Sort search result by sku

I have variant products, sku is only set for variant. For example I have product named “T-shirt”, variant size L SKU-shirtL, variant size M SKU -shirtM

Then I search by product name “shirt”, I can see prevsious product in list. but if I sort result by SKU, then the variant product is gone. Because product itself does not have SKU, only variant has SKU set.