SQL Interview Questions And Answers

What is SQL?
SQL stands for Structured Query Language , and it is used to communicate with the Database. This is a standard language used to perform tasks such as retrieval, updation, insertion and deletion of data from a database.
Standard SQL Commands are Select.

Compare SQL & PL/SQL

 

Criteria	SQL	PL/SQL
What it is	Single query or command execution	Full programming language
What it comprises	Data source for reports, web pages	Application language to build, format and display report, web pages
Characteristic	Declarative in nature	Procedural in nature
Used for	Manipulating data	Creating applications

 

What is BCP? When is it used?

It is a tool used to duplicate enormous quantity of information from tables and views. It does not facsimile the structures same as foundation to target.
BULK INSERT command helps to bring in a data folder into a record, table or view in a user-specific arrangement.

When is the UPDATE_STATISTICS command used?

This command is used, ones the processing of large data is done.
When we delete a large number of files, alteration or reproduction takes place in the tables, to be concerned of these changes we need to restructure the indexes This is done UPDATE_STATISTICS.

Explain the steps needed to Create the scheduled job?

Steps to create a Scheduled Job :

1.  Connect to the database of SQL server in SQL Server Management Studio. On the SQL Server Agent, we will find a Jobs folder.
2. Right click on jobs and choose Add New.
3. A New Job window will come into view. Give an associated name for the same.
4. Click next on the “Steps” in the left list of options. An SQL job can have multiple steps either in the form of SQL declaration or a stored practice call.
5. Click on the “Schedules” in the left list of options. An SQL job can comprise of one or supplementary schedules. It is basically the instance at which SQL job will jog itself. We can spell out returning schedules also.

    When are we going to use truncate and delete?

1. TRUNCATE is a DDL command, whereas DELETE is a DML command.
2. We can’t execute a trigger in case of TRUNCATE whilst with DELETE, we can accomplish a trigger.
3. TRUNCATE is quicker than DELETE, for the reason that when we use DELETE to delete the data, at that time it store the whole statistics in the rollback gap on or after where we can get the data back after removal. In case of TRUNCATE, it will not store data in rollback gap and will unswervingly rub it out. TRUNCATE do not recover the deleted data.
4. We can use any condition in WHERE clause using DELETE but it is not possible with TRUNCATE.5.If a table is referenced by any foreign key constraints, then TRUNCATE won’t work.

   What is a Database?

Database is nothing but an organized form of data for easy access, storing, retrieval and managing of data. This is                   also known as structured form of data which can be accessed in many ways.

 Example: School Management Database, Bank Management Database.

What are tables and Fields?

   A table is a set of data that are organized in a model with Columns and Rows. Columns can be categorized as vertical,          and Rows are horizontal. A table has specified number of column called fields but can have any number of rows which        is called record.

Example:

Table: Employee.

Field: Emp ID, Emp Name, Date of Birth.

Data: 201456, David, 11/15/1960.

 What is a primary key?

A primary key is a combination of fields which uniquely specify a row. This is a special kind of unique key, and it has implicit NOT NULL constraint. It means, Primary key values cannot be NULL.