4.8 KiB
| sidebar_position | sidebar_label |
|---|---|
| 42 | postgresql |
postgresql
Allows SELECT and INSERT queries to be performed on data that is stored on a remote PostgreSQL server.
Syntax
postgresql('host:port', 'database', 'table', 'user', 'password'[, `schema`])
Arguments
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.
Returned Value
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.
:::
Implementation Details
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.
:::
Supports multiple replicas that must be listed by |. For example:
SELECT name FROM postgresql(`postgres{1|2|3}:5432`, 'postgres_database', 'postgres_table', 'user', 'password');
or
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.
Examples
Table in PostgreSQL:
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:
SELECT * FROM postgresql('localhost:5432', 'test', 'test', 'postgresql_user', 'password') WHERE str IN ('test');
┌─int_id─┬─int_nullable─┬─float─┬─str──┬─float_nullable─┐
│ 1 │ ᴺᵁᴸᴸ │ 2 │ test │ ᴺᵁᴸᴸ │
└────────┴──────────────┴───────┴──────┴────────────────┘
Inserting:
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');
┌─int_id─┬─int_nullable─┬─float─┬─str──┬─float_nullable─┐
│ 1 │ ᴺᵁᴸᴸ │ 2 │ test │ ᴺᵁᴸᴸ │
│ 2 │ ᴺᵁᴸᴸ │ 3 │ │ ᴺᵁᴸᴸ │
└────────┴──────────────┴───────┴──────┴────────────────┘
Using Non-default Schema:
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)
CREATE TABLE pg_table_schema_with_dots (a UInt32)
ENGINE PostgreSQL('localhost:5432', 'clickhouse', 'nice.table', 'postgrsql_user', 'password', 'nice.schema');
See Also