ClickHouse/docs/en/engines/database-engines/postgresql.md
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2021-03-14 20:11:26 +03:00

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---
toc_priority: 35
toc_title: PostgreSQL
---
# PostgreSQL {#postgresql}
Allows to connect to databases on a remote [PostgreSQL](https://www.postgresql.org) server. Supports read and write operations (`SELECT` and `INSERT` queries) to exchange data between ClickHouse and PostgreSQL.
Gives the real-time access to table list and table structure from remote PostgreSQL with the help of `SHOW TABLES` and `DESCRIBE TABLE` queries.
Supports table structure modifications (`ALTER TABLE ... ADD|DROP COLUMN`). If `use_table_cache` parameter (see the Engine Parameters below) it set to `1`, the table structure is cached and not checked for being modified, but can be updated with `DETACH` and `ATTACH` queries.
## Creating a Database {#creating-a-database}
``` sql
CREATE DATABASE test_database
ENGINE = PostgreSQL('host:port', 'database', 'user', 'password'[, `use_table_cache`]);
```
**Engine Parameters**
- `host:port` — PostgreSQL server address.
- `database` — Remote database name.
- `user` — PostgreSQL user.
- `password` — User password.
- `use_table_cache` — Defines if the database table structure is cached or not. Optional. Default value: `0`.
## Data Types Support {#data_types-support}
| PostgerSQL | ClickHouse |
|------------------|--------------------------------------------------------------|
| DATE | [Date](../../sql-reference/data-types/date.md) |
| TIMESTAMP | [DateTime](../../sql-reference/data-types/datetime.md) |
| REAL | [Float32](../../sql-reference/data-types/float.md) |
| DOUBLE | [Float64](../../sql-reference/data-types/float.md) |
| DECIMAL, NUMERIC | [Decimal](../../sql-reference/data-types/decimal.md) |
| SMALLINT | [Int16](../../sql-reference/data-types/int-uint.md) |
| INTEGER | [Int32](../../sql-reference/data-types/int-uint.md) |
| BIGINT | [Int64](../../sql-reference/data-types/int-uint.md) |
| SERIAL | [UInt32](../../sql-reference/data-types/int-uint.md) |
| BIGSERIAL | [UInt64](../../sql-reference/data-types/int-uint.md) |
| TEXT, CHAR | [String](../../sql-reference/data-types/string.md) |
| INTEGER | Nullable([Int32](../../sql-reference/data-types/int-uint.md))|
| ARRAY | [Array](../../sql-reference/data-types/array.md) |
## Examples of Use {#examples-of-use}
Database in ClickHouse, exchanging data with the PostgreSQL server:
``` sql
CREATE DATABASE test_database
ENGINE = PostgreSQL('postgres1:5432', 'test_database', 'postgres', 'mysecretpassword', 1);
```
``` sql
SHOW DATABASES;
```
``` text
┌─name──────────┐
│ default │
│ test_database │
│ system │
└───────────────┘
```
``` sql
SHOW TABLES FROM test_database;
```
``` text
┌─name───────┐
│ test_table │
└────────────┘
```
Reading data from the PostgreSQL table:
``` sql
SELECT * FROM test_database.test_table;
```
``` text
┌─id─┬─value─┐
│ 1 │ 2 │
└────┴───────┘
```
Writing data to the PostgreSQL table:
``` sql
INSERT INTO test_database.test_table VALUES (3,4);
SELECT * FROM test_database.test_table;
```
``` text
┌─int_id─┬─value─┐
│ 1 │ 2 │
│ 3 │ 4 │
└────────┴───────┘
```
Consider the table structure was modified in PostgreSQL:
``` sql
postgre> ALTER TABLE test_table ADD COLUMN data Text
```
As the `use_table_cache` parameter was set to `1` when the database was created, the table structure in ClickHouse was cached and therefore not modified:
``` sql
DESCRIBE TABLE test_database.test_table;
```
``` text
┌─name───┬─type──────────────┐
│ id │ Nullable(Integer) │
│ value │ Nullable(Integer) │
└────────┴───────────────────┘
```
After detaching the table and attaching it again, the structure was updated:
``` sql
DETACH TABLE test_database.test_table;
ATTACH TABLE test_database.test_table;
DESCRIBE TABLE test_database.test_table;
```
``` text
┌─name───┬─type──────────────┐
│ id │ Nullable(Integer) │
│ value │ Nullable(Integer) │
│ data │ Nullable(String) │
└────────┴───────────────────┘
```
[Original article](https://clickhouse.tech/docs/en/database-engines/postgresql/) <!--hide-->