select ColumnC from YourTable where ColumnnA = 12

另一方面,索引2要小得多,因此可以在内存中读取需要索引扫描的查询：

select * from YourTable where ColumnnA like '%hello%'

所以他们并不是多余的.

如果您不相信我的上述论点,您可以找到“冗余”索引,例如：

;with ind as (
    select  a.object_id,a.index_id,cast(col_list.list as varchar(max)) as list
    from    (
            select  distinct object_id,index_id
            from    sys.index_columns
            ) a
    cross apply
            (
            select  cast(column_id as varchar(16)) + ',' as [text()]
            from    sys.index_columns b
            where   a.object_id = b.object_id
                    and a.index_id = b.index_id
            for xml path(''),type
            ) col_list (list)
)
select  object_name(a.object_id) as TableName,asi.name as FatherIndex,bsi.name as RedundantIndex
from    ind a
join    sys.sysindexes asi
on      asi.id = a.object_id
        and asi.indid = a.index_id
join    ind b
on      a.object_id = b.object_id
        and a.object_id = b.object_id
        and len(a.list) > len(b.list)
        and left(a.list,LEN(b.list)) = b.list
join    sys.sysindexes bsi
on      bsi.id = b.object_id
        and bsi.indid = b.index_id

为您的用户带来蛋糕,以防性能“意外”降低:-)