File Name: relational database interview questions and answers .zip
Most popular commercial and open source databases currently in use are based on the relational model. A database is a logically coherent collection of data with some inherent meaning, representing some aspect of real world and which is designed, built and populated with data for a specific purpose. Is This Answer Correct? It is a collection of programs that enables user to create and maintain a database.
DBMS is a collection of programs that facilitates users to create and maintain a database. In other words, DBMS provides us an interface or tool for performing different operations such as the creation of a database, inserting data into it, deleting data from it, updating the data, etc. DBMS is a software in which data is stored in a more secure way as compared to the file-based system. Using DBMS, we can overcome many problems such as- data redundancy, data inconsistency, easy access, more organized and understandable, and so on.
A Database is a logical, consistent and organized collection of data that it can easily be accessed, managed and updated. Databases, also known as electronic databases are structured to provide the facility of creation, insertion, updating of the data efficiently and are stored in the form of a file or set of files, on the magnetic disk, tapes and another sort of secondary devices. Database mostly consists of the objects tables , and tables include of the records and fields.
Fields are the basic units of data storage, which contain the information about a particular aspect or attribute of the entity described by the database. DBMS is used for extraction of data from the database in the form of the queries.
The collection of database and DBMS software together is known as a database system. Through the database system, we can perform many activities such as-. The data can be stored in the database with ease, and there are no issues of data redundancy and data inconsistency. The data will be extracted from the database using DBMS software whenever required. So, the combination of database and DBMS software enables one to store, retrieve and access data with considerate accuracy and security. The Checkpoint is a type of mechanism where all the previous logs are removed from the system and permanently stored in the storage disk.
There are two ways which can help the DBMS in recovering and maintaining the ACID properties, and they are- maintaining the log of each transaction and maintaining shadow pages. So, when it comes to log based recovery system, checkpoints come into existence. Checkpoints are those points to which the database engine can recover after a crash as a specified minimal point from where the transaction log record can be used to recover all the committed data up to the point of the crash.
A checkpoint is like a snapshot of the DBMS state. Using checkpoints, the DBMS can reduce the amount of work to be done during a restart in the event of subsequent crashes. Checkpoints are used for the recovery of the database after the system crash. Checkpoints are used in the log-based recovery system. When due to a system crash we need to restart the system then at that point we use checkpoints. So that, we don't have to perform the transactions from the very starting.
Physical structure or physical storage structure implies to the memory manager of the DBMS, and it describes how the data stored on disk. Unary operations are those operations which use single operands. It is used to maintain the data records and indices in tables. RDBMS is the system that enables you to perform different operations such as- update, insert, delete, manipulate and administer a relational database with minimal difficulties.
Database language implies the queries that are used for the update, modify and manipulate the data. The Data model is specified as a collection of conceptual tools for describing data, data relationships, data semantics and constraints. These models are used to describe the relationship between the entities and their attributes. A Relation Schema is specified as a set of attributes.
It is also known as table schema. It defines what the name of the table is. Relation schema is known as the blueprint with the help of which we can explain that how the data is organized into tables. This blueprint contains no data. A relation is specified as a set of tuples. A relation is the set of related attributes with identifying key attributes. Let r be the relation which contains set tuples t1, t2, t3, The degree of relation is a number of attribute of its relation schema.
A degree of relation is also known as Cardinality it is defined as the number of occurrence of one entity which is connected to the number of occurrence of other entity.
There are three degree of relation they are one-to-one , one-to-many 1:M , many-to-one M:M. The Relationship is defined as an association among two or more entities. There are three type of relationships in DBMS-. One-To-One : Here one record of any object can be related to one record of another object. One-To-Many many-to-one : Here one record of any object can be related to many records of other object and vice versa.
Many-to-many : Here more than one records of an object can be related to n number of records of another object. Data abstraction in DBMS is a process of hiding irrelevant details from users. Because database systems are made of complex data structures so, it makes accessible the user interaction with the database.
For example : We know that most of the users prefer those systems which have a simple GUI that means no complex processing. So, to keep the user tuned and for making the access to the data easy, it is necessary to do data abstraction. In addition to it, data abstraction divides the system in different layers to make the work specified and well defined. Physical level : It is the lowest level of abstraction. It describes how data are stored. Logical level : It is the next higher level of abstraction.
