17th October 2019

stackoverflow

13

What is clustered index and non clustered index?

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A clustered index is a special type of index that reorders the way records in the table are physically stored. Therefore table can have only one clustered index. The leaf nodes of a clustered index contain the data pages. Instead, the leaf nodes contain index rows.

Herein, what are B trees used for?

A B-tree is a tree data structure that keeps data sorted and allows searches, insertions, and deletions in logarithmic amortized time. Unlike self-balancing binary search trees, it is optimized for systems that read and write large blocks of data. It is most commonly used in database and file systems.

What is a B tree index?

In computer science, a B-tree is a self-balancing tree data structure that keeps data sorted and allows searches, sequential access, insertions, and deletions in logarithmic time. The B-tree is a generalization of a binary search tree in that a node can have more than two children.

What is a B+ tree?

A B+ tree is an N-ary tree with a variable but often large number of children per node. A B+ tree consists of a root, internal nodes and leaves. A B+ tree can be viewed as a B-tree in which each node contains only keys (not key–value pairs), and to which an additional level is added at the bottom with linked leaves.

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How many clustered and non clustered index can be applied to a table?

Number of Clustered indexes in SQL 2005 is one and 249 non clustered indexes, altogether 250 indexes for a table in SQL Server 2005. In SQL Server 2008, the maximum is 1000. The answer IS one. Each table can only have one in SQL Server.

2

What is a non clustered index?

A clustered index is a special type of index that reorders the way records in the table are physically stored. Therefore table can have only one clustered index. The leaf nodes of a clustered index contain the data pages. Instead, the leaf nodes contain index rows.

3

What is the difference between commit and rollback?

Difference Between Rollback and Commit in Oracle. To undo the work/changes that are committed or done by COMMIT clause we use the ROLLBACK Command. It rollbacks all the changes of the current transactions. In other words ROLLBACK restore the state of the database to the last commit point.

4

What is clustered and nonclustered index?

An index contains keys built from one or more columns in the table or view. These keys are stored in a structure (B-tree) that enables SQL Server to find the row or rows associated with the key values quickly and efficiently. A table or view can contain the following types of indexes: Clustered.

5

What do you mean by cursor in SQL?

A cursor is a temporary work area created in the system memory when a SQL statement is executed. A cursor contains information on a select statement and the rows of data accessed by it. This temporary work area is used to store the data retrieved from the database, and manipulate this data.

6

How does Index work in SQL Server?

Indexes are created on columns in tables or views. For example, if you create an index on the primary key and then search for a row of data based on one of the primary key values, SQL Server first finds that value in the index, and then uses the index to quickly locate the entire row of data.

7

What is a clustered index?

A clustered index is a special type of index that reorders the way records in the table are physically stored. Therefore table can have only one clustered index. The leaf nodes of a clustered index contain the data pages. Instead, the leaf nodes contain index rows.”

8

What is the difference between primary key and unique key?

Primary Key (PK): It's also a column or group of columns that can identify a uniqueness in a row. So the Primary key is just another name for unique key, but the default implementation in SQL Server is different for Primary and Unique Key. By Default: PK creates a Clustered index and UK creates a Non Clustered Index.

9

Why do we use index in SQL?

An index is used to speed up the performance of queries. It does this by reducing the number of database data pages that have to be visited/scanned. In SQL Server, a clustered index determines the physical order of data in a table.

10

What are the triggers in SQL?

A trigger is a special kind of stored procedure that automatically executes when an event occurs in the database server. DML triggers execute when a user tries to modify data through a data manipulation language (DML) event. DML events are INSERT , UPDATE , or DELETE statements on a table or view.

11

What is a cluster in SQL Server?

A cluster is a schema object that contains data from one or more tables, all of which have one or more columns in common. Oracle Database stores together all the rows from all the tables that share the same cluster key.

12

Is a primary key and index?

The primary key column cannot allow NULL values. When you create a UNIQUE constraint, a unique nonclustered index is created to enforce a UNIQUE constraint by default. You can specify a unique clustered index if a clustered index on the table does not already exist.

13

Can we create non unique clustered index?

So, when you create the clustered index - it must be unique. But, SQL Server doesn't require that your clustering key is created on a unique column. You can create it on any column(s) you'd like. Internally, if the clustering key is not unique then SQL Server will “uniquify” it by adding a 4-byte integer to the data.

14

What is a B tree index?

In computer science, a B-tree is a self-balancing tree data structure that keeps data sorted and allows searches, sequential access, insertions, and deletions in logarithmic time. The B-tree is a generalization of a binary search tree in that a node can have more than two children.

15

How many non clustered indexes can be created on a table?

As we all know there are two types of indexes that can be created in Database namely CLUSTERED and NON-CLUSTERED. SQL Server allows maximum up to 249 NON-CLUSTERED indexes that can be created in single table. This has been increased to 999 in SQL Server 2008 R2 version for both 32-bit and 64-bit server.

16

What are the normalization?

Normalization of Database. Normalization is a systematic approach of decomposing tables to eliminate data redundancy(repetition) and undesirable characteristics like Insertion, Update and Deletion Anamolies. It is a multi-step process that puts data into tabular form, removing duplicated data from the relation tables.

17

What is the use of primary key in SQL?

A primary key is a field in a table which uniquely identifies each row/record in a database table. Primary keys must contain unique values. A primary key column cannot have NULL values. A table can have only one primary key, which may consist of single or multiple fields.

18

What is the use of transaction log?

Transaction log backups can be used to restore a database to a specific point in time. A transaction log backup alone is not sufficient to restore a database. A backup of the data file is required as well. The data file backups are applied first.

19

What is with CTE as in SQL?

SQL Server CTE Basics. Introduced in SQL Server 2005, the common table expression (CTE) is a temporary named result set that you can reference within a SELECT, INSERT, UPDATE, or DELETE statement. You can also use a CTE in a CREATE VIEW statement, as part of the view's SELECT query.

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