Amazon Redshift will no longer support the creation of new Python UDFs starting Patch 198. Existing Python UDFs will continue to function until June 30, 2026. For more information, see the [ blog post ](https://aws.amazon.com/blogs/big-data/amazon-redshift-python-user-defined-functions-will-reach-end-of-support-after-june-30-2026/). 

# Example: Performing correlated subqueries in Redshift Spectrum
<a name="c_performing-correlated-subqueries-spectrum"></a>

This topic describes how to perform correlated subqueries in Redshift Spectrum. A correlated subquery is a query that uses values from the outer query.

You can perform correlated subqueries in Redshift Spectrum. The `$spectrum_oid` pseudocolumn provides the ability to perform correlated queries with Redshift Spectrum. To perform a correlated subquery, the pseudocolumn `$spectrum_oid` must be enabled but doesn't appear in the SQL statement. For more information, see [Pseudocolumns](c-spectrum-external-tables.md#c-spectrum-external-tables-pseudocolumns).

To create the external schema and external tables for this example, see [Getting started with Amazon Redshift Spectrum](c-getting-started-using-spectrum.md).

Following is an example of a correlated subquery in Redshift Spectrum. 

```
select *
from myspectrum_schema.sales s
where exists
( select *
from myspectrum_schema.listing l
where l.listid = s.listid )
order by salesid
limit 5;
```

```
salesid  listid   sellerid   buyerid   eventid   dateid  qtysold  pricepaid   commission   saletime
1        1        36861      21191     7872      1875    4        728         109.2        2008-02-18 02:36:48
2        4        8117       11498     4337      1983    2        76          11.4         2008-06-06 05:00:16	
3        5        1616       17433     8647      1983    2        350         52.5         2008-06-06 08:26:17	
4        5        1616       19715     8647      1986    1        175         26.25        2008-06-09 08:38:52	
5        6        47402      14115     8240      2069    2        154         23.1         2008-08-31 09:17:02
```