clustered-index

问题 In MySQL, how can we tell if an index of a table is clustered or not? We can use show index from table-name to get information about the table's indexes. But I don't find it shows whether each index is clustered or nonclustered. This is for the purpose of If a table in MySQL has any index, must the table have a clustered index? 回答1: In the default storage engine, InnoDB, the PRIMARY KEY index is always the clustered index. If you don't have a PRIMARY KEY, it's the first UNIQUE KEY index on

问题 My company has committed the sin of using GUIDs as Primary Keys on our Azure SQL Database tables (it is actually worse than that: we used VARCHAR(36) instead of UNIQUEIDENTIFIER). As such, we end up with fragmented indexes. They looked like this: CREATE TABLE OldTable ( Id VARCHAR(36) PRIMARY KEY CLUSTERED NOT NULL DEFAULT NEWID(), CreateTime DATETIME2 NOT NULL, ... ) I "fixed" the problem by creating new tables. This time, I used an immutable, ever-increasing DATETIME2 (e.g. CreateTime)

问题 I am working on MS SQL server. I have a table called "User" with three columns and default index which is created with Primary Key of the table, of UserId. I have a word file that contains user information line by line. There are almost 10000 lines. I have a program that reads the user information from the word file and inserts it into the database. It is written with C# in visual studio. The program uses repository and unitofwork pattern. The program workflow is as follows: 1) read a single

问题 Many posts like this stackoverflow link claim that there is no concept of a clustered index in PostgreSQL. However, the PostgreSQL documentation contains something similar. A few people claim it is similar to a clustered index in SQL Server. Do you know what the exact difference between these two is, if there is any? 回答1: A clustered index or index organized table is a data structure where all the table data are organized in index order, typically by organizing the table in a B-tree structure

问题 Many posts like this stackoverflow link claim that there is no concept of a clustered index in PostgreSQL. However, the PostgreSQL documentation contains something similar. A few people claim it is similar to a clustered index in SQL Server. Do you know what the exact difference between these two is, if there is any? 回答1: A clustered index or index organized table is a data structure where all the table data are organized in index order, typically by organizing the table in a B-tree structure

问题 The goal of using a sequential guid is so you can use clustered indexes without the high levels of fragmentation that would normally exist in a clustered index if it was a regular guid, correct? 回答1: Yes, you are correct. 回答2: First to clarify, a primary key and clustered index are 2 separate and distinct things, i.e. one is not coupled to the other (PKs can be nonclustered, clustered indexes can be non-PKs). That given, I think you're asking more "Should a Sequential GUID be used as a

问题 The goal of using a sequential guid is so you can use clustered indexes without the high levels of fragmentation that would normally exist in a clustered index if it was a regular guid, correct? 回答1: Yes, you are correct. 回答2: First to clarify, a primary key and clustered index are 2 separate and distinct things, i.e. one is not coupled to the other (PKs can be nonclustered, clustered indexes can be non-PKs). That given, I think you're asking more "Should a Sequential GUID be used as a

问题 IMO, please correct me... the leaf of clustered index contains the real table row, so full clustered index, with intermediate leaves, contain much more data than the full table(?) Why/when/how is ever whole clustered index scan chosen over the full table scan? How is clustered index on CUSTOMER_ID column used in SELECT query which does not contain it in either SELECT list or in WHERE condition [1]? Update: Should I understand that full clustered scan is faster than full table scan because

问题 I'm trying to define a property that is not the id as a clustered index in nhibernate, yet I've found no way of doing this. Could anyone give me a pointer of how this is done, or it is something not currently available in nhibernate? Thanks in advance 回答1: You can use <database-object> to create indexes and other artifacts. http://nhibernate.info/doc/nhibernate-reference/mapping.html#mapping-database-object 来源： https://stackoverflow.com/questions/3070355/setting-clustered-index-in-nhibernate

问题 I'm learning more about indexes in general, and clustered indexes in particular. In this article by Markus Winand, he makes an excellent case for not using the primary key of a table as the clustering key. He stresses index-only scans over using clustered indexes, and shows how you can use non-clustered indexes to get really fast results. Can someone explain why Entity Framework code-first does not provide the means to store a table as a non-clustered-index? What are the benefits of having