It describes what data are stored in the database and what the relationship among those data is. View level : It is the highest level of data abstraction. It describes only part of the entire database. For example- User interacts with the system using the GUI and fill the required details, but the user doesn't have any idea how the data is being used. Data Definition Language DDL is a standard for commands which defines the different structures in a database.
These commands are used for updating data into the database. DData Manipulation Language DML is a language that enables the user to access or manipulate data as organized by the appropriate data model. DML Compiler is required because the DML is the family of syntax element which is very similar to the other programming language which requires compilation. So, it is essential to compile the code in the language which query evaluation engine can understand and then work on those queries with proper output.
Relational Algebra is a Procedural Query Language which contains a set of operations that take one or two relations as input and produce a new relationship. Relational algebra is the basic set of operations for the relational model.
The decisive point of relational algebra is that it is similar to the algebra which operates on the number. Relational Calculus is a Non-procedural Query Language which uses mathematical predicate calculus instead of algebra. Relational calculus doesn't work on mathematics fundamentals such as algebra, differential, integration, etc.
That's why it is also known as predicate calculus. The term query optimization specifies an efficient execution plan for evaluating a query that has the least estimated cost. The concept of query optimization came into the frame when there were a number of methods, and algorithms existed for the same task then the question arose that which one is more efficient and the process of determining the efficient way is known as query optimization.
Once the DBMS informs the user that a transaction has completed successfully, its effect should persist even if the system crashes before all its changes are reflected on disk. This property is called durability. Durability ensures that once the transaction is committed into the database, it will be stored in the non-volatile memory and after that system failure cannot affect that data anymore.
Normalization is a process of analysing the given relation schemas according to their functional dependencies. It is used to minimize redundancy and also used to minimize insertion, deletion and update distractions.
Normalization is considered as an essential process as it is used to avoid data redundancy, insertion anomaly, updation anomaly, deletion anomaly. Denormalization is the process of boosting up database performance and adding of redundant data which helps to get rid of complex data. Denormalization is a part of database optimization technique. This process is used to avoid the use of complex and costly joins. Denormalization doesn't refer to the thought of not to normalize instead of that denormalization takes place after normalization.
In this process, firstly the redundancy of the data will be removed using normalization process than through denormalization process we will add redundant data as per the requirement so that we can easily avoid the costly joins.
Functional Dependency is the starting point of normalization. It exists when a relation between two attributes allow you to determine the corresponding attribute's value uniquely. The functional dependency is also known as database dependency and defines as the relationship which occurs when one attribute in a relation uniquely determines another attribute.
E-R model is a short name for the Entity-Relationship model. This model is based on the real world. It contains necessary objects known as entities and the relationship among these objects. Here the primary objects are the entity, attribute of that entity, relationship set, an attribute of that relationship set can be mapped in the form of E-R diagram.
In E-R diagram, entities are represented by rectangles, relationships are represented by diamonds, attributes are the characteristics of entities and represented by ellipses, and data flow is represented through a straight line. The Entity is a set of attributes in a database. An entity can be a real-world object which physically exists in this world. All the entities have their attribute which in the real world considered as the characteristics of the object.
For example: In the employee database of a company, the employee, department, and the designation can be considered as the entities. These entities have some characteristics which will be the attributes of the corresponding entity.
An entity type is specified as a collection of entities, having the same attributes. Entity type typically corresponds to one or several related tables in the database. A characteristic or trait which defines or uniquely identifies the entity is called entity type.
SQL programming skills are highly desirable and required in the market, as there is a massive use of Database Management Systems DBMS in almost every software application. In order to get a job, candidates need to crack the interview in which they are asked various SQL interview questions. Following is a curated list of SQL interview questions and answers, which are likely to be asked during the SQL interview. Candidates are likely to be asked basic SQL interview questions to advance level SQL questions depending on their experience and various other factors. The below list covers all the SQL interview questions for freshers as well as SQL interview questions for experienced level candidates and some SQL query interview questions.
SQL is one of the most widely used languages. Almost all biggest names in the tech industry such as Uber, Netflix, Airbnb, etc. The reason for the popularity of SQL is that most of the professions require knowledge of database connectivity. Also, in all technical interviews, 30—40 percent of questions will be from SQL. So, this blog lists all the top SQL interview questions.
