The Ultimate SQL Interview Guide for 2023: Download the Free PDF with Real-World Problems and Soluti

SQL Interview Questions and Answers for Experienced PDF Free Download

If you are looking for a job as a data analyst, data engineer, or database administrator, you need to have a solid knowledge of SQL. SQL, or Structured Query Language, is the standard language for manipulating and analyzing data stored in relational databases. SQL allows you to perform various tasks such as creating, updating, deleting, querying, and joining data from different tables.

One of the best ways to prepare for your SQL interview is to download a PDF of SQL interview questions and answers for experienced. This will help you to review the most common and important topics that are likely to be asked in your interview. You will also be able to practice your SQL skills by writing queries based on the given scenarios. By downloading a PDF of SQL interview questions and answers for experienced, you will be able to access it anytime and anywhere, even without an internet connection.

sql interview questions and answers for experienced pdf free download

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In this article, we will provide you with an overview of some of the key concepts and topics that you should know for your SQL interview. We will also provide you with a link to download the PDF of SQL interview questions and answers for experienced at the end of the article. Let's get started!

SQL Basics

Before we dive into the more advanced topics, let's review some of the basic concepts that you should know about SQL.

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What is a database and what are the types of databases?

A database is an organized collection of data that can be accessed and manipