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140 lines
4.7 KiB
Markdown
140 lines
4.7 KiB
Markdown
---
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slug: /en/engines/database-engines/postgresql
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sidebar_position: 40
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sidebar_label: PostgreSQL
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---
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# PostgreSQL
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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.
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Gives the real-time access to table list and table structure from remote PostgreSQL with the help of `SHOW TABLES` and `DESCRIBE TABLE` queries.
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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.
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## Creating a Database {#creating-a-database}
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``` sql
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CREATE DATABASE test_database
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ENGINE = PostgreSQL('host:port', 'database', 'user', 'password'[, `schema`, `use_table_cache`]);
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```
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**Engine Parameters**
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- `host:port` — PostgreSQL server address.
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- `database` — Remote database name.
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- `user` — PostgreSQL user.
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- `password` — User password.
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- `schema` — PostgreSQL schema.
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- `use_table_cache` — Defines if the database table structure is cached or not. Optional. Default value: `0`.
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## Data Types Support {#data_types-support}
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| PostgreSQL | ClickHouse |
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|------------------|--------------------------------------------------------------|
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| DATE | [Date](../../sql-reference/data-types/date.md) |
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| TIMESTAMP | [DateTime](../../sql-reference/data-types/datetime.md) |
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| REAL | [Float32](../../sql-reference/data-types/float.md) |
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| DOUBLE | [Float64](../../sql-reference/data-types/float.md) |
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| DECIMAL, NUMERIC | [Decimal](../../sql-reference/data-types/decimal.md) |
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| SMALLINT | [Int16](../../sql-reference/data-types/int-uint.md) |
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| INTEGER | [Int32](../../sql-reference/data-types/int-uint.md) |
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| BIGINT | [Int64](../../sql-reference/data-types/int-uint.md) |
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| SERIAL | [UInt32](../../sql-reference/data-types/int-uint.md) |
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| BIGSERIAL | [UInt64](../../sql-reference/data-types/int-uint.md) |
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| TEXT, CHAR | [String](../../sql-reference/data-types/string.md) |
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| INTEGER | Nullable([Int32](../../sql-reference/data-types/int-uint.md))|
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| ARRAY | [Array](../../sql-reference/data-types/array.md) |
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## Examples of Use {#examples-of-use}
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Database in ClickHouse, exchanging data with the PostgreSQL server:
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``` sql
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CREATE DATABASE test_database
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ENGINE = PostgreSQL('postgres1:5432', 'test_database', 'postgres', 'mysecretpassword', 'schema_name',1);
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```
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``` sql
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SHOW DATABASES;
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```
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``` text
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┌─name──────────┐
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│ default │
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│ test_database │
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│ system │
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└───────────────┘
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```
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``` sql
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SHOW TABLES FROM test_database;
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```
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``` text
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┌─name───────┐
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│ test_table │
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└────────────┘
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```
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Reading data from the PostgreSQL table:
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``` sql
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SELECT * FROM test_database.test_table;
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```
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``` text
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┌─id─┬─value─┐
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│ 1 │ 2 │
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└────┴───────┘
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```
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Writing data to the PostgreSQL table:
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``` sql
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INSERT INTO test_database.test_table VALUES (3,4);
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SELECT * FROM test_database.test_table;
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```
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``` text
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┌─int_id─┬─value─┐
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│ 1 │ 2 │
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│ 3 │ 4 │
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└────────┴───────┘
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```
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Consider the table structure was modified in PostgreSQL:
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``` sql
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postgre> ALTER TABLE test_table ADD COLUMN data Text
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```
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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:
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``` sql
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DESCRIBE TABLE test_database.test_table;
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```
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``` text
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┌─name───┬─type──────────────┐
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│ id │ Nullable(Integer) │
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│ value │ Nullable(Integer) │
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└────────┴───────────────────┘
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```
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After detaching the table and attaching it again, the structure was updated:
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``` sql
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DETACH TABLE test_database.test_table;
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ATTACH TABLE test_database.test_table;
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DESCRIBE TABLE test_database.test_table;
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```
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``` text
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┌─name───┬─type──────────────┐
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│ id │ Nullable(Integer) │
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│ value │ Nullable(Integer) │
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│ data │ Nullable(String) │
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└────────┴───────────────────┘
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```
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