3.4 KiB
| toc_priority | toc_title |
|---|---|
| 8 | PostgreSQL |
PosgtreSQL
The PostgreSQL engine allows you to perform SELECT queries on data that is stored on a remote PostgreSQL server.
Creating a Table
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 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 values to the ClickHouse 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.
Usage Example
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)
Table in ClickHouse, retrieving data from the PostgreSQL table created above:
CREATE TABLE default.postgresql_table
(
`float_nullable` Nullable(Float32),
`str` String,
`int_id` Int32
)
ENGINE = PostgreSQL('localhost:5432', 'public', 'test', 'postges_user', 'postgres_password');
SELECT * FROM postgresql_table WHERE str IN ('test')
┌─float_nullable─┬─str──┬─int_id─┐
│ ᴺᵁᴸᴸ │ test │ 1 │
└────────────────┴──────┴────────┘
1 rows in set. Elapsed: 0.019 sec.