How does Partition Expression work in OpenMetadata?

[abuberkut]

Hello
Our team has started writing tests in OpenMetadata but doesn’t fully understand what Partition Expression is and where it should be used.

@TeddyCr

Questions:

1. How does OM use Partition Expression?

• Is it a filter for the SQL test or only for calculating Passed/Failed Row Count?
• How does it interact with Compute Row Count when enabled?

2. Where and how can it be used?

• Can it be used for time slices, categories, groups, or window functions?
• Are there syntax restrictions depending on the database dialect?

3. Which metrics does Partition Expression affect?

• How does OM calculate Passed/Failed Rows and percentages?

Goal: to understand the real functionality of Partition Expression, when it should be used, and what its limitations are.

[abuberkut]

Does anyone know about this parameter?

[TeddyCr]

@abuberkut as mentioned in the tool tip, this expression will be use to compute the pass / fail row count.

[abuberkut]

@abuberkut as mentioned in the tool tip, this expression will be use to compute the pass / fail row count.

Hi
Thanks for your response
I just want to understand the use cases where this parameter would be needed.

Example

Main SQL query:
SELECT *
FROM table
WHERE category IS NULL

Results in DB (not a test):

• Total rows in table: 902000
• Rows with category IS NULL: 2000

Result in OpenMetadata Test without Partition Expression

• Status: Failed
• Result Row Count: 2000
• Passed Rows: 900000
• Failed Rows: 2000
• Passed Rows %: 99.78%
• Failed Rows %: 0.22%

Result with Partition Expression

Partition Expression: _cdc_tsms >= '2025-09-01'

• In DB for the period:

• Total: 7505

• Errors: 5

• Successful rows: 7500

• In OpenMetadata:

• Status: Failed

• Result Row Count (error rows): 2000

• Passed Rows (by Partition Expression − Failed Rows): 5505

• Failed Rows: 2000

• Passed Rows %: 26.64%

• Failed Rows %: 73.36%

⚠️ The difference with the database results occurs because OM Result Row Count takes SQL rows, while Partition Expression is used only for Calculating Passed/Failed metrics.

I'm not sure where I'd need such metrics. Maybe you know.
If you have any examples, I'd be happy to hear them.

[abuberkut]

I know how it works, but I don't know where to use it

[abuberkut]

@TeddyCr