在SQL Server索引中包含列

Question

所有非聚集索引（NCI）還將存儲聚集索引（CI）的鍵列

在創建NCI時，如果我們有意地將鍵列包括在內，將會發生什么情況，那么占用空間又一次嗎？

表示存儲密鑰列，將占用兩次空間嗎？

提前致謝

Answer 1

不，空間不會占用兩次。

create table test (id int not null primary key, c1 int, c2 int)

create index ix1_test on test (c1)
create index ix2_test on test (c1) include (id)
create index ix3_test on test (c1) include (id, c2)

sp_SQLskills_SQL2012_helpindex顯示此信息：

index_name  index_description     index_keys    included_columns    columns_in_tree columns_in_leaf
[PK__test]  clustered, unique, PK [id]        NULL                  [id]            All columns "included"
[ix1_test]  nonclustered          [c1]        NULL                  [c1], [id]      [c1], [id]
[ix2_test]  nonclustered          [c1]        [id]                  [c1], [id]      [c1], [id]
[ix3_test]  nonclustered          [c1]        [id], [c2]            [c1], [id]      [c1], [id], [c2]