What is a query?

Short Question

741

Answer:

A DB query is a code written in order to get the information back from the database. Query can be designed in such a way that it matched with our expectation of the result set. Simply, a question to the Database.

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831. What is subquery?

Answer: A subquery is a query within another query. The outer query is called as main query, and inner query is called subquery. SubQuery is always executed first, and the result of subquery is passed on to the main query.

# Tutorial: SQL Basic Overview

Question: SQL Introduction Short

832. What are the types of subquery?

Answer:

There are two types of subquery – Correlated and Non-Correlated.

A correlated subquery cannot be considered as independent query, but it can refer the column in a table listed in the FROM the list of the main query.

A Non-Correlated sub query can be considered as independent query and the output of subquery are substituted in the main query.

# Tutorial: Query Language

Question: SQL Introduction Short

833. What is a stored procedure?

Answer: A stored procedure is a pre-compiled set of one or more SQL statements that are stored on SQL Server. The benefit of Stored Procedures is that they are executed on the server-side and perform a set of actions, before returning the results to the client-side. This allows a set of actions to be executed with minimum time and also reduces the network traffic. Hence stored procedure improves performance to execute SQL statements.

# Tutorial: Stored Procedures Introduction

Question: SQL Stored Procedures Short

841. When Right Join gives result like Left Join?

# Tutorial: Right Join

Question: SQL Joins Long

842. When Left Join gives result like Right Join?

# Tutorial: Left Join

Question: SQL Joins Long

843. When to use single-column index or a composite index?

Answer:

To create a single-column index or a composite index, take into consideration the column(s) that you may use very frequently in a query's WHERE clause as filter conditions.

Should there be only one column used, a single-column index should be the choice. Should there be two or more columns that are frequently used in the WHERE clause as filters, the composite index would be the best choice.

# Tutorial: Index

Question: SQL Constraints Short

844. When should indexes be avoided?

# Tutorial: Index

Question: SQL Constraints Long

845. When should indexes be created?

Answer:

A column contains a wide range of values
A column does not contain a large number of null values
One or more columns are frequently used together in a where clause or a join condition

# Tutorial: Index

Question: SQL Constraints Short

881. How to get the last generated identity column value in SQL Server

# Tutorial: Identity Column in SQL Server

Question: SQL Constraints Long

882. JOIN or INNER JOIN in SQL Server

# Tutorial: Inner Join

Question: SQL Joins Long

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