Interview Questions and answers - SQL Server Day 6


Question: When we used UPDATE_STATISTICS commands in the SQL server?
Answer: When bulk changes are done in your database like INSERT, UPDATE, and DELETE because bulk changes may increase your index view fragmentation. UPDATE_STATISTICS Updates query optimization statistics on a table or indexed view.
Question: What is view in SQL Server?
Answer: The view is a virtual table that contains one or more than one field of more than one physical table. The view is used for de-normalization purposes. This is used to join multiple tables and get the data.
Question: What is the property of the relational table in SQL Server?
Answer:
1.       Values are atomic.
2.       Column values are of the same kind.
3.       Each row is unique.
4.       The sequence of columns is insignificant.
5.       The sequence of rows is insignificant.
6.       Each column must have a unique name.
Question: Explain the different types of lock-in SQL Server?
Answer: The following locks are available in SQL Server.
Shared (S)
Used for reading operations those do not change or update data, such as a SELECT statement.
Update (U)
Used on resources that can be updated. Prevents a common form of deadlock that occurs when multiple sessions are reading, locking and potentially updating resources later.
Exclusive (X)
Used for data-modification Operations, such as INSERT, UPDATE, or DELETE. Ensures that multiple updates cannot be made to the same resource at the same time.
Intent
Used to establish a lock hierarchy. The types of intent locks are: intent shared (IS), intent exclusive (IX), and shared with intent exclusive (SIX).
Schema
Used when an operation dependent on the schema of a table is executing. The types of schema locks are schema modification (Sch-M) and schema stability (Sch-S).
Bulk Update (BU)
Used when bulk copying data into a table, and the TABLOCK hint is specified.
Key-range
Protects the range of rows read by a query when using the serializable transaction isolation level. Ensures that other transactions cannot insert rows that would qualify for the queries of the serializable transaction if the questions were rerun.
Question: What is the DBCC command in SQL Server?
Answer: DBCC Stands for Database Consistency Checker. These commands are used to check the consistency of the database, like validation tasks, maintenance, and status checks.
For example –
DBCC CHECKALLOC – Responsible for checking that all pages are correctly allocated in the database.
DBCC CHECKDB – Responsible for checking the integrity & allocation of specific objects in a database.
DBCC SQLPERF- Responsible to show transaction log statistics.
DBCC SQLFILEGROUP – Responsible for checking all the tables file groups for any design.

PostgreSQL-Query: Sort result set by specific field values using ORDER BY Clause

Problem: Suppose we have a book_inventory table which has some columns such as id, isbn, title, author, publisher, publish_date, etc.. whe...