title: Great Expectations - Run Validation over specific subset of a PostgreSQL table
body: <p>I am fairly new to Great Expectations - and have a question. Essentially I have a PostgreSQL database, and every time I run my data pipeline, i want to validate a specific subset of the PostgreSQL table based off some key. Eg: If the data pipeline is run every day, the would be a field called current_batch. And the validation would occur for the below query:</p>
  <p>SELECT * FROM jobs WHERE current_batch = &lt;input_batch&gt;.</p>
  <p>I am unsure the best way to complete this. I am a using v3-api of great expectations and am a bit confused as to whether to use a checkpoint, or a validator. I assume I want to use a checkpoint but I can't seem to figure out how to create a checkpoint, but then only validate a specific subset of the PostgreSQL datasource.</p>
  <p>Any help or guidance would be much appreciated.</p>
  <p>Thanks,</p>