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> Allows `SELECT` and `INSERT` queries to be performed on data that is stored on a remote PostgreSQL server.

# postgresql

Allows `SELECT` and `INSERT` queries to be performed on data that is stored on a remote PostgreSQL server.

<h2 id="syntax">
  Syntax
</h2>

```sql theme={null}
postgresql({host:port, database, table, user, password[, schema, [, on_conflict]] | named_collection[, option=value [,..]]})
```

<h2 id="arguments">
  Arguments
</h2>

| Argument      | Description                                                                |
| ------------- | -------------------------------------------------------------------------- |
| `host:port`   | PostgreSQL server address.                                                 |
| `database`    | Remote database name.                                                      |
| `table`       | Remote table name.                                                         |
| `user`        | PostgreSQL user.                                                           |
| `password`    | User password.                                                             |
| `schema`      | Non-default table schema. Optional.                                        |
| `on_conflict` | Conflict resolution strategy. Example: `ON CONFLICT DO NOTHING`. Optional. |

Arguments also can be passed using [named collections](/concepts/features/configuration/server-config/named-collections). In this case `host` and `port` should be specified separately. This approach is recommended for production environment.

<h2 id="returned_value">
  Returned value
</h2>

A table object with the same columns as the original PostgreSQL table.

<Note>
  In the `INSERT` query to distinguish table function `postgresql(...)` from table name with column names list you must use keywords `FUNCTION` or `TABLE FUNCTION`. See examples below.
</Note>

<h2 id="implementation-details">
  Implementation Details
</h2>

`SELECT` queries on PostgreSQL side run as `COPY (SELECT ...) TO STDOUT` inside read-only PostgreSQL transaction with commit after each `SELECT` query.

Simple `WHERE` clauses such as `=`, `!=`, `>`, `>=`, `<`, `<=`, and `IN` are executed on the PostgreSQL server.

All joins, aggregations, sorting, `IN [ array ]` conditions and the `LIMIT` sampling constraint are executed in ClickHouse only after the query to PostgreSQL finishes.

`INSERT` queries on PostgreSQL side run as `COPY "table_name" (field1, field2, ... fieldN) FROM STDIN` inside PostgreSQL transaction with auto-commit after each `INSERT` statement.

PostgreSQL Array types converts into ClickHouse arrays.

<Note>
  Be careful, in PostgreSQL an array data type column like Integer\[] may contain arrays of different dimensions in different rows, but in ClickHouse it is only allowed to have multidimensional arrays of the same dimension in all rows.
</Note>

Supports multiple replicas that must be listed by `|`. For example:

```sql theme={null}
SELECT name FROM postgresql(`postgres{1|2|3}:5432`, 'postgres_database', 'postgres_table', 'user', 'password');
```

or

```sql theme={null}
SELECT name FROM postgresql(`postgres1:5431|postgres2:5432`, 'postgres_database', 'postgres_table', 'user', 'password');
```

Supports replicas priority for PostgreSQL dictionary source. The bigger the number in map, the less the priority. The highest priority is `0`.

<h2 id="examples">
  Examples
</h2>

Table in PostgreSQL:

```text theme={null}
postgres=# CREATE TABLE "public"."test" (
"int_id" SERIAL,
"int_nullable" INT NULL DEFAULT NULL,
"float" FLOAT NOT NULL,
"str" VARCHAR(100) NOT NULL DEFAULT '',
"float_nullable" FLOAT NULL DEFAULT NULL,
PRIMARY KEY (int_id));

CREATE TABLE

postgres=# INSERT INTO test (int_id, str, "float") VALUES (1,'test',2);
INSERT 0 1

postgresql> SELECT * FROM test;
  int_id | int_nullable | float | str  | float_nullable
 --------+--------------+-------+------+----------------
       1 |              |     2 | test |
(1 row)
```

Selecting data from ClickHouse using plain arguments:

```sql theme={null}
SELECT * FROM postgresql('localhost:5432', 'test', 'test', 'postgresql_user', 'password') WHERE str IN ('test');
```

Or using [named collections](/concepts/features/configuration/server-config/named-collections):

```sql theme={null}
CREATE NAMED COLLECTION mypg AS
        host = 'localhost',
        port = 5432,
        database = 'test',
        user = 'postgresql_user',
        password = 'password';
SELECT * FROM postgresql(mypg, table='test') WHERE str IN ('test');
```

```text theme={null}
┌─int_id─┬─int_nullable─┬─float─┬─str──┬─float_nullable─┐
│      1 │         ᴺᵁᴸᴸ │     2 │ test │           ᴺᵁᴸᴸ │
└────────┴──────────────┴───────┴──────┴────────────────┘
```

Inserting:

```sql theme={null}
INSERT INTO TABLE FUNCTION postgresql('localhost:5432', 'test', 'test', 'postgrsql_user', 'password') (int_id, float) VALUES (2, 3);
SELECT * FROM postgresql('localhost:5432', 'test', 'test', 'postgresql_user', 'password');
```

```text theme={null}
┌─int_id─┬─int_nullable─┬─float─┬─str──┬─float_nullable─┐
│      1 │         ᴺᵁᴸᴸ │     2 │ test │           ᴺᵁᴸᴸ │
│      2 │         ᴺᵁᴸᴸ │     3 │      │           ᴺᵁᴸᴸ │
└────────┴──────────────┴───────┴──────┴────────────────┘
```

Using Non-default Schema:

```text theme={null}
postgres=# CREATE SCHEMA "nice.schema";

postgres=# CREATE TABLE "nice.schema"."nice.table" (a integer);

postgres=# INSERT INTO "nice.schema"."nice.table" SELECT i FROM generate_series(0, 99) as t(i)
```

```sql theme={null}
CREATE TABLE pg_table_schema_with_dots (a UInt32)
        ENGINE PostgreSQL('localhost:5432', 'clickhouse', 'nice.table', 'postgrsql_user', 'password', 'nice.schema');
```

<h2 id="related">
  Related
</h2>

* [The PostgreSQL table engine](/reference/engines/table-engines/integrations/postgresql)
* [Using PostgreSQL as a dictionary source](/reference/statements/create/dictionary/sources/postgresql)

<h3 id="replicating-or-migrating-postgres-data-with-peerdb">
  Replicating or migrating Postgres data with PeerDB
</h3>

> In addition to table functions, you can always use [PeerDB](https://docs.peerdb.io/introduction) by ClickHouse to set up a continuous data pipeline from Postgres to ClickHouse. PeerDB is a tool designed specifically to replicate data from Postgres to ClickHouse using change data capture (CDC).