columns is not the same as having no column list at all.

A column list can contain only simple column references. The order of columns in the list is not preserved.

Specifying a column list when the publication also publishes FOR TABLES IN SCHEMA is not supported.

For partitioned tables, the publication parameter publish_via_partition_root determines which column list is used. If publish_via_partition_root is true, the root partitioned table’s column list is used. Otherwise, if publish_via_partition_root is false (the default), each partition’s column list is used.

If a publication publishes UPDATE or DELETE operations, any column list must include the table’s replica identity columns (see REPLICA IDENTITY). If a publication publishes only INSERT operations, then the column list may omit replica identity columns.

Column lists have no effect for the TRUNCATE command.

During initial data synchronization, only the published columns are copied. However, if the subscriber is from a release prior to 15, then all the columns in the table are copied during initial data synchronization, ignoring any column lists.

== Warning: Combining Column Lists from Multiple Publications

There’s currently no support for subscriptions comprising several publications where the same table has been published with different column lists. CREATE SUBSCRIPTION disallows creating such subscriptions, but it is still possible to get into that situation by adding or altering column lists on the publication side after a subscription has been created.

This means changing the column lists of tables on publications that are already subscribed could lead to errors being thrown on the subscriber side.

If a subscription is affected by this problem, the only way to resume replication is to adjust one of the column lists on the publication side so that they all match; and then either recreate the subscription, or use ALTER SUBSCRIPTION ... DROP PUBLICATION to remove one of the offending publications and add it again.

31.4.1. Examples

Create a table t1 to be used in the following example.

test_pub=# CREATE TABLE t1(id int, a text, b text, c text, d text, e text, PRIMARY KEY(id));
CREATE TABLE

Create a publication p1. A column list is defined for table t1 to reduce the number of columns that will be replicated. Notice that the order of column names in the column list does not matter.

test_pub=# CREATE PUBLICATION p1 FOR TABLE t1 (id, b, a, d);
CREATE PUBLICATION

psql can be used to show the column lists (if defined) for each publication.

test_pub=# \dRp+
                               Publication p1
  Owner   | All tables | Inserts | Updates | Deletes | Truncates | Via root
----------+------------+---------+---------+---------+-----------+----------
 postgres | f          | t       | t       | t       | t         | f
Tables:
    "public.t1" (id, a, b, d)

psql can be used to show the column lists (if defined) for each table.

test_pub=# \d t1
                 Table "public.t1"
 Column |  Type   | Collation | Nullable | Default
--------+---------+-----------+----------+---------
 id     | integer |           | not null |
 a      | text    |           |          |
 b      | text    |           |          |
 c      | text    |           |          |
 d      | text    |           |          |
 e      | text    |           |          |
Indexes:
    "t1_pkey" PRIMARY KEY, btree (id)
Publications:
    "p1" (id, a, b, d)

On the subscriber node, create a table t1 which now only needs a subset of the columns that were on the publisher table t1, and also create the subscription s1 that subscribes to the publication p1.

test_sub=# CREATE TABLE t1(id int, b text, a text, d text, PRIMARY KEY(id));
CREATE TABLE
test_sub=# CREATE SUBSCRIPTION s1
test_sub-# CONNECTION 'host=localhost dbname=test_pub application_name=s1'
test_sub-# PUBLICATION p1;
CREATE SUBSCRIPTION

On the publisher node, insert some rows to table t1.

test_pub=# INSERT INTO t1 VALUES(1, 'a-1', 'b-1', 'c-1', 'd-1', 'e-1');
INSERT 0 1
test_pub=# INSERT INTO t1 VALUES(2, 'a-2', 'b-2', 'c-2', 'd-2', 'e-2');
INSERT 0 1
test_pub=# INSERT INTO t1 VALUES(3, 'a-3', 'b-3', 'c-3', 'd-3', 'e-3');
INSERT 0 1
test_pub=# SELECT * FROM t1 ORDER BY id;
 id |  a  |  b  |  c  |  d  |  e
----+-----+-----+-----+-----+-----
  1 | a-1 | b-1 | c-1 | d-1 | e-1
  2 | a-2 | b-2 | c-2 | d-2 | e-2
  3 | a-3 | b-3 | c-3 | d-3 | e-3
(3 rows)

Only data from the column list of publication p1 is replicated.

test_sub=# SELECT * FROM t1 ORDER BY id;
 id |  b  |  a  |  d
----+-----+-----+-----
  1 | b-1 | a-1 | d-1
  2 | b-2 | a-2 | d-2
  3 | b-3 | a-3 | d-3
(3 rows)

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