200+ SQL Developer Interview Questions and Answers

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.

I have used multiple functions in SSAS for various purposes.

• Some commonly used functions in SSAS include SUM, AVG, COUNT, MIN, MAX, and DISTINCT.

• Functions can be used in measures, calculated columns, and calculated tables.

• Examples of functions used in SSAS include SUM([Sales Amount]), COUNT([Customer ID]), and AVG([Rating]).

SQL Developer interview question on removing duplicates, finding third highest salary, normalization, and indexes.

• To remove duplicates, use the DISTINCT keyword or GROUP BY clause

• To find third highest salary, use the LIMIT keyword with OFFSET 2

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

• Indexes are used to improve query performance by creating a data structure that allows for faster data retrieval

• Drawbacks of in...read more

There are three types of commands in a database: DDL, DML, and DCL.

• DDL (Data Definition Language) commands are used to define the database structure, such as creating tables, altering tables, and dropping tables.

• DML (Data Manipulation Language) commands are used to manipulate data in the database, such as inserting, updating, and deleting data.

• DCL (Data Control Language) commands are used to control access to the database, such as granting and revoking privileges to users.

DBMS stands for Database Management System, which is a software system that allows users to define, create, maintain and control access to databases.

• DBMS is a software system that allows users to interact with databases.

• It helps in defining, creating, maintaining, and controlling access to databases.

• Examples of DBMS include MySQL, Oracle Database, Microsoft SQL Server.

DDL is Data Definition Language used to define database structure, while DML is Data Manipulation Language used to manage data within database.

• DDL is used to create, modify, and delete database objects like tables, indexes, etc.

• DML is used to insert, update, delete, and retrieve data from database tables.

• DDL statements include CREATE, ALTER, DROP, TRUNCATE, etc.

• DML statements include INSERT, UPDATE, DELETE, SELECT, etc.

SQL is a programming language used for managing data in relational databases. Functions are reusable code blocks. Joins combine data from multiple tables. LIKE operator is used for pattern matching.

• SQL is a language for managing data in databases

• Functions are reusable code blocks

• Joins combine data from multiple tables

• LIKE operator is used for pattern matching, e.g. SELECT * FROM table WHERE column LIKE '%keyword%'

SQL concepts - Procedure, Functions, Joins, Sub queries, Constraints, Triggers, Package

• Procedure - a set of SQL statements that perform a specific task

• Functions - a set of SQL statements that return a single value

• Joins - used to combine rows from two or more tables based on a related column

• Sub queries - a query within another query

• Constraints - rules that enforce data integrity

• Triggers - a set of SQL statements that automatically execute in response to certain events

• Package -...read more

Object-oriented programming concepts that help in organizing and structuring code.

• Encapsulation: Bundling data and methods together in a class.

• Inheritance: Creating new classes from existing ones, inheriting their properties and behaviors.

• Polymorphism: Ability of objects to take on many forms, allowing different classes to be used interchangeably.

• Abstraction: Hiding complex implementation details and providing a simplified interface.

• Encapsulation: Binding data and methods tog...read more

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

A set is a collection of unique values in SQL. Types of joins include inner, outer, left, right. Types of sets include union, intersect, except. WHERE is used for filtering rows, HAVING is used for filtering groups.

• Set is a collection of unique values in SQL

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

• Types of sets: union, intersect, except

• WHERE is used for filtering rows

• HAVING is used for filtering groups

The NVL() function is used to replace NULL values with a specified value.

• NVL() is commonly used in SQL queries to handle NULL values.

• It takes two arguments: the value to be checked and the replacement value.

• If the value is NULL, the function returns the replacement value.

• If the value is not NULL, the function returns the original value.

• Example: SELECT NVL(column_name, 'N/A') FROM table_name;

Functions return a value while stored procedures do not. Functions can be used in SQL statements, while stored procedures cannot.

• Functions return a single value, while stored procedures do not necessarily return any value.

• Functions can be used in SQL statements like SELECT, WHERE, etc., while stored procedures cannot be used in such statements.

• Functions are called using SELECT statement, while stored procedures are called using EXECUTE or EXEC statement.

• Functions cannot modif...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

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

Identity columns auto-generate values for new rows, while sequences are independent objects for generating unique numbers.

• Identity: Automatically generates a unique value for each new row in a table.

• Example: In SQL Server, you can define a column as 'IDENTITY(1,1)' to start at 1 and increment by 1.

• Sequence: A separate database object that generates a sequence of numeric values.

• Example: In Oracle, you can create a sequence using 'CREATE SEQUENCE seq_name START WITH 1 INCREMENT...read more

Set operators are used to combine the result sets of two or more SELECT statements.

• Set operators include UNION, UNION ALL, INTERSECT, and EXCEPT.

• UNION combines the results of two SELECT statements and removes duplicates.

• UNION ALL combines the results of two SELECT statements and includes duplicates.

• INTERSECT returns only the common rows between two SELECT statements.

• EXCEPT returns only the rows from the first SELECT statement that are not in the second SELECT statement.

Code to generate Fibonacci series

• Start with 0 and 1 as the first two numbers

• Add the previous two numbers to get the next number in the series

• Repeat until desired number of terms is reached

Synonyms are database objects that allow users to create aliases for other database objects.

• Synonyms can be used to simplify complex queries by providing a shorter name for a table or view.

• They can also be used to provide a layer of abstraction between the user and the underlying database objects.

• Synonyms can be created for tables, views, stored procedures, and other database objects.

