CREATE TABLE [dbo].[Customer](
	[Id] [int] IDENTITY(1,1) NOT FOR REPLICATION NOT NULL,
	[CustomerGuid] [uniqueidentifier] NOT NULL,
	[Username] [nvarchar](1000) NULL,
	[Email] [nvarchar](1000) NULL,
	[Password] [nvarchar](max) NULL,
	[PasswordFormatId] [int] NOT NULL,
	[PasswordSalt] [nvarchar](max) NULL,
	[AdminComment] [nvarchar](max) NULL,
	[IsTaxExempt] [bit] NOT NULL,
	[AffiliateId] [int] NOT NULL,
	[VendorId] [int] NOT NULL,
	[HasShoppingCartItems] [bit] NOT NULL,
	[Active] [bit] NOT NULL,
	[Deleted] [bit] NOT NULL,
	[IsSystemAccount] [bit] NOT NULL,
	[SystemName] [nvarchar](max) NULL,
	[LastIpAddress] [nvarchar](max) NULL,
	[CreatedOnUtc] [datetime] NOT NULL,
	[LastLoginDateUtc] [datetime] NULL,
	[LastActivityDateUtc] [datetime] NOT NULL,
	[BillingAddress_Id] [int] NULL,
	[ShippingAddress_Id] [int] NULL,
PRIMARY KEY CLUSTERED 
(
	[Id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, FILLFACTOR = 80) ON [PRIMARY]
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]
GO

declare @p__linq__0 nvarchar(4000)=N'SearchEngine'
SELECT TOP (1) 
    [Project1].[Id] AS [Id], 
    [Project1].[CustomerGuid] AS [CustomerGuid], 
    [Project1].[Username] AS [Username], 
    [Project1].[Email] AS [Email], 
    [Project1].[Password] AS [Password], 
    [Project1].[PasswordFormatId] AS [PasswordFormatId], 
    [Project1].[PasswordSalt] AS [PasswordSalt], 
    [Project1].[AdminComment] AS [AdminComment], 
    [Project1].[IsTaxExempt] AS [IsTaxExempt], 
    [Project1].[AffiliateId] AS [AffiliateId], 
    [Project1].[VendorId] AS [VendorId], 
    [Project1].[HasShoppingCartItems] AS [HasShoppingCartItems], 
    [Project1].[Active] AS [Active], 
    [Project1].[Deleted] AS [Deleted], 
    [Project1].[IsSystemAccount] AS [IsSystemAccount], 
    [Project1].[SystemName] AS [SystemName], 
    [Project1].[LastIpAddress] AS [LastIpAddress], 
    [Project1].[CreatedOnUtc] AS [CreatedOnUtc], 
    [Project1].[LastLoginDateUtc] AS [LastLoginDateUtc], 
    [Project1].[LastActivityDateUtc] AS [LastActivityDateUtc], 
    [Project1].[BillingAddress_Id] AS [BillingAddress_Id], 
    [Project1].[ShippingAddress_Id] AS [ShippingAddress_Id]
    FROM ( SELECT 
        [Extent1].[Id] AS [Id], 
        [Extent1].[CustomerGuid] AS [CustomerGuid], 
        [Extent1].[Username] AS [Username], 
        [Extent1].[Email] AS [Email], 
        [Extent1].[Password] AS [Password], 
        [Extent1].[PasswordFormatId] AS [PasswordFormatId], 
        [Extent1].[PasswordSalt] AS [PasswordSalt], 
        [Extent1].[AdminComment] AS [AdminComment], 
        [Extent1].[IsTaxExempt] AS [IsTaxExempt], 
        [Extent1].[AffiliateId] AS [AffiliateId], 
        [Extent1].[VendorId] AS [VendorId], 
        [Extent1].[HasShoppingCartItems] AS [HasShoppingCartItems], 
        [Extent1].[Active] AS [Active], 
        [Extent1].[Deleted] AS [Deleted], 
        [Extent1].[IsSystemAccount] AS [IsSystemAccount], 
        [Extent1].[SystemName] AS [SystemName], 
        [Extent1].[LastIpAddress] AS [LastIpAddress], 
        [Extent1].[CreatedOnUtc] AS [CreatedOnUtc], 
        [Extent1].[LastLoginDateUtc] AS [LastLoginDateUtc], 
        [Extent1].[LastActivityDateUtc] AS [LastActivityDateUtc], 
        [Extent1].[BillingAddress_Id] AS [BillingAddress_Id], 
        [Extent1].[ShippingAddress_Id] AS [ShippingAddress_Id]
        FROM [dbo].[Customer] AS [Extent1] 
        WHERE ([Extent1].[SystemName] = @p__linq__0) OR (([Extent1].[SystemName] IS NULL) AND (@p__linq__0 IS NULL))
    )  AS [Project1]
    ORDER BY [Project1].[Id] ASC

select SystemName, count(*) cnt
from Customer
group by SystemName
order by 1

SystemName	cnt
NULL	5603609
ArrHealthyCheck	1
BackgroundTask	1
SearchEngine	1
Warmup	1

EXEC sp_updatestat

DBCC SHOW_STATISTICS ('Customer', [_WA_Sys_00000010_36B12243]); 
Name                        Updated              Rows       Rows Sampled  Steps  Density   Average key length  String Index  Filter Expression  Unfiltered Rows
--------------------------- ---- ------------ 	----------- ------------- ------ --------- ------------------- ------------- ------------------ --------------------------
_WA_Sys_00000010_36B12243   May 20 2019  4:24PM  5584561    116167        1      0         0                   YES           NULL               5584561

All density   Average Length Columns
------------- -------------- -----------
1             0              SystemName

RANGE_HI_KEY RANGE_ROWS    EQ_ROWS       DISTINCT_RANGE_ROWS  AVG_RANGE_ROWS
------------ ------------- ------------- -------------------- --------------
NULL         0             5584561       0                    1  

update statistics Customer [_WA_Sys_00000010_36B12243] with fullscan

DBCC SHOW_STATISTICS ('Customer', [_WA_Sys_00000010_36B12243]); 
Name                         Updated              Rows     Rows Sampled  Steps  Density  Average key length String Index Filter Expression  Unfiltered Rows
---------------------------- -------------------- -------- ------------- ------ -------- ------------------ ------------ ------------------ --------------------
_WA_Sys_00000010_36B12243    May 21 2019  1:40AM  5604477  5604477       5      0        1.67723E-05        YES          NULL               5604477

All density   Average Length Columns
------------- -------------- ---------------
0.2           1.67723E-05    SystemName

RANGE_HI_KEY     RANGE_ROWS    EQ_ROWS       DISTINCT_RANGE_ROWS  AVG_RANGE_ROWS
---------------- ------------- ------------- -------------------- --------------
NULL             0             5604473       0                    1
ArrHealthyCheck  0             1             0                    1
BackgroundTask   0             1             0                    1
SearchEngine     0             1             0                    1
Warmup           0             1             0                    1

select @@version

create statistics _WA_Sys_00000010_36B12243_Filtered ON Customer(SystemName) WHERE SystemName IS NOT NULL