Best approach for querying by SKU in a product catalog using Sanity.io and GraphQL.

Based on the information about product catalog management in Sanity, I'd recommend adding SKU directly to your individual product documents rather than creating a separate document type. Here's why:

Direct SKU approach (recommended):

• Store the SKU field directly on each product document type
• Query by SKU using GROQ filters like *[_type == "product" && sku == "ABC123"][0]
• This is the standard pattern used in e-commerce implementations with Sanity

Why this works better:

1. Simpler queries: You can directly query any document type by SKU without needing to traverse references
2. Better performance: Direct field queries are faster than reference lookups
3. Easier maintenance: No need to keep separate SKU documents in sync
4. Flexibility: Each document type can have its own SKU while still being queryable

If you need to query across multiple document types:

You can use a GROQ query that searches multiple types at once:

*[_type in ["productType1", "productType2", "productType3"] && sku == $sku][0]

Or if you want to find all documents with a specific SKU regardless of type:

*[defined(sku) && sku == $sku]

When you might consider a separate SKU document:

The separate document approach only makes sense if:

• You need complex SKU-specific metadata that doesn't belong on product documents
• You're managing SKUs that can point to different product types over time
• You need a central registry for SKU allocation/validation

But for most product catalogs, the direct approach is cleaner and more maintainable. As mentioned in the structured content patterns for e-commerce guide, storing SKUs directly on product documents (often within variant arrays) is the standard pattern in e-commerce implementations.