Below are provided some of the critical SQL interview questions and answers. Through this, you will be one step forward for the interview. Let’s now dive into the SQL interview questions:
Top SQL Interview Questions
- What is Database?
The organized form of data that helps us with quick access, collecting, and storing data is known as the Database. The Database is also called the form of structured information that is accessed in various ways. An example of a Database is School and Bank Management Database.
- Difference between DBMS and RDBMS?
|Database Management System||Relational Database Management System|
|Data is stored as a file.The data is stored in two different forms either the hierarchical or the navigational form.Normalization is not present.The distributed database is not supported.Examples:File SystemsXML etc.||Data is stored in tabular form.The table contains an identifier known as the primary key. Hence, they are stored as tables.Normalization is present.Supports the distributed Database.Examples:MySQLSQL Server, etc.|
- What is a primary key?
A primary key is a mix of fields that exceptionally determine a column. This is an extraordinary sort of uncommon key, and it has understood the NOT NULL requirement. The values of the Primary key can’t be NULL.
- What is a unique key?
A Unique key limitation mainly recognized each record in the data set. This gives uniqueness to the section or group of segments.
One of the most important question in the SQL Interview Questions
- How is a unique key different from a primary key?
A Primary key limitation has programmed extraordinary imperative characterized on it. Yet, not, on account of Unique Key.
There are numerous unique constraints characterized per table; however, only one Primary key imperative is described per table.
- What is a foreign key?
A foreign key is one table that is identified with the essential key of another table. The relationship is made between two tables by referring to the foreign key with another table’s crucial key.
- What is a join?
This is a keyword used for the query data from more tables dependent on the connection between the fields of the tables. Keys assume a significant part when JOINs are utilized.
Intermediate SQL Interview Questions
- What are the constraints in SQL?
Some limitations specify the protocols concerning each data in a table. These limitations are known as the Constraints in SQL. Constraints are applied either to the single or multiple fields of the tables in SQL. Constraints check the data either during the creation of the table or after the table’s design using the ALTER TABLE Command. Given below is the list of some common constraints in SQL:
- Default: When an automated default value is provided to an empty field.
- Check: Where all the values satisfy the given condition.
- Unique: When all the values are different.
- Foreign Key: Identifies all the values.
- Primary Key: Makes sure that there is referential integrity in a different table.
- Index: Provides quicker retrievals of data.
- Not Null: All NULL value is restricted from being inserted.
- What are the different types of SQL Join?
- What is Data Integrity?
Data Integrity is the affirmation of exactness and consistency of information over its whole life cycle. It is crucial to the plan, implementation, and utilization of any framework that stores, measures, or recovers data. It also characterizes integrity constraints to implement business rules on the information when it is gone into an application or a database.
- What is a Query?
A query is an appeal for information or data from a database table or multiple tables. An information base question can be either a select query or an activity query.
- What are the uses of SQL?
Following are some of the usages of SQL:
- Responsible for organizing data structures and relational Database that are present in the Database.
- Update data in the Database
- Delete the unwanted data
- Create new databases
- Perform complex operations
- Creates view in the Database
- Insert new data
- Retrieve data from the Database.
Advanced SQL Interview Questions.
- What are the subsets of SQL?
There are three subsets in SQL, and they are:
- DDL: Data Definition Language is used when the data structure like CREATE, DROP, etc., are defined.
- DML: Data Manipulation Language is used when there is a need of manipulating the existing data in the Database. SELECT, INSERT, etc., are some of the commands of this category.
- DCL: Data Control Language is used when control access is given to the data using the commands like GRANT or Revoke.
- Distinguish between SQL and MySQL?
|The Microsoft Corporation||develops SQL.The Oracle Corporation develops MySQL.|
|SQL is not an open-source software||MySQL is an open-source software|
|SQL supports only the primary programming languages like C++, Python.||Along with the primary programming languages, MySQL also supports languages like Perl, Tcl, etc.|
|SQL gives high security; data can’t be manipulated.||MySQL gives lesser security as compared to SQL, as it supports data manipulation.|
|The server of SQL does not block during the time of backup.||The developer of MySQL needs to extract the data from the Database for data backup.|
- What is the difference between CHAR and VARCHAR?
|It is used when the character string is stored for a fixed length.||VARCHAR is used when the character string is stored for a variable length.|
|CHAR means “Character.”||VARCHAR means “Variable Character.”|
|The length of the string is lesser as compared to the set or fixed size so that it can be padded for extra memory space.||The length of the string is lesser as compared to the set or fixed length; however, it will be stored as it is without being padded for extra memory space.|
|Better performance than VARCHAR||Performance is not good as CHAR|
|CHAR takes 1 byte for each character.||VARCHAR also takes 1 byte for every character. Also, some extra bytes for length information.|
|Code Snippet:||Code Snippet:|
- Distinguish between the DELETE and TRUNCATE statements?
|DELETE statement||TRUNCATE statement|
|It is used as the indexed views.||Truncate does not contain such utility.|
|Permission is required to use the Delete statement.||ALTER permission is required when using the Truncate statement.|
|DELETE is a Data Manipulation Language command.||TRUNCATE is a Data Definition Language command.|
|It is used to omit specific rows.||It clears out all the rows in the table.|
|While trying to remove a tuple, it gets locked.||While trying to remove the table data, the data page gets locked.|
- What is a trigger?
Triggers are programs that are stored and help to get consequently executed when an occasion of statements like INSERT, DELETE, UPDATE(DML) happens. Triggers can also be evoked because of Data Definition Language(DDL) and database operations, like SERVER ERROR, LOGON.
- What are the UNION, MINUS and INTERSECT orders?
The UNION administrator joins and returns the outcome set recovered by at least two SELECT proclamations.
The MINUS administrator in SQL is utilized to eliminate copies from the outcome set got a continuously SELECT question from the outcome set acquired by the principal SELECT inquiry. Afterwards, return the sifted results from the first.
The INTERSECT provision in SQL joins the outcome set brought by the two SELECT explanations where records from one match the other and afterwards returns this convergence of result-sets.
Certain conditions should be met while executing both of the above statements in SQL –
- Every SELECT statement within the clause should have a similar number of segments.
- The segments need to have similar data types.
- The segments in each SELECT statement are required to have a similar order fundamentally.
- State all the different relationships in SQL?
The different relationships in SQL are given as follows:
- One-to-One: This can be characterized as the connection between two tables where each record in one table is related to the limit of one record in the other table.
- One-to-Many and Many-to-One: This is the most regularly utilized relationship where a record in a table is related to various records in the other table.
- Many-to-Many: This is utilized in situations when various cases on the two sides are required for characterizing a relationship.
- Self-Referencing Relationships: This is utilized when a table requirement to characterize a relationship with itself.
- State the different operators used in SQL?
There are usually three types of operators that are used in SQL. They are as follows:
- Arithmetic Operators
- Comparison Operators
- Logical Operators
- What is the subquery in SQL?
A subquery is the type of query which contains another query within, and the query is used to retrieve information from the Database. The outer query of the subquery is known as the main query, and the inner query of the subquery is called the subquery.
We are at the end of the blog on the top SQL Interview Questions. To get the complete details on the topics, check out our Free Course on SQL Interview Questions at Great Learning Academy. We hope that you are now better equipped to attend the upcoming sessions. Good luck and happy learning!