DBMS is a collection of programs that facilitates users to create and maintain a database. In other words, DBMS provides us an interface or tool for performing different operations such as the creation of a database, inserting data into it, deleting data from it, updating the data, etc. DBMS is a software in which data is stored in a more secure way as compared to the file-based system. Using DBMS, we can overcome many problems such as- data redundancy, data inconsistency, easy access, more organized and understandable, and so on. A Database is a logical, consistent and organized collection of data that it can easily be accessed, managed and updated.
Now the client wants to insert a record after the identity value 7 with its identity value starting from Write a single query to calculate the sum of all positive values of x and he sum of all negative values of x. Although there are 4 customers not referred by Jane Smith including Jane Smith herself , the query will only return one: Pat Richards.
A prearranged collection of figures known as data is called database. Database Management Systems DBMS are applications designed especially which enable user interaction with other applications. Edgar F. Codd proposed the relational model in
Paradoxically the main reason behind the popularity of NoSQL data stores is the fact that their lack of ability to do advanced queries joins, groupings, ranking and analytics that allows these data stores to be scaled much, much easier than any RDBMS, which is a very valuable feature in todays world of massively distributed systems. Follow along and refresh your knowledge about 25 top most advanced NoSQL Interview Questions and Answers you should learn for your next developer interview in A NoSQL database provides a mechanism for storage and retrieval of data that is modeled in means other than the tabular relations used in relational databases like SQL, Oracle, etc. At the present time, the internet is loaded with big data, big users, big complexity etc. NoSQL is a type of database that can handle and sort all type of unstructured, messy and complicated data.
Answer: Name. Every relation in a relational database should have a name which is unique among all other relations. Each column in a relation is called an attribute. Each and every row in a relation is called a tuple. A tuple defines a collection of attribute values.
A database is an organized collection of data, stored and retrieved digitally from a remote or local computer system. Databases can be vast and complex, and such databases are developed using fixed design and modeling approaches. DBMS is a system software responsible for the creation, retrieval, updation and management of the database. It ensures that our data is consistent, organized and is easily accessible by serving as an interface between the database and its end users or application softwares. The key difference here, compared to DBMS, is that RDBMS stores data in the form of a collection of tables and relations can be defined between the common fields of these tables.
Стратмор покачал головой: - Больше никто не знает о существовании кольца. Именно поэтому я и послал за ним Дэвида. Я хотел, чтобы никто ничего не заподозрил. Любопытным шпикам не придет в голову сесть на хвост преподавателю испанского языка. - Он профессор, - поправила его Сьюзан и тут же пожалела об .
Наконец Беккер дошел до конца темного коридора и толкнул чуть приоткрытую дверь слева. Комната была пуста, если не считать старой изможденной женщины на койке, пытавшейся подсунуть под себя судно. Хорошенькое зрелище, - подумал Беккер. - Где, черт возьми, регистратура. За едва заметным изгибом коридора Беккер услышал голоса.
Она пожала плечами: - Быть может, Стратмору не хотелось задерживаться здесь вчера вечером для подготовки отчета. Он же знал, что Фонтейн в отъезде, и решил уйти пораньше и отправиться на рыбалку.
В Космополитене пишут, что две трети просьб потереть спинку кончаются сексом. Бринкерхофф возмутился. - У нас ничего такого не случалось. - Вот. - Она едва заметно подмигнула.
Шифровалка исчезла. ГЛАВА 57 В туалетных комнатах шифровалки не было окон, и Сьюзан Флетчер оказалась в полной темноте. Она замерла, стараясь успокоиться и чувствуя, как растущая паника сковывает ее тело. Душераздирающий крик, раздавшийся из вентиляционной шахты, все еще звучал в ее ушах. Вопреки отчаянным попыткам подавить охвативший ее страх Сьюзан явственно ощущала, что это чувство завладевает ею безраздельно.
Еще немного, - повторяла она мысленно. - Северная Дакота - это Хейл.
Дэвид посмотрел ей в глаза: - Ты выйдешь за меня замуж. У нее перехватило дыхание. Она посмотрела на него, потом на кольцо. Глаза ее увлажнились. - О, Дэвид… у меня нет слов.
У вас есть кое-что, что мне очень нужно, - сказал Беккер. - Да-да, конечно, - быстро проговорил немец, натужно улыбаясь. Он подошел к туалетному столику, где лежал бумажник. - Сколько. Беккер изобразил крайнюю степень негодования.
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