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database: primary key, Clustered or NonClustered

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问题 I am creating a database in SQL server 2008, CREATE TABLE Users ( U_Id INT NOT NULL FirstName VARCHAR(50) NOT NULL, LastName VARCHAR(50) NOT NULL, Email VARCHAR(200) Password VARCHAR(50) ) I want to make U_Id the primary key. I would like to ask what is the difference between CONSTRAINT pk_UserID PRIMARY KEY (U_Id) this CONSTRAINT pk_UserID PRIMARY KEY CLUSTERED (U_Id) and this CONSTRAINT pk_UserID PRIMARY KEY NONCLUSTERED (U_Id) When to use each? I read some article but it is still unclear

How to choose the clustered index in SQL Server?

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Usually the clustered index is created in SQL Server Management Studio by setting the primary key, however my recent question about PK <-> clustered index ( Meaning of Primary Key to Microsoft SQL Server 2008 ) has shown that it is not necessary to set PK and clustered index to be equal. So how should we choose clustered indexes then? Let's have the following example: create table Customers (ID int, ...) create table Orders (ID int, CustomerID int) We would usually create the PK/CI on both ID columns but i thought about creating it for Orders in CustomerID. Is that the best choice? According

Why is there a scan on my clustered index?

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SQL 2000 The NED table has a foreign key to the SIGN table NED.RowID to SIGN.RowID The SIGN table has a foreign key to the NED table SIGN.SignID to NED.SignID The RowID and SignID are clustered primary keys that are GUIDs (not my choice) The WHERE clause is: FROM [SIGN] A INNER JOIN NED N ON A.SIGNID = N.SIGNID INNER JOIN Wizard S ON A.WizardID = S.WizardID INNER JOIN [Level] SL ON N.LevelID = SL.LevelID LEFT JOIN Driver DSL ON SL.LevelID = DSL.LevelID AND DSL.fsDeptID = @fsDeptID INNER JOIN [Character] ET ON S.CharacterID = ET.CharacterID INNER JOIN Town DS ON A.TownID = DS.TownID WHERE (A

Clustered and nonclustered indexes performance

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I have a huge table (~ 10 million rows) with clustered PK on a random uniqueidentifier column. The most operations I do with this table is inserting a new row if there is not yet a row with the same pk. (To improve performance of it I use IGNORE_DUP_KEY = ON option) My question is Can I get rid of clustered index at all on this table? I mean when I insert a row into a table with clustered index it should rearrange data physicaly. May be it is better to drop clustered index and create nonclustered index on that colum to avoid data rearrangement? I can't do an experiment on the live db because

Is it bad to have a non-clustered index that contains the primary key from the clustered index?

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问题 If you have a table with a clustered index on the Primary Key (int), is it redundant and bad to have one (ore more) non-clustered indexes that include that primary key column as one of the columns in the non-clustered index? 回答1: Actually there could be valid reasons to create a non-clustered index identical with the clustered one. The reason is that clustered indexes carry the baggage of the row data and this can make very poor row density. Ie. you can have 2-3 rows per page due to wide

How to create a Clustered Index with Entity Framework Core

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问题 From EF6.1, we have a way of specifying a clustered index on a property public class Person { [Index(IsClustered = true, IsUnique = true)] public long UserName { get; set; } } But this Index attribute does not seem to be in EF Core right now? In EF Core how do you achieve this? 回答1: From the current EF Core documentation - Indexes section: Data Annotations Indexes can not be created using data annotations. But for sure you can specify that via Fluent API (note the extension methods having

database: primary key, Clustered or NonClustered

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I am creating a database in SQL server 2008, CREATE TABLE Users ( U_Id INT NOT NULL FirstName VARCHAR(50) NOT NULL, LastName VARCHAR(50) NOT NULL, Email VARCHAR(200) Password VARCHAR(50) ) I want to make U_Id the primary key. I would like to ask what is the difference between CONSTRAINT pk_UserID PRIMARY KEY (U_Id) this CONSTRAINT pk_UserID PRIMARY KEY CLUSTERED (U_Id) and this CONSTRAINT pk_UserID PRIMARY KEY NONCLUSTERED (U_Id) When to use each? I read some article but it is still unclear to me. Can someone give me a quick explanation? The following statement: CONSTRAINT pk_UserID PRIMARY

Does the SQL Server clustered index replace the RID lookup “index”

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问题 When a table has a clustered index in SQL Server does that mean that all indexed queries will go via the clustered index? For example if I have a table with a single non-clustered index (indexing one column) and search for a row via that column it will do Index Seek -> RID -> Data row lookup -> Result But if I add a clustered index on a different column then the same query will do the following Index Seek -> Extract clustering key -> Clustered index seek -> Results This implies to me that the

Why is there a scan on my clustered index?

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问题 SQL 2000 The NED table has a foreign key to the SIGN table NED.RowID to SIGN.RowID The SIGN table has a foreign key to the NED table SIGN.SignID to NED.SignID The RowID and SignID are clustered primary keys that are GUIDs (not my choice) The WHERE clause is: FROM [SIGN] A INNER JOIN NED N ON A.SIGNID = N.SIGNID INNER JOIN Wizard S ON A.WizardID = S.WizardID INNER JOIN [Level] SL ON N.LevelID = SL.LevelID LEFT JOIN Driver DSL ON SL.LevelID = DSL.LevelID AND DSL.fsDeptID = @fsDeptID INNER JOIN

Why does SQL Server add a 4 byte integer to non-unique clustered indexes

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It is possible to define non-unique columns as clustered as well as non-clustered indexes. However, SQL Server adds a 4 byte integer to the indexed columns in case of a clustered index, if the column is not defined as unique. This is done to keep the "uniqueness" of the record internally even though two or more records may have the value for that column. Why isn't this integer necessary in case of a non-clustered index? A non-clustered index already includes the clustered index column so it can reference the exact row that it correlates to. Hence with the uniquifier on the clustered index, the