---
toc_priority: 8
toc_title: PostgreSQL
---

# PosgtreSQL {#postgresql}

The PostgreSQL engine allows you to perform `SELECT` queries on data that is stored on a remote PostgreSQL server.

## Creating a Table {#creating-a-table}

``` sql
CREATE TABLE [IF NOT EXISTS] [db.]table_name [ON CLUSTER cluster]
(
    name1 [type1] [DEFAULT|MATERIALIZED|ALIAS expr1] [TTL expr1],
    name2 [type2] [DEFAULT|MATERIALIZED|ALIAS expr2] [TTL expr2],
    ...
) ENGINE = PostgreSQL('host:port', 'database', 'table', 'user', 'password');
```

See a detailed description of the [CREATE TABLE](../../../sql-reference/statements/create/table.md#create-table-query) query.

The table structure can differ from the original PostgreSQL table structure:

-   Column names should be the same as in the original PostgreSQL table, but you can use just some of these columns and in any order.
-   Column types may differ from those in the original PostgreSQL table. ClickHouse tries to [cast](../../../sql-reference/functions/type-conversion-functions.md#type_conversion_function-cast) values to the ClickHouse data types.
-   Setting `external_table_functions_use_nulls` defines how to handle Nullable columns. Default is 1, if 0 - table function will not make nullable columns and will insert default values instead of nulls. This is also applicable for null values inside array data types.

**Engine Parameters**

-   `host:port` — PostgreSQL server address.

-   `database` — Remote database name.

-   `table` — Remote table name.

-   `user` — PostgreSQL user.

-   `password` — User password.

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 `=, !=, >, >=, <, <=, 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.
Be careful in PostgreSQL an array data type column like Integer[] may contain arrays of different dimensions in different rows, but in ClickHouse only allows multidimensional arrays of the same dimension in all rows.

## Usage Example {#usage-example}

Table in PostgreSQL:

``` text
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)
```

Table in ClickHouse, retrieving data from the PostgreSQL table created above:

``` sql
CREATE TABLE default.postgresql_table
(
    `float_nullable` Nullable(Float32),
    `str` String,
    `int_id` Int32
)
ENGINE = PostgreSQL('localhost:5432', 'public', 'test', 'postges_user', 'postgres_password');
```

``` sql
SELECT * FROM postgresql_table WHERE str IN ('test') 
```

``` text
┌─float_nullable─┬─str──┬─int_id─┐
│           ᴺᵁᴸᴸ │ test │      1 │
└────────────────┴──────┴────────┘
1 rows in set. Elapsed: 0.019 sec.
```


## See Also {#see-also}

-   [The ‘postgresql’ table function](../../../sql-reference/table-functions/postgresql.md)
-   [Using PostgreSQL as a source of external dictionary](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-sources.md#dicts-external_dicts_dict_sources-postgresql)