Mssql Interview Questions

In SQL, a cursor can be defined as a tool used widely to define a particular set of results. This result can be a set of data rows. A cursor is basically used to solve complex logic and works on a row by row manner.

Index, on the other hand, has the main function of retrieving data from tables much quicker. Indexes are created by users on columns that may be accessed frequently. This enables the user to get information quickly from the table and can be created on a single column or even a group.

• Windows Mode
• Mixed Mode

From the tools menu of SQL Server configuration properties in the security page, the modes can be changed.

• A subquery in the main query that has to be placed on the right-hand side of the comparison operator
• A subquery has to be placed parenthesis, in order to get executed first before the main query.
• It cannot have any order by clause.
• More than one subquery can be included in the main query.

• Single Row – It returns only one row.
• Multiple Row – It returns multiple rows.
• Multiple Column – It returns multiple columns to the main query.

• Insert
• Update
• Delete
• Instead of

• Binary
• Case sensitive
• Case insensitive.

Recursive stored procedure – It is defined as a process of resolving a problem where the solution occurs repetitively.This can be nested up to 32 levels.

Global temporary table – These tables are visible to all users and are deleted when the connection is closed.

• Filtering input parameters
• Use parameter collection with Dynamic SQL
• Use Parameters for Stored procedures
• In like clause, use escape characters

• ALL – It returns true if all the set of operations are true.
• AND – It returns true if the Boolean expressions are true.
• IN – It returns true if the operand is equal to one of the lists of expressions.
• ANY – It returns true if any of the set of comparisons is true.
• BETWEEN – It returns true if the operand is within a range.
• EXISTS – It returns true if the subquery contains any rows.
• LIKE – It returns true if the operand matches a pattern
• NOT – It reverses the values of any Boolean operator.
• OR – It returns true if either of the Boolean expression is true.
• SOME – It returns true if some of the set of comparisons are true.

• Select
• Insert
• Update
• Delete

DDL (Data Definition Language)

• Create
• Alter
• Drop
• Truncate

DCL (Data Control Language)

• Grant
• Revoke

TCL (Transactional Control Language)

• Commit
• RollBack
• Save Transaction

For deleting the duplicate rows we can do the following:

• Find duplicate rows using GROUP BY clause or ROW_NUMBER() function.
• Use DELETE statement to remove the duplicate rows.

The difference between the left and right outer join is as follows:

Difference between clustered index and non clustered index

• Cluster index is an index type that is used to sort table data rows on the basis of their key values. In RDBMS primary key allows us to create a clustered index based on that specific column.
• A non-clustered index (or regular b-tree index) is an index where the order of the rows does not match the physical order of the actual data. It is instead ordered by the columns that make up the index.

A foreign key is basically a primary key of another table used in the given table. It is used to create connections between two different tables. Whereas a unique key uniquely determines a row that isn’t the primary key and Creates a non-clustered index.

In SQL a cross join is also known as a cartesian product which is used to produce a result set which is the number of rows in the first table multiplied by the number of rows in the second table if no WHERE clause is used along with CROSS JOIN.

In SQL there is an object which is known as a virtual table, it is not stored directly in the file of the database. The virtual table allows SQLite for manipulating and accessing the resources by using a powerful language of SQL query. In other terms, the view in SQL is known as a virtual table. This view represents the columns and rows like any real table.

To create a view in SQL you can use the following syntax:

CREATE VIEW view_name AS
SELECT column1, column2, . . . 
FROM table_name
WHERE condition;

So, a virtual table doesn't exist physically in the database. It helps in defining things that can be used as the SQL statements just similar to a real table.

The query to return all rows in SQL is: Select * From Table_name.

The data types available in MySQL are BIT, CHAR, DATE, DATETIME, DECIMAL, ENUM, INT, JSON, etc.

Delete in MSSQL

• Deleting is one the most expensive operation, it's logged. Every row deleted is logged to the transaction log.
• Delete from ... allows to you delete specific rows.
• Delete from ... marks the row as a ghost row.
• Delete from ... does not release the space of the deleted rows, you will need to run DBCC SHRINKFILE to recover the space [single user mode].

Truncate in MSSQL

• Often people want to empty a temporary table to repopulate it with current data, then it's much faster to use the truncate statement instead of the delete statement.
• truncate table is the most efficient way of emptying a table.
• It's not possible to use the truncate table when you only want to delete some rows based on a condition.
• Truncate table does not delete rows, it deallocates the data pages and release the space.
• Truncate table cannot be used when the table is referenced by a foreign key or involved in data replication.
• Truncate table is recommended for temporary tables that need to be cleared for the next process.