Skip to main content

Difference between Clustered index and Non clustered index

  • When you create a new table there will not be any index on it. A table without any clustered index is called a Heap Table. Heap table contains data in unsorted way, that means the data rows are not stored in any particular order. The data pages are not linked in a linked list. 
  • Clustered Index: A clustered index is a special type of index that reorders the way records in the table are physically stored. There for table can have only one clustered index. The leaf nodes of a clustered index contain the actual data. The clustered index is implemented as a B-tree index structure that supports fast retrieval of the rows, based on their clustered index key values. The pages in each level of the index, including the data pages in the leaf level, are linked in a doubly-linked list. 
  • Non Clustered Index:  A non-clustered index is a special type of index in which the logical order of the index doesn't match with physical order of the rows on disk. The leaf node of a clustered index does not consist of data pages. The leaf nodes contain index rows.
• In which scenarios you would use a Heap Table?
Heap table are used as staging tables, during import/export/ETL processes. Typically get truncated before the process starts. Data population happen faster, if large amount of data is there data retrieval will be very slow.



Labels:

Comments

Post a Comment

Popular posts from this blog

SQL Server script Error: Insufficient result space to convert uniqueidentifier value to char.

Error:    G etting below error while trying to copy data from one table to another: Msg 8170, Level 16, State 2, Line 1004  Insufficient result space to convert uniqueidentifier value to char.   Fix: UserID column which would be having Unique identifier data require more space (36 character). Size is specified as 15 here. To fix it just specify 36 as varchar length or specify Uniqueidentifier as data type for UserID  column.
Post a Comment
Read more

While executing Select query to pull data from a different server, SQL Server is showing following error:

Msg 7202, Level 11, State 2, Line 1 Could not find server 'LAPTOP-09O6NE3K\SQLEXPRESS03' in sys.servers. Verify that the correct server name was specified. If necessary, execute the stored procedure sp_addlinkedserver to add the server to sys.servers. Completion time: 2024-02-05T17:18:24.6869756+05:30 Solution: Step1:  Check if the server is available in the sys.servers table SELECT name from sys.servers Step2:  If no, add the new server to the sys.servers table EXEC sp_addlinkedserver @server = 'server name' Eg" EXEC sp_addlinkedserver @server = 'LAPTOP-09O6NE3K\SQLEXP RESS03' Step3:  Recheck if the new server name is added to the sys.servers table. If yes, try then rerunning the select query which throwed the error. Now it should pull data from the table in the new server successfully.    
Post a Comment
Read more

Overcoming Performance Issues with Memory Optimized tables - SQL Server 2014 CPT2

Overcoming Performance Issues with Memory Optimized tables - SQL Server 2014 CPT2 1.        Problem Tuning    databases so that they provide the best possible performance is one of the most important responsibilities of database administrators (DBAs).   SQL Server was originally designed at a time when it could be assumed that main memory was very expensive, so data needed to reside on disk except when it was actually needed for processing.   As the amount data    within an organization increases, accumulation of data affects the productivity of DBAs, who must spend considerable time and effort on achieving the high levels of database performance. 2.        Solution Nowadays memory is much cheaper and a working data set can be stored entirely in memory. The assumption that main memory was very expensive is no longer valid as memory prices have dropped enormously. Memory-opti...
Post a Comment
Read more