30+ SQL Developer Interview Questions and Answers for Freshers

SQL is a programming language used to manage and manipulate relational databases.

• SQL stands for Structured Query Language

• SQL commands are used to create, modify, and query databases

• SQL functions are used to perform calculations and manipulate data

• Special operators include LIKE, IN, BETWEEN, and NULL

• Examples of SQL commands include SELECT, INSERT, UPDATE, and DELETE

A stored procedure is a prepared SQL code that can be saved and reused.

• Stored procedures are used to perform a specific task or set of tasks in a database.

• They can accept input parameters and return output parameters.

• Stored procedures can improve performance by reducing network traffic and improving security.

• Examples: sp_GetCustomerDetails, sp_InsertEmployee

Different types of joins include inner join, outer join, left join, and right join. Self join is when a table is joined with itself.

• Inner join: Returns rows when there is a match in both tables

• Outer join: Returns all rows when there is a match in one of the tables

• Left join: Returns all rows from the left table and the matched rows from the right table

• Right join: Returns all rows from the right table and the matched rows from the left table

• Self join: Joining a table with itsel...read more

Oracle database is a proprietary database management system while ANSI is a standard for SQL language.

• Oracle database is developed and owned by Oracle Corporation while ANSI is a standard for SQL language developed by American National Standards Institute.

• Oracle database has its own unique features and functions while ANSI SQL is a standard that ensures compatibility and portability of SQL code across different database systems.

• Oracle database supports PL/SQL programming lang...read more

Query to display nth highest salary in SQL

• Use the ORDER BY clause to sort salaries in descending order

• Use the DISTINCT keyword to eliminate duplicates

• Use the LIMIT clause to specify the nth highest salary

A database is a collection of organized data that can be easily accessed, managed, and updated. Data is any information that can be stored and processed.

• A database is a software system that stores and manages data

• Data is any information that can be stored and processed, such as text, numbers, images, and videos

• Examples of databases include MySQL, Oracle, and SQL Server

• Examples of data include customer names, addresses, and purchase history

A view is a virtual table created by a query. It can be used to simplify complex queries, provide security, and improve performance.

• Views can hide complexity by encapsulating multiple tables into a single virtual table.

• Views can restrict access to certain columns or rows, providing security.

• Views can improve performance by pre-computing joins or aggregations.

• Example: CREATE VIEW vw_employee AS SELECT emp_id, emp_name FROM employees WHERE emp_dept = 'IT';

Web development using JavaScript and Python involves using both languages to create dynamic and interactive websites.

• JavaScript is used for client-side scripting to make web pages interactive.

• Python can be used for server-side scripting to handle backend logic and data processing.

• Both languages can be used together in a full-stack web development project.

• Examples: Using JavaScript for front-end validation and Python for backend API development.

Updating customer table

• Use UPDATE statement with SET clause to update table

• Specify the column to be updated and the new value

• Use WHERE clause to specify the condition for updating specific rows

Creating a table and inserting values in SQL.

• Use CREATE TABLE statement to create a table.

• Use INSERT INTO statement to insert values into the table.

• Specify column names and data types when creating the table.

• Provide values for each column when inserting data into the table.

Java programming involving manipulation of strings

• Use String class methods like substring, indexOf, replace, etc.

• String concatenation using '+' operator

• String comparison using equals() method

• Regular expressions for advanced string manipulation

Optimizing SQL queries involves using indexes, minimizing data retrieval, and avoiding unnecessary joins.

• Use indexes on columns frequently used in WHERE clauses

• Minimize data retrieval by selecting only necessary columns

• Avoid unnecessary joins by using subqueries or temporary tables

Creating customer table in SQL

• Define the table structure with appropriate data types for each column

• Include columns for customer ID, name, address, email, phone number, etc.

• Set appropriate constraints such as primary key, unique, not null, etc.

• Consider adding additional columns for date of birth, gender, etc. if required

• Create indexes on frequently queried columns for better performance

SQL triggers are special stored procedures that are automatically executed when certain events occur in a database.

• Triggers are used to enforce business rules, maintain referential integrity, and automate repetitive tasks.

• They can be defined to execute before or after INSERT, UPDATE, or DELETE operations on a table.

• For example, a trigger can be created to update a log table whenever a new record is inserted into a main table.

To input values in MySQL, use the INSERT INTO statement with the table name and column names.

