What are the important topics in SQL for interview?

What do I need to know for SQL interview?

SQL Interview Questions

  • What is the difference between SQL and MySQL?
  • What are the different subsets of SQL?
  • What do you mean by DBMS? …
  • What do you mean by table and field in SQL?
  • What are joins in SQL?
  • What is the difference between CHAR and VARCHAR2 datatype in SQL?
  • What is the Primary key?
  • What are Constraints?

What are the important topics in SQL?

The 10 areas we will cover in this article:

  • Key elements of a database.
  • Relational Keys.
  • Select Queries.
  • Joins.
  • Data Modelling.
  • Fact and Dimension Table Types.
  • Star Schema.
  • Snow Flake Schema.

Where should I prepare for SQL interview?

1. Practice SQL Queries

  • Hop on over to the SQL Practice course on LearnSQL.com. …
  • Once you’ve got that under your belt, spend some time studying the type of SQL questions employers are likely to ask in your interview. …
  • Another great place to get some SQL practice is w3resource.com.

How would you describe SQL project in interview?

For explaining the project in an interview, start off by giving out an intro which briefly describes the problem, and what you set out to achieve. Then, enter the research part, the concepts you worked out, and later the tools and various technicalities involved.

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What are the 5 basic SQL commands?

There are five types of SQL commands: DDL, DML, DCL, TCL, and DQL.

  • Data Definition Language (DDL) DDL changes the structure of the table like creating a table, deleting a table, altering a table, etc. …
  • Data Manipulation Language. …
  • Data Control Language. …
  • Transaction Control Language. …
  • Data Query Language.

What is surrogate key in SQL?

A Surrogate Key in SQL Server is a unique identifier for each row in the table. It is just a key. Using this key we can identify a unique row. There is no business meaning for Surrogate Keys. … A Surrogate Key is just a unique identifier for each row and it may use as a Primary Key.

Why * is used in SQL?

The second part of a SQL query is the name of the column you want to retrieve for each record you are getting. You can obviously retrieve multiple columns for each record, and (only if you want to retrieve all the columns) you can replace the list of them with * , which means “all columns”.

What are SQL concepts?

Structured Query Language (SQL) is a powerful database tool that is used to perform operations such as create, maintain and retrieve data stored in the relational database. It is basically a standard language for data manipulation in a Database Management System (DBMS).

Is SQL difficult?

Generally speaking, SQL is an easy language to learn. If you understand programming and already know some other languages, you can learn SQL in a few weeks. If you’re a beginner, completely new to programming, it can take longer.

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What is unique key in SQL?

A unique key is a set of one or more than one fields/columns of a table that uniquely identify a record in a database table. You can say that it is little like primary key but it can accept only one null value and it cannot have duplicate values.

What is SQL Indexing?

A SQL index is used to retrieve data from a database very fast. Indexing a table or view is, without a doubt, one of the best ways to improve the performance of queries and applications. A SQL index is a quick lookup table for finding records users need to search frequently.

What are SQL constraints?

SQL constraints are a set of rules implemented on tables in relational databases to dictate what data can be inserted, updated or deleted in its tables. This is done to ensure the accuracy and the reliability of information stored in the table.

What is injection in SQL?

SQL injection is a web security vulnerability that allows an attacker to interfere with the queries that an application makes to its database. It generally allows an attacker to view data that they are not normally able to retrieve.

What are views in SQL?

In SQL, a view is a virtual table based on the result-set of an SQL statement. A view contains rows and columns, just like a real table. The fields in a view are fields from one or more real tables in the database.

How do I find duplicates in SQL?

How to Find Duplicate Values in SQL

  1. Using the GROUP BY clause to group all rows by the target column(s) – i.e. the column(s) you want to check for duplicate values on.
  2. Using the COUNT function in the HAVING clause to check if any of the groups have more than 1 entry; those would be the duplicate values.
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