How to filter by query string in google analytics?

@virginie 

To filter by query string in Google Analytics, follow these steps:

1. Sign in to your Google Analytics account.
2. Go to the "Admin" section by clicking on the gear icon at the bottom left corner.
3. In the "View" column, click on "Filters".
4. Click on the "+ Add Filter" button to create a new filter.
5. Enter a name for the filter to easily identify it.
6. Select the "Custom" filter type.
7. Under the "Filter Field" dropdown, select "Query Parameter".
8. Enter the query parameter value you want to filter by. For example, if you want to filter all URLs with a specific query parameter "source", enter "source" in the "Filter Pattern" field.
9. Choose whether you want to include or exclude the matching URLs.
10. Click on the "Verify this filter" link to check how many URLs will be affected by the filter.
11. Once you're satisfied, click on the "Save" button to apply the filter.

Google Analytics will now filter and display only the URLs that match your specified query parameter.