Allows to connect to databases on a remote PostgreSQL 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.
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:
```
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: