200+ SQL Developer Interview Questions and Answers

A change request in an application is serviced by the development team through various stages such as business analysis, code analysis, discussion with BA, and requirement freeze.

• The development team starts by analyzing the change request to understand its impact on the application.

• They perform business analysis to determine the feasibility and potential risks of implementing the change.

• Code analysis is conducted to assess the impact on existing code and identify any necessar...read more

Procedure to return a series (99, 96, 93, ...., 6, 3)

• Create a temporary table with a single column

• Use a loop to insert values into the temporary table

• Return the values from the temporary table in descending order

The result sets of all types of joins in SQL

• Inner Join: Returns only the matching rows from both tables

• Left Join: Returns all the rows from the left table and the matching rows from the right table

• Right Join: Returns all the rows from the right table and the matching rows from the left table

• Full Outer Join: Returns all the rows from both tables, including the unmatched rows

• Cross Join: Returns the Cartesian product of both tables

Query optimization techniques and types of schemas

• Query optimization techniques include indexing, query rewriting, and partitioning

• Schemas include user-defined, system-defined, and temporary schemas

• User-defined schemas are created by users to organize database objects

• System-defined schemas are created by the database management system

• Temporary schemas are used for temporary storage of data

• Differences between schemas include ownership, accessibility, and visibility

Use SQL JOIN to combine two tables and display information.

• Use the JOIN keyword to combine tables based on a related column

• Specify the columns you want to display in the SELECT statement

• Use ON clause to specify the column used for joining the tables

To delete records in a table, use the DELETE statement with the WHERE clause to specify the condition for deletion.

• Use the DELETE statement followed by the table name

• Add the WHERE clause to specify the condition for deletion

• Execute the query to delete the records

I have 5 years of experience in SQL. My last project involved optimizing database queries for a large e-commerce platform.

• 5 years of experience in SQL

• Optimized database queries for a large e-commerce platform

• Worked on improving performance and efficiency of database operations

Functions and procedures are both stored database objects used to perform specific tasks in SQL.

• Functions return a value while procedures do not.

• Functions can be used in SQL statements, whereas procedures cannot.

• Functions can have input parameters and return a single value, while procedures can have input and output parameters.

• Functions are typically used for calculations or data manipulation, while procedures are used for executing a series of SQL statements.

• Examples of func...read more

SQL is a programming language used for managing and manipulating relational databases.

• SQL stands for Structured Query Language.

• It is used to communicate with and manipulate databases.

• SQL can be used to create, modify, and retrieve data from databases.

• It is a standard language for relational database management systems (RDBMS).

Job security in Avendata Gmbh is good.

• Avendata Gmbh has a stable and growing business.

• The company has a diverse range of clients and projects.

• Avendata Gmbh invests in employee training and development.

• The company has a positive work culture and values its employees.

• There have been no recent reports of layoffs or downsizing.

SQL is a standard language for managing databases, while MySQL is a specific open-source relational database management system.

• SQL is a standard language used to manage databases, while MySQL is a specific implementation of SQL.

• SQL is an ANSI (American National Standards Institute) standard, while MySQL is an open-source relational database management system.

• SQL can be used with various database management systems like Oracle, SQL Server, etc., while MySQL is a specific datab...read more

Delete command is used to remove specific rows from a table, while truncate command is used to remove all rows from a table.

• Delete command is a DML (Data Manipulation Language) statement.

• Delete command can be used with a WHERE clause to specify the rows to be deleted.

• Truncate command is a DDL (Data Definition Language) statement.

• Truncate command removes all rows from a table, but keeps the table structure intact.

• Truncate command is faster than delete command as it does not ge...read more

Views are virtual tables that display data from one or more tables, while stored procedures are a set of SQL statements that perform a specific task.

• Views are used to simplify complex queries by storing them as a virtual table.

• Views do not store data themselves, but rather display data from underlying tables.

• Stored procedures are precompiled sets of SQL statements that can be executed with parameters.

• Stored procedures can perform tasks such as data manipulation, validation, a...read more

Print numbers in pyramid shape patterns using SQL code.

• Use a loop to iterate through rows and columns to print the numbers in pyramid shape.

• Increment the numbers in each row to create the pyramid effect.

• Consider the spacing and alignment to create a visually appealing pyramid pattern.

SQL is a programming language used for managing data in relational databases. Window functions are used for calculations within a specific window of rows. Joins are used to combine data from multiple tables based on a related column.

• SQL stands for Structured Query Language and is used for managing data in relational databases

• Window functions in SQL allow for calculations to be performed within a specific window of rows

• Examples of window functions include ROW_NUMBER(), RANK(),...read more

In MS SQL Server, concatenation is done using the + symbol.

• MS SQL Server does not have a CONCAT function

• Use the + symbol to concatenate strings

• Example: SELECT 'Hello' + ' ' + 'World' AS Greeting

Rank and Dense_Rank are window functions used to assign a rank to each row based on a specific column value.

• Rank assigns unique ranks to each row based on the column value.

• Dense_Rank assigns ranks to each row based on the column value, but skips the rank if there are ties.

• Both functions are used with the OVER() clause and ORDER BY statement.

• Example: SELECT name, salary, RANK() OVER(ORDER BY salary DESC) AS rank FROM employees;

• Example: SELECT name, salary, DENSE_RANK() OVER(OR...read more

Join is used to combine rows from two or more tables based on a related column between them.

• Join is used to retrieve data from multiple tables.

• Syntax: SELECT column_name(s) FROM table1 JOIN table2 ON table1.column_name = table2.column_name;

• Types of joins: INNER JOIN, LEFT JOIN, RIGHT JOIN, FULL OUTER JOIN, CROSS JOIN.

• Example: SELECT customers.name, orders.order_date FROM customers JOIN orders ON customers.customer_id = orders.customer_id;

Dense Rank and Rank are SQL functions used to assign a rank to each row in a result set based on a specified criteria.

• Dense Rank assigns unique ranks to each row, leaving no gaps in the ranking sequence.

• Rank assigns ranks to each row, leaving gaps in the ranking sequence.

• Both functions can be used with the OVER clause to partition the result set and order the ranking based on specific columns.

• Dense Rank and Rank are commonly used in scenarios like leaderboard rankings, top N ...read more

List is a collection of objects, string array is an array of strings, etc. Each has its own characteristics and uses.

• List: dynamic collection of objects, can grow/shrink in size. Example: List numbers = new ArrayList<>();

• String array: fixed-size array containing strings. Example: String[] names = new String[3];

• Array: fixed-size collection of elements of the same type. Example: int[] scores = new int[5];

AS is used to assign an alias to a column or table in SQL, while IS is used to compare values or check for null values.

• AS is used in SELECT statements to assign a temporary name to a column or table

• AS can also be used in JOIN statements to assign aliases to tables

• IS is used in WHERE clauses to compare values or check for null values

• IS NULL is used to check if a value is null

• IS NOT NULL is used to check if a value is not null

Primary key uniquely identifies each record in a table, while unique key ensures each value in a column is unique.

• Primary key does not allow NULL values, while unique key allows one NULL value.

• A table can have only one primary key, but multiple unique keys.

• Primary key automatically creates a unique index, while unique key does not.

• Primary key is used to establish relationships between tables, while unique key is used to enforce data integrity.

To get the highest salary by grouping department, use SQL queries with GROUP BY and ORDER BY clauses.

• Use GROUP BY clause to group the data by department.

• Use MAX() function to find the highest salary within each department.

• Use ORDER BY clause to sort the results in descending order of salary.

• Example: SELECT department, MAX(salary) AS highest_salary FROM employees GROUP BY department ORDER BY highest_salary DESC;

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

Temporary tables are stored in tempdb while table variables are stored in memory.

• Temporary tables are created using CREATE TABLE statement while table variables are declared using DECLARE statement.

• Temporary tables can be accessed across sessions while table variables are limited to the scope of the batch, stored procedure or function.

• Temporary tables can have indexes and constraints while table variables cannot.

• Temporary tables can be dropped explicitly while table variables...read more

SQL code to find Nth maximum salary department wise.

• Use the RANK() function to assign a rank to each salary within each department.

• Filter the results to only include the rows where the rank is equal to N.

• Group the results by department to get the Nth maximum salary department wise.

To delete rows from 3 tables with a single query, use the DELETE statement with JOINs.

• Use the DELETE statement with JOINs to specify the tables and conditions for deletion.

• Ensure that the JOIN conditions are properly defined to delete the desired rows.

• Use aliases for table names to simplify the query and improve readability.

• Test the query with a SELECT statement before executing the DELETE statement to verify the rows to be deleted.

The leave policy is comprehensive and employee-friendly.

• Employees are entitled to a certain number of paid leave days per year.

• Additional leave can be taken for special circumstances like maternity/paternity leave or bereavement leave.

• Leave can be requested and approved through an online system or by submitting a form to the HR department.

• Unused leave days can sometimes be carried forward to the next year or compensated monetarily.

• The policy may vary based on the employee's t...read more

Code to sort array without sort function

• Iterate through the array and compare each element with the rest to find the smallest element

• Swap the smallest element with the first element in the unsorted portion of the array

• Repeat the process for the remaining unsorted portion of the array until fully sorted

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

• Types of joins include inner join, left join, right join, and full outer join.

• Inner join returns only the 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 rows from both tables, with NULL values for non-matching rows...read more

Use SELECT DISTINCT statement to find unique values in a table.

• Use SELECT DISTINCT column_name FROM table_name

• DISTINCT keyword returns only unique values

• Can be used with multiple columns

• Can be combined with other SQL statements like WHERE and ORDER BY

Use DATEDIFF function to calculate total experience from DOJ

• Use DATEDIFF function to calculate the difference between current date and DOJ

• Convert the result into years, months, and days format

• Consider leap years and varying month lengths in the calculation

Functions return a value while Stored Procedures do not.

• Functions are used to perform a specific task and return a value.

• Stored Procedures are used to perform a set of operations and do not return a value.

• Functions can be used in SELECT, WHERE, and HAVING clauses.

• Stored Procedures can be used to modify data, but not return it.

• Functions can be called from Stored Procedures.

• Stored Procedures can call Functions.

To extract execution plan of a SQL query, use EXPLAIN or SHOW PLAN command.

• Use EXPLAIN or SHOW PLAN command before the SQL query

• EXPLAIN command shows the execution plan in a tabular format

• SHOW PLAN command shows the execution plan in a graphical format

• Execution plan helps in optimizing the query for better performance

SQL is a programming language used for managing data in relational databases. Different types of joins include inner, outer, left, right, and full. Types of subqueries include correlated and non-correlated subqueries.

• SQL is a language used for managing data in relational databases

• Types of joins include inner, outer, left, right, and full

• Types of subqueries include correlated and non-correlated subqueries

PIVOT and UNPIVOT are used to transform data from rows to columns and vice versa.

• PIVOT is used to rotate rows into columns

• UNPIVOT is used to rotate columns into rows

• PIVOT requires an aggregate function to be specified

• UNPIVOT requires the column names to be specified

• PIVOT and UNPIVOT are used in T-SQL

• Example: PIVOT (SUM(Sales) FOR Product IN ([A], [B], [C]))

• Example: UNPIVOT (Sales FOR Product IN ([A], [B], [C]))

A primary key is a unique identifier for a record in a database table.

• A primary key must be unique and not null.

• It ensures the uniqueness and integrity of data in a table.

• Primary keys are used to establish relationships between tables.

• Examples of primary keys include social security numbers, email addresses, or auto-incremented IDs.

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

• Types of joins include INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN

• INNER JOIN returns rows when there is at least one match in both 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

• FULL JOIN returns rows when there is a match in one of the tables

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

Constrain is a rule that restricts the values in a database column. DDL is a set of SQL commands used to create, modify, and delete database objects.

• Constrains ensure data integrity and prevent invalid data from being inserted into a database.

• DDL includes commands like CREATE, ALTER, and DROP to manage database objects like tables, indexes, and views.

• Constrains are defined using DDL commands like CHECK, UNIQUE, and FOREIGN KEY.

• DDL is used to define the structure of a database...read more

Object-oriented programming concepts that focus on classes, objects, inheritance, encapsulation, and polymorphism.

• Classes: Blueprint for creating objects with attributes and methods.

• Objects: Instances of classes that contain data and behavior.

• Inheritance: Ability for a class to inherit attributes and methods from another class.

• Encapsulation: Bundling data and methods that operate on the data into a single unit.

• Polymorphism: Ability for objects of different classes to respond ...read more

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

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

• Normalization helps to eliminate data inconsistencies and anomalies.

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

• For example, first normal form (1NF) requires that each column in a table contain atomic values.

• Second normal ...read more

To troubleshoot a stored procedure, check for syntax errors, run the procedure with test data, and use debugging tools.

• Check for syntax errors in the stored procedure code

• Run the procedure with test data to identify any logical errors

• Use debugging tools like SQL Server Profiler or Visual Studio Debugger to step through the code and identify issues

• Check for any database connectivity issues or permission errors

• Review the error logs and event viewer for any related errors

SQL is a language used to manage data in relational databases. It has different types of statements to manipulate data.

• SQL has Data Definition Language (DDL) statements to create, modify, and delete database objects.

• SQL has Data Manipulation Language (DML) statements to insert, update, and delete data in tables.

• SQL has Data Control Language (DCL) statements to grant or revoke access to database objects.

• SQL has Transaction Control Language (TCL) statements to manage transactio...read more

SET NOCOUNT ON is a T-SQL statement that stops the message indicating the number of rows affected by a Transact-SQL statement.

• SET NOCOUNT ON is used to improve the performance of stored procedures by reducing network traffic.

• It is particularly useful when executing large scripts or batch processes.

• It is also used to suppress the '(X row(s) affected)' message in SQL Server Management Studio.

• To turn it off, use SET NOCOUNT OFF.

Temp tables are physical tables stored in tempdb, while table variables are in-memory structures.

• Temp tables are stored in tempdb database, while table variables are created in memory.

• Temp tables can be indexed and have statistics, while table variables cannot.

• Temp tables can be used across multiple sessions, while table variables are limited to the current session.

• Temp tables support DDL operations like ALTER TABLE, while table variables do not.

• Temp tables are generally pref...read more

An index is a database object that improves the speed of data retrieval operations on a table.

• Indexes are created on columns of a table.

• Creating an index involves specifying the table name, column name, and index type.

• Types of indexes include clustered, non-clustered, unique, and full-text indexes.