Not : Clustered vs Non-clustered indexes yazısına bakabilirsiniz.
Açıklaması şöyle. CREATE INDEX ile yaratılan index non-clustered ve içinde veri taşımıyor. Sadece clustered index'e pointer gibi.
Normal İşleyiş
Açıklaması şöyle
When querying using a non-clustered index, the database performs an index seek to first locate the index key and the clustered index.
If the requested data is not in the non-clustered index tree, the database performs a key lookup in the clustered index tree to retrieve the entire row and join the data.
This key lookup incurs additional I/O and can slow down the query.
INCLUDE
Açıklaması şöyle
When querying using a non-clustered index, the database performs an index seek to first locate the index key and the clustered index.
If the requested data is not in the non-clustered index tree, the database performs a key lookup in the clustered index tree to retrieve the entire row and join the data.
This key lookup incurs additional I/O and can slow down the query.
To mitigate this issue, you can use the INCLUDE command to include non-key columns in the non-clustered index tree.
Örnek
Şöyle yaparız
CREATE INDEX idx_example ON employee_tab (name) INCLUDE (age);
Hiç yorum yok:
Yorum Gönder