• Use INSERT INTO statement followed by the table name

• Specify the column names in parentheses after the table name

• Provide the values to be inserted in the corresponding order

To delete customer table in SQL, use the DROP TABLE command.

• Use the DROP TABLE command followed by the table name.

• Make sure to backup the data before deleting the table.

• Ensure that there are no dependencies on the table before deleting it.

Ci/cd pipeline automates the process of building, testing, and deploying code changes.

• Automates code integration, testing, and deployment

• Ensures consistency and reliability in software delivery

• Facilitates faster feedback loops for developers

• Examples: Jenkins, GitLab CI/CD, Azure DevOps

Explanation of delete, truncate and joins in SQL

• DELETE statement removes specific rows from a table

• TRUNCATE statement removes all rows from a table

• JOIN statement combines rows from two or more tables based on a related column

• INNER JOIN returns only matching rows from both tables

• LEFT JOIN returns all rows from the left table and matching rows from the right table

• RIGHT JOIN returns all rows from the right table and matching rows from the left table

• FULL OUTER JOIN returns all ro...read more

To write a query, you need to use SQL syntax to retrieve specific data from a database.

• Start with the SELECT statement to specify the columns you want to retrieve

• Use the FROM clause to specify the table(s) you want to query

• Add conditions using the WHERE clause to filter the data

• Use JOIN clauses to combine data from multiple tables

• Group and aggregate data using the GROUP BY and HAVING clauses

• Sort the results using the ORDER BY clause

Cursors are used to retrieve data from a result set one row at a time.

• Cursors are used when we need to perform operations on individual rows of a result set.

• They are declared, opened, fetched, and closed.

• They can be used to update or delete data in a table.

• They can be slow and memory-intensive, so should be used sparingly.

• Example: DECLARE cursor_name CURSOR FOR SELECT * FROM table_name;

• Example: OPEN cursor_name; FETCH NEXT FROM cursor_name INTO @variable;

• Example: CLOSE cursor...read more

Joins are used to combine data from two or more tables based on a related column.

• Types of joins: inner, left, right, full outer

• Syntax: SELECT * FROM table1 JOIN table2 ON table1.column = table2.column

• Can also use aliases for table names and columns

• Joins can be nested or chained together

Triggers are special types of stored procedures that are automatically executed in response to certain events.

• Triggers are used to enforce business rules or to perform complex calculations that involve multiple tables.

• They can be used to audit changes to data, or to replicate data across multiple tables.

• Triggers can be defined to execute before or after an INSERT, UPDATE, or DELETE statement.

• They can also be defined to execute instead of the triggering statement.

• Triggers can ...read more

Use the GETDATE() function in SQL to find today's date.

• Use the GETDATE() function in SQL to get the current date and time

• To get only the date part, use the CONVERT function with the appropriate style code

• Example: SELECT CONVERT(date, GETDATE()) AS TodayDate;

Indexes are used to improve the performance of SQL queries by reducing the time taken to retrieve data.

• Indexes are created on one or more columns of a table.

• They can be clustered or non-clustered.

• Clustered indexes determine the physical order of data in a table.

• Non-clustered indexes create a separate structure to hold the indexed data.

• Indexes should be used judiciously as they can slow down data modification operations.

Normalization is the process of organizing data in a database to reduce redundancy and improve data integrity.

• Normalization involves breaking down a table into smaller tables and defining relationships between them.

• There are different levels of normalization, with each level having specific rules to follow.

• Normalization helps to prevent data inconsistencies and anomalies.

• Example: A customer table can be normalized into a customer table and an order table, with a relationship ...read more

Subsets of SQL are different types of SQL languages used for specific purposes.

• Data Definition Language (DDL) - used to define database schema

• Data Manipulation Language (DML) - used to manipulate data in database

• Data Control Language (DCL) - used to control access to database

• Transaction Control Language (TCL) - used to manage transactions

• Examples: CREATE, SELECT, INSERT, UPDATE, DELETE, GRANT, REVOKE, COMMIT, ROLLBACK

Types of joins in SQL are Inner Join, Left Join, Right Join, Full Outer Join, Cross Join.

• Inner Join returns only the matching rows from both tables.

• Left Join returns all the rows from the left table and matching rows from the right table.

• Right Join returns all the rows from the right table and matching rows from the left table.

• Full Outer Join returns all the rows from both tables.

• Cross Join returns the Cartesian product of both tables.