SQL Server 如何知道要使用什么索引？

我有这个非聚集索引

CREATE NONCLUSTERED INDEX [nci_wi_StoreVariantInventory_F09B4BE817BC953FAC6861B7E46F6F51] ON [dbo].[StoreVariantInventory]
(
    [ProductId] ASC,
    [StoreId] ASC,
    [VariantId] ASC
)
INCLUDE (   [LocalInventory]) WITH (STATISTICS_NORECOMPUTE = OFF, DROP_EXISTING = OFF, ONLINE = OFF) ON [PRIMARY]
GO

而这个聚集索引

ALTER TABLE [dbo].[StoreVariantInventory] ADD  CONSTRAINT [PK_StoreVariantInventory] PRIMARY KEY CLUSTERED 
(
    [ProductId] ASC,
    [ChainId] ASC,
    [CountryCode] ASC,
    [StoreId] ASC,
    [VariantId] ASC
)WITH (STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ONLINE = OFF) ON [PRIMARY]
GO

为此表生成

SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

CREATE TABLE [dbo].[StoreVariantInventory](
    [ProductId] [bigint] NOT NULL,
    [ChainId] [nvarchar](5) NOT NULL,
    [CountryCode] [nvarchar](2) NOT NULL,
    [StoreId] [bigint] NOT NULL,
    [VariantId] [int] NOT NULL,
    [Size] [int] NOT NULL,
    [SizeRow] [nvarchar](1) NOT NULL,
    [KoncernNumber] [nvarchar](4) NOT NULL,
    [LocalInventory] [int] NOT NULL,
    [OrderedInventory] [int] NOT NULL,
    [Price] [money] NOT NULL,
    [LastUpdated] [datetime] NOT NULL,
 CONSTRAINT [PK_StoreVariantInventory] PRIMARY KEY CLUSTERED 
(
    [ProductId] ASC,
    [ChainId] ASC,
    [CountryCode] ASC,
    [StoreId] ASC,
    [VariantId] ASC
)WITH (STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY]
GO

ALTER TABLE [dbo].[StoreVariantInventory]  WITH CHECK ADD  CONSTRAINT [FK_StoreVariantInventory_Stores] FOREIGN KEY([StoreId])
REFERENCES [dbo].[Stores] ([StoreId])
GO

ALTER TABLE [dbo].[StoreVariantInventory] CHECK CONSTRAINT [FK_StoreVariantInventory_Stores]
GO

ALTER TABLE [dbo].[StoreVariantInventory]  WITH CHECK ADD  CONSTRAINT [FK_StoreVariantInventory_Variants] FOREIGN KEY([ProductId], [VariantId])
REFERENCES [dbo].[Variants] ([ProductId], [VariantId])
GO

ALTER TABLE [dbo].[StoreVariantInventory] CHECK CONSTRAINT [FK_StoreVariantInventory_Variants]
GO

如果我做一个简单的选择

select LocalInventory
from StoreVariantInventory
where ProductId=1219100110 
and VariantId = 49 
and StoreId = 9050 
and ChainId = 'F'

它通过非聚集索引查找

但是为什么它会选择非聚集索引呢？我正在做一个 100% 不适合非聚集索引的 WHERE 那么它如何使用它呢？当 WHERE 子句中的所有列都不是 100% 适合索引时，SQL Server 是否只是选择它看起来最合适的内容？没有像这里这样的索引不能 100% 适合我的 where 子句是不好的做法吗？