In working with Sanity and GROQ, there might be instances where you need to filter data using an optional field, and want a default value to kick in when null values are returned. For instance, consider an __i18n field added after a significant amount of content was already created. In this scenario, there's a batch of content that lacks a set value. In such a case, we'd prefer to use "en" as the fallback.
This requirement can be elegantly addressed using the coalesce function directly within the filter. By doing so, we can default the __i18n field to "en" using a more straightforward and compact syntax: coalesce(__i18n, "en"). This function greatly simplifies the query, making your code cleaner and more efficient.