File Name: relational database interview questions and answers .zip
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.
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. Learn from it and ace your SQL interview! This is a one-stop resource through which you can avail the maximum benefit and prepare for job interviews easily.
Check out the top SQL interview questions asked by recruiters today:. What is SQL? Explain the different types of SQL commands. What is a default constraint? What is a unique constraint? How would you find the second highest salary from the below table?
What is a Primary Key? What is a Foreign Key? What is an Index? Explain the types of Indexes. Basically, it is a database language that is used for the creation and deletion of databases, and it can be used to fetch and modify the rows of a table and also for multiple other things. Constraints are used to specify some sort of rules for processing data and limiting the type of data that can go into a table.
Default constraint : It is used to define a default value for a column so that the default value will be added to all the new records if no other value is specified. We will start off by creating a new table and adding a default constraint to one of its columns. Unique constraints ensure that all the values in a column are different. Code :. A primary key is used to uniquely identify all table records. It cannot have NULL values, and it must contain unique values. A table can have only one primary key that consists of single or multiple fields.
A foreign key is an attribute or a set of attributes that references to the primary key of some other table. So, basically, it is used to link together two tables. Indexes help speed up searching in the database. If there is no index on any column in the WHERE clause, then the SQL server has to skim through the entire table and check each and every row to find matches, which might result in slow operation on large data.
Indexes are used to find all rows matching with some columns and then to skim through only those subsets of the data to find the matches. Single-column Indexes : A single-column index is created for only one column of a table. Composite-column Indexes : A composite-column index is an index created for two or more columns of the table. Unique Indexes : Unique indexes are used for maintaining the data integrity of the table. Clustered index : It is used to sort the rows of data by their key values.
A clustered index is like the contents of a phone book. Since the data is located next to each other, it helps a lot in fetching data based on range-based queries. Also, the clustered index is actually related to how the data is stored. There is only one clustered index possible per table. Non-clustered index : It stores data at one location and indexes at some other location. The index has pointers that point to the location of the data. As the index in the non-clustered index is stored in different places, there can be many non-clustered indexes for a table.
It is a programming language for a database that uses SQL. SQL is a declarative and data-oriented language. It is mainly used for the manipulation of data. It is used for creating an application. It provides interaction with the database server. It does not provide interaction with the database server.
Normalization is used in reducing data redundancy and dependency by organizing fields and tables in databases. It involves constructing tables and setting up relationships between those tables according to certain rules.
The redundancy and inconsistent dependency can be removed using these rules to make it more flexible. Denormalization is contrary to normalization. In this, we basically add redundant data to speed up complex queries involving multiple tables to join. Here, we attempt to optimize the read performance of a database by adding redundant data or by grouping the data.
The stuff function deletes a part of the string and then inserts another part into the string starting at a specified position. Here, String1 is the one that would be overwritten. Position indicates the starting location for overwriting the string. Length is the length of the substitute string, and String2 is the string that would overwrite String1. Views are virtual tables used to limit the tables that we want to display, and these are nothing but the result of a SQL statement that has a name associated with it.
Since views are not virtually present, they take less space to store. We can create a view-only table for the female employees from the entire employee table. A stored procedure is a prepared SQL code that can be saved and reused. In other words, we can consider a stored procedure to be a function consisting of many SQL statements to access the database system. We can consolidate several SQL statements into a stored procedure and execute them whenever and wherever required.
A stored procedure can be used as a means of modular programming, i. This also supports faster execution when compared to executing multiple queries. The Join clause is used to combine rows from two or more tables based on a related column between them. There are various types of Joins that can be used to retrieve data, and it depends upon the relationship between tables. Right Join: Right Join returns rows that are common between the tables and all the rows of the right-hand-side table, i.
Full Join: Full Join returns all the rows from the left-hand-side table and all the rows from the right-hand-side table. Let us suppose, we have two tables Table A and Table B. When we apply Inner Join on these two tables, we will get only those records that are common to both Table A and Table B. Output :. After Inner Join, we have only those records where the departments match in both tables.
As we can see, the matched departments are Support, Analytics, and Sales. Views Tables It is a virtual table that is extracted from a database. A table is structured with a set number of columns and a boundless number of rows. Views do not hold data themselves. Table contains data and stores the data in databases.
A view is also utilized to query certain information contained in a few distinct tables. A table holds fundamental client information and the cases of a characterized object. In a view, we will get frequently queried information. In a table, changing the information in the database changes the information that appears in the view.
A temporary table helps us store and process intermediate results. These temporary tables are created and can be automatically deleted when they are no longer used.
They are very useful in places where we need to store temporary data. One of the important attributes of the OLTP system is its potentiality to keep up the consistency. The OLTP system often follows decentralized planning to keep away from single points of failure. This system is generally designed for a large audience of end-users to perform short transactions. Also, queries involved in such databases are generally simple, need fast response time, and in comparison, it returns only a few records.
So, the number of transactions per second acts as an effective measure for those systems. For OLAP systems, the efficacy computing depends highly on the response time. Hence, such systems are generally used for data mining or maintaining aggregated historical data, and they are usually used in multi-dimensional schemas.
Self Join in SQL is used for joining a table with itself. Here, depending upon some conditions, each row of the table is joined with itself and with other rows of the table. The Union operator is used to combine the result set of two or more select statements. For example, the first select statement returns the fish shown in Image A, and the second returns the fish shown in Image B. Then, the Union operator will return the result of the two select statements as shown in Image A U B.
Also, if there is a record present in both tables, then we will get only one of them in the final result.
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 A database language may also incorporate features like: DBMS-specific Configuration and management of storage engine Computations to modification of query results by computations, like summing, counting, averaging, grouping, sorting and cross-referencing Constraint enforcement Application Programming Interface 7 What do database languages do?
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.
Most popular commercial and open source databases currently in use are based on the relational model.
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.
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. What is DBMS? DBMS can be termed as File Manager that manages data in a database rather than saving it in file systems.
questions. SQL Interview Questions PDF file: Download here RDBMS stands for Relational Database Management System. RDBMS store.
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. It is the standard language for relational database management systems.
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