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103 lines
3.4 KiB
Markdown
103 lines
3.4 KiB
Markdown
---
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toc_priority: 8
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toc_title: PostgreSQL
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---
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# PosgtreSQL {#postgresql}
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The PostgreSQL engine allows you to perform `SELECT` queries on data that is stored on a remote PostgreSQL server.
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## Creating a Table {#creating-a-table}
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``` sql
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CREATE TABLE [IF NOT EXISTS] [db.]table_name [ON CLUSTER cluster]
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(
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name1 [type1] [DEFAULT|MATERIALIZED|ALIAS expr1] [TTL expr1],
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name2 [type2] [DEFAULT|MATERIALIZED|ALIAS expr2] [TTL expr2],
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...
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) ENGINE = PostgreSQL('host:port', 'database', 'table', 'user', 'password');
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```
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See a detailed description of the [CREATE TABLE](../../../sql-reference/statements/create/table.md#create-table-query) query.
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The table structure can differ from the original PostgreSQL table structure:
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- 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.
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- 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.
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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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- `table` — Remote table name.
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- `user` — PostgreSQL user.
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- `password` — User password.
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SELECT Queries on PostgreSQL side run as `COPY (SELECT ...) TO STDOUT` inside read-only PostgreSQL transaction with commit after each `SELECT` query.
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Simple `WHERE` clauses such as `=, !=, >, >=, <, <=, IN` are executed on the PostgreSQL server.
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All joins, aggregations, sorting, `IN [ array ]` conditions and the `LIMIT` sampling constraint are executed in ClickHouse only after the query to PostgreSQL finishes.
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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.
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PostgreSQL Array types converts into ClickHouse arrays.
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## Usage Example {#usage-example}
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Table in PostgreSQL:
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``` text
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postgres=# CREATE TABLE "public"."test" (
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"int_id" SERIAL,
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"int_nullable" INT NULL DEFAULT NULL,
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"float" FLOAT NOT NULL,
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"str" VARCHAR(100) NOT NULL DEFAULT '',
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"float_nullable" FLOAT NULL DEFAULT NULL,
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PRIMARY KEY (int_id));
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CREATE TABLE
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postgres=# insert into test (int_id, str, "float") VALUES (1,'test',2);
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INSERT 0 1
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postgresql> select * from test;
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int_id | int_nullable | float | str | float_nullable
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--------+--------------+-------+------+----------------
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1 | | 2 | test |
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(1 row)
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```
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Table in ClickHouse, retrieving data from the PostgreSQL table created above:
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``` sql
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CREATE TABLE default.postgresql_table
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(
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`float_nullable` Nullable(Float32),
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`str` String,
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`int_id` Int32
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)
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ENGINE = PostgreSQL('localhost:5432', 'public', 'test', 'postges_user', 'postgres_password');
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```
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``` sql
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SELECT * FROM postgresql_table WHERE str IN ('test')
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```
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``` text
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┌─float_nullable─┬─str──┬─int_id─┐
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│ ᴺᵁᴸᴸ │ test │ 1 │
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└────────────────┴──────┴────────┘
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1 rows in set. Elapsed: 0.019 sec.
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```
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## See Also {#see-also}
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- [The ‘postgresql’ table function](../../../sql-reference/table-functions/postgresql.md)
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- [Using PostgreSQL as a source of external dictionary](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-sources.md#dicts-external_dicts_dict_sources-postgresql)
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