non-clustered-index

How NonClustered Index works in SQL Server

由 空扰寡人 提交于 2019-12-12 17:11:51
问题 I have a question, related to DB theory: Let's assume that we have table with 3 columns: [PersonID], [PersonName], [PersonAge] . We know that when we have a nonclustered index by one column, SQL Server orders table data in accordance with specified column and build B+ tree from it. And when we need to find the row using such an index, SQL Server scans the B++ tree by comparing one atomic data object ( int or string , for example). That is clear, how non-clustered index works and find data

Why does SQL Server use a non-clustered index over the clustered PK in a “select *” operation?

由 心已入冬 提交于 2019-12-12 11:16:26
问题 I've got a very simple table which stores Titles for people ("Mr", "Mrs", etc). Here's a brief version of what I'm doing (using a temporary table in this example, but the results are the same): create table #titles ( t_id tinyint not null identity(1, 1), title varchar(20) not null, constraint pk_titles primary key clustered (t_id), constraint ux_titles unique nonclustered (title) ) go insert #titles values ('Mr') insert #titles values ('Mrs') insert #titles values ('Miss') select * from

SQL Server creating multiple nonclustered indexes for one column vs having multiple columns in just one index

由 旧巷老猫 提交于 2019-12-12 08:04:56
问题 Suppose I have following table UserID (Identity) PK UserName - unique non null UserEmail - unique non null What is recommended for the best performance? creating non clustered index for UserName and UserEmail separately OR Just one including both the columns Please do share you thoughts why one is preferable over other. 回答1: Another important point to consider is this: a compound index (made up of multiple columns) will only be used if the n left-most columns are being referenced (e.g. in a

Azure Data Sync Clustered Index Error

由 [亡魂溺海] 提交于 2019-12-11 15:00:03
问题 We are trying to setup an Azure Database Sync group to replicate our data from an on-premise server to an Azure SQL database. This as a first step for a migration to Azure. The Sync Group and Sync Agent have all been set up. When we press the 'Sync' button we receive following error: Trigger Sync Failed: Failed to perform data sync operation: Table '[dbo].[DocumentTypeDocumentVariables]' do not have clustered index. This table did not have a clustered index but an unclustered unique primairy

Handling very big table in SQL Server Performance

由 青春壹個敷衍的年華 提交于 2019-12-11 04:48:28
问题 I'm having some troubles to deal with a very big table in my database. Before to talk about the problem, let's talk about what i want to achieve. I have two source tables : Source 1: SALES_MAN (ID_SMAN, SM_LATITUDE, SM_LONGITUDE) Source 2: CLIENT (ID_CLIENT, CLATITUDE, CLONGITUDE) Target: DISTANCE (ID_SMAN, ID_CLIENT, SM_LATITUDE, SM_LONGITUDE, CLATITUDE, CLONGITUDE, DISTANCE) The idea is to find the top N nearest SALES_MAN for every client using a ROW_NUMBER in the target table. What I'm

Non-clustered index and clustered index on the same column

由 拜拜、爱过 提交于 2019-12-10 23:29:58
问题 I came across this post in Stackoverflow. The first answer mentions something like A clustered index has all the data for the table while a non clustered index only has the column + the location of the clustered index or the row if it is on a heap (a table without a clustered index). How can a non-clustered index have the location of the clustered index? It only contains the column values sorted as nodes in a B-treee with each node pinting to the row where the column has that node-value,

How to resolve 900 key length limit index on the column which have datatype varchar(4096) in SQL Server 2005?

由 寵の児 提交于 2019-12-06 06:56:40
问题 This is the query for creating index create index idx_ncl_2 on BFPRODATTRASSOCIATION (value,attributeid) include (productid) Table structure of BFPRODATTRASSOCIATION ProdAttrAssociationId bigint no 8 ProductId bigint no 8 AttributeId bigint no 8 Value varchar no 4096 I am getting this error: The maximum key length is 900 bytes. The index ‘idx_ncl_2’ has maximum length of 1237 bytes. I have to create a nonclustered index on this column. Is there any way i can create index for the column which

Optimizing queries based on clustered and non-clustered indexes in SQL?

由 左心房为你撑大大i 提交于 2019-12-06 06:49:58
问题 I have been reading lately about how clustered index and non-clustered index works. My understanding in simple terms (correct me if wrong): The data structure that backs clustered and non-clustered index is B-Tree Clustered Index : physically sorts the data based on the index column (or key). you can have only one clustered Index per table . If no index is specified during table creation, SQL server will automatically create a clustered Index on the primary key column . Q1 : Since data is

Row Locator in Non Clustered Index

由 北城余情 提交于 2019-12-04 15:04:13
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 uniquely identify the row. If the table has a unique clustered index , the "row locator" consists of the

Optimizing queries based on clustered and non-clustered indexes in SQL?

由 こ雲淡風輕ζ 提交于 2019-12-04 14:37:40
I have been reading lately about how clustered index and non-clustered index works. My understanding in simple terms (correct me if wrong): The data structure that backs clustered and non-clustered index is B-Tree Clustered Index : physically sorts the data based on the index column (or key). you can have only one clustered Index per table . If no index is specified during table creation, SQL server will automatically create a clustered Index on the primary key column . Q1 : Since data is physically sorted based on index, there is no extra space needed here. is this correct? so what happens
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