non-clustered-index

问题 You can create a clustered index on a column other than primary key column if a nonclustered primary key constraint was specified. http://msdn.microsoft.com/en-us/library/ms186342.aspx So the above told me: I can create a clustered index on columns other than primary key. I think it also conveys that a primary key should either be a nonclustered primary key or clustered key. Is it possible a primary key is not indexed? What's more: When you create a UNIQUE constraint, a unique nonclustered

问题 I have tried to display the actual execution plan of a stored procedure as I posted here. There are 17 queries in total and here is the part of execution plan of the last query. This query is more complicated than others, because the execution time will be much shorter if I remove this part. For query 17, five "select" statements are unioned together and distinct rows are selected from the combined set. I am new to this SQL part and I am curious that: why the query cost of query 17 is so low,

问题 I have tried to display the actual execution plan of a stored procedure as I posted here. There are 17 queries in total and here is the part of execution plan of the last query. This query is more complicated than others, because the execution time will be much shorter if I remove this part. For query 17, five "select" statements are unioned together and distinct rows are selected from the combined set. I am new to this SQL part and I am curious that: why the query cost of query 17 is so low,

问题 I'm preparing a stored procedure in SQL Server. Basically, I have two tables here, table A & B, and the two tables are joined on Col4 . This stored procedure will filter table A based on the attributes in table B, say Col41 and Col42 in the where clause (both Col41 and Col42 are of float datatype). Table A: Col1 Col2 Col3 Col4 Row1 ** ** ** ** Row2 ** ** ** ** Table B: Col5 Col4 Col41 Col42 Row1 ** ** ** ** Row2 ** ** ** ** There are lots of records in the two tables, so I plan to use non

问题 I created a unique index (case description should be unique if IsDelete != 1) CREATE UNIQUE NONCLUSTERED INDEX [UniqueCaseDescription] ON [tblCases] ([fldCaseDescription] ASC) WHERE [IsDeleted] = CAST(0 AS varbinary(1)) WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] Then when I run the following procedure it throws 'UPDATE failed because the following

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

问题 I was reading about Non Clustered Index which says that " Nonclustered index contain only the values from the indexed columns and row locators that point to the actual data rows, rather than contain the data rows themselves. This means that the query engine must take an additional step in order to locate the actual data." Query - I am not clear with Row Locator . I am assuming that it is not any Primary key . There is something happening in background which has to do with Row-Locator to

问题 This question already has answers here : What are the differences between a clustered and a non-clustered index? (12 answers) Closed 4 years ago . I need to add proper index to my tables and need some help. I'm confused and need to clarify a few points: Should I use index for non-int columns? Why/why not I've read a lot about clustered and non-clustered index yet I still can't decide when to use one over the other. A good example would help me and a lot of other developers. I know that I

问题 What are the differences between a clustered and a non-clustered index ? 回答1: Clustered Index Only one per table Faster to read than non clustered as data is physically stored in index order Non Clustered Index Can be used many times per table Quicker for insert and update operations than a clustered index Both types of index will improve performance when select data with fields that use the index but will slow down update and insert operations. Because of the slower insert and update

问题 The requirement is to load 50 records in paging with all 65 columns of table "empl" with minimum IO. There are 280000+ records in table. There is only one clustered index over the PK. Pagination query is as following: WITH result_set AS ( SELECT ROW_NUMBER() OVER (ORDER BY e.[uon] DESC ) AS [row_number], e.* FROM empl e with (NOLOCK) LEFT JOIN empl_add ea with (NOLOCK) ON ea.ptid = e.ptid WHERE e.del = 0 AND e.pub = 1 AND e.sid = 2 AND e.md = 0 AND e.tid = 3 AND e.coid = 2 AND (e.cid = 102)