• They can be used to reference objects in other databases or even on other servers.

• Synonyms ca...read more

I cannot disclose my personal email id for privacy reasons.

• I prefer to communicate through official channels provided by the company.

• Sharing personal email id can lead to security risks.

• I can provide an alternate email id for official communication.

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.

• Optimization techniques for joins include using indexes on join columns, avoiding unnecessary joins, and using appropriate join algorithms like nested loops or hash joins.

• Example: SELECT * FROM table1 INNER JOIN table2 ON table1.id = table2.id;

A unique key is a column or a set of columns in a database table that uniquely identifies each row.

• A unique key ensures that no two rows in a table have the same values for the specified column(s).

• It is used to enforce data integrity and prevent duplicate entries.

• A table can have multiple unique keys, but each unique key can only have one row with a specific set of values.

• Unique keys can be used as a reference for relationships between tables.

A view in SQL is a virtual table based on the result set of a SELECT query. There are different types of views like simple, complex, indexed, etc.

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

• Types of views include simple views, complex views, indexed views, etc.

• Views can be used to restrict access to certain columns or rows of a table.

• Views can improve performance by pre-computing expensive queries and storing the results.

Difference between delete vs drop vs truncate

• DELETE is used to remove specific rows from a table

• DROP is used to remove an entire table from the database

• TRUNCATE is used to remove all rows from a table

• DELETE can be rolled back, DROP and TRUNCATE cannot be rolled back

• DELETE is slower than TRUNCATE and DROP

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

Constraints are rules that are enforced on data columns in a table to ensure data integrity and accuracy.

• Constraints can be used to enforce uniqueness, primary keys, foreign keys, and check conditions on data.

• Examples include UNIQUE, PRIMARY KEY, FOREIGN KEY, and CHECK constraints.

• Constraints help maintain data integrity by preventing invalid data from being inserted into tables.

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 in a single query.

• There are different types of joins like inner join, left join, right join, and full outer join.

• Example: SELECT * FROM table1 INNER JOIN table2 ON table1.column = table2.column;

Query to find sales from the last quarter

• Use the SUM() function to calculate total sales

• Filter the data based on the date range of the last quarter

• Group by the relevant time period (e.g. month) to get a breakdown of sales

Compilation in SQL refers to the process of converting SQL code into an executable form, while recompilation occurs when changes are made.

• Compilation occurs when a SQL statement is first executed, creating an execution plan.

• Recompilation happens when the underlying data or schema changes, requiring a new execution plan.

• Example of recompilation: Changing a table structure (e.g., adding a column) may trigger recompilation of dependent stored procedures.

• SQL Server caches executi...read more

Indexes and keys are essential database structures that enhance data retrieval and enforce data integrity.

• Primary Key: Uniquely identifies each record in a table. Example: 'user_id' in a 'users' table.

• Foreign Key: Establishes a relationship between two tables. Example: 'user_id' in 'orders' table referencing 'users'.

• Unique Key: Ensures all values in a column are unique. Example: 'email' in a 'users' table.

• Composite Key: A combination of two or more columns to uniquely identif...read more

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';

Indexes are used to improve query performance. Clustered index determines physical order of data in a table.

• Indexes are used to quickly retrieve data from a table

• Clustered index determines the physical order of data in a table

• Clustered index is created on the primary key column by default

• Example: A clustered index on a customer ID column in a sales table would physically order the data by customer ID

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

• Indexes are used to quickly locate data without having to search every row in a table.

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

• Indexes can be clustered or non-clustered.

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

• Non-clustered indexes are separate structures that contain a copy of the indexed columns and a pointer to the actual data.

• Indexes can improve...read more

Synonyms are alternate names for database objects. They are used to simplify queries and provide security.

• Synonyms are used to provide an alternate name for a database object such as a table, view, stored procedure, or function.

• They can simplify queries by providing a shorter or more meaningful name for an object.

• Synonyms can also be used to provide security by allowing users to access an object without knowing its actual name or location.

• They are created using the CREATE SYN...read more

COALESCE is a function that returns the first non-null value in a list of expressions.

• COALESCE is used to simplify complex SQL statements.

• It can be used with any data type.

• It takes two or more arguments and returns the first non-null value.

• If all arguments are null, it returns null.

• Example: COALESCE(column1, column2, 'N/A') will return the value of column1 if it's not null, else column2 if it's not null, else 'N/A'.

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

• Normalization involves breaking down data into smaller, more manageable tables

• It helps in reducing data redundancy by storing data in a structured manner

• Normalization ensures data integrity by minimizing data anomalies

• There are different normal forms such as 1NF, 2NF, 3NF, BCNF, and 4NF

Different types of joins in SQL and their explanations

• 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 Outer Join - returns rows when there is a match in one of the tables

• Cross Join - returns the Cartesian product of the two tables

SQL join types allow combining data from multiple tables based on a specified condition.

• Inner Join: Returns rows that have matching values 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 Outer Join: Returns all rows when there is a match in either left or right table.

• Self Join: Joining a table with itself to combine rows base...read more

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

• There are different types of joins: inner join, left join, right join, and full outer join.

• 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 fro...read more

The syntax of a procedure in SQL is similar to that of a function, but it does not return a value.

• CREATE PROCEDURE procedure_name

• AS

• BEGIN

• -- SQL statements

• END;

SQL is a programming language used to manage and manipulate relational databases. Joins are used to combine data from multiple tables.

• SQL stands for Structured Query Language

• It is used to create, modify, and query databases

• 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

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