I have observed that for a query when the PK is in select list and if we create a NC index with column in where clause and add PK as include column this improves performance from NC index seek and keyloopup to new non clustered index seek .My doubt is when we create a Non clustered index the clustering key is already a part of it and then why adding PK column as included help change the execution plan to a better performance. Please correct me if I am wrong.
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