> ## Documentation Index
> Fetch the complete documentation index at: https://docs.risingwave.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Query PostgreSQL tables (non-CDC)

> Fetch data from PostgreSQL tables on demand via the postgres_query table-valued function (non-CDC).

RisingWave allows you to query PostgreSQL tables directly with the `postgres_query` table-valued function (TVF). It offers a simpler alternative to Change Data Capture (CDC) when working with PostgreSQL data in RisingWave.

Unlike CDC, which continuously syncs data changes, this function lets you fetch data directly from PostgreSQL when needed. Therefore, this approach is ideal for static or infrequently updated data, as it's more resource-efficient than maintaining a constant CDC connection.

<Note>
  **Not CDC.** This approach fetches rows on demand via a table-valued function. For continuous change replication, use [PostgreSQL CDC](/ingestion/sources/postgresql/pg-cdc).
</Note>

## Syntax

Define `postgres_query` in either of the following forms:

```sql theme={null}
postgres_query(
    hostname varchar,      -- Database hostname
    port varchar,          -- Database port
    username varchar,      -- Authentication username
    password varchar,      -- Authentication password
    database_name varchar, -- Target database name
    query varchar          -- SQL query to execute
)
```

```sql theme={null}
postgres_query(
    cdc_source_name varchar, -- Existing PostgreSQL CDC source name
    query varchar            -- SQL query to execute
)
```

The source-based form requires an existing [PostgreSQL CDC](/ingestion/sources/postgresql/pg-cdc) source. It reuses the connection properties already defined on that source, including credentials managed as secrets.

## Example

1. In your PostgreSQL database, create a table and populate it with sample data.

```sql theme={null}
CREATE TABLE test (id bigint primary key, x int);
INSERT INTO test SELECT id, id::int FROM generate_series(1, 100) AS t(id);
```

2. In RisingWave, use `postgres_query` function to retrieve rows where `id > 90`.

```sql theme={null}
SELECT * 
FROM postgres_query('localhost', '5432', 'postgres', 'postgres', 'mydb', 'SELECT * FROM test WHERE id > 90;');
----RESULT
91 91
92 92
93 93
94 94
95 95
96 96
97 97
98 98
99 99
100 100
```

If you already have a PostgreSQL CDC source, you can reuse its connection properties instead of passing them inline again.

```sql theme={null}
CREATE SOURCE pg_source WITH (
    connector = 'postgres-cdc',
    hostname = 'postgres',
    port = '5432',
    username = 'myuser',
    password = secret pg_password,
    database.name = 'mydb',
    schema.name = 'public'
);

SELECT *
FROM postgres_query(
    'pg_source',
    'SELECT * FROM test WHERE id > 90;'
);
```