Heap storage has nothing to do with these heaps. Heap just means records themselves are not ordered (i. e. not linked to one another). When you insert a record, it just gets inserted into the free space the database finds. Updating a row in a heap based table does not affect other records (though it … Read more
A big reason for a clustered index is when you often want to retrieve rows for a range of values for a given column. Because the data is physically arranged in that order, the rows can be extracted very efficiently. Something like a GUID, while excellent for a primary key, could be positively detrimental to … Read more
The following statement: CONSTRAINT pk_UserID PRIMARY KEY (U_Id) Is the same as this one: CONSTRAINT pk_UserID PRIMARY KEY CLUSTERED (U_Id) You can only have the table data physicality ordered by one of the indexes, and by default that index is the one used for the primary key (the primary key unique constraint is always supported … Read more
Drop the clustered index, then recreate the primary key as non-clustered: ALTER TABLE dbo.Config DROP CONSTRAINT PK_Config go ALTER TABLE dbo.Config ADD CONSTRAINT PK_Config PRIMARY KEY NONCLUSTERED (ConfigID)
Note that PostgreSQL uses the term “clustered index” to use something vaguely similar and yet very different to SQL Server. If a particular index has been nominated as the clustering index for a table, then psql’s \d command will indicate the clustered index, e.g., Indexes: “timezone_description_pkey” PRIMARY KEY, btree (timezone) CLUSTER PostgreSQL does not nominate … Read more
Look in sys.dm_db_index_usage_stats. The columns last_user_xxx will contain the last time the table was accessed from user requests. This table resets its tracking after a server restart, so you must leave it running for a while before relying on its data.
They don’t have to be unique but it certainly is encouraged. I haven’t encountered a scenario yet where I wanted to create a CI on a non-unique column. What happens if you create a CI on a non-unique column If the clustered index is not a unique index, SQL Server makes any duplicate keys unique … Read more
I just want to put in a word of warning: please very carefully pick your clustered index! Every “regular” data table ought to have a clustered index, since having a clustered index does indeed speed up a lot of operations – yes, speed up, even inserts and deletes! But only if you pick a good … Read more
A clustered index alters the way that the rows are stored. When you create a clustered index on a column (or a number of columns), SQL server sorts the table’s rows by that column(s). It is like a dictionary, where all words are sorted in alphabetical order in the entire book. A non-clustered index, on … Read more
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 … Read more