用于查找冗余索引的T-SQL

Question

是否有人知道可以检测整个数据库中的冗余索引的T-SQL脚本？表中冗余索引的示例如下:

Index 1: 'ColumnA', 'ColumnB', 'ColumnC'
Index 2: 'ColumnA', 'ColumnB'

忽略其他注意事项,例如列的宽度和覆盖索引,索引2将是多余的.

谢谢.

Answer 1

有些情况下冗余不成立.例如,假设ColumnC是一个huuge字段,但有时您必须快速检索它.您index 1不需要键查找:

select ColumnC from YourTable where ColumnnA = 12

另一方面index 2,它要小得多,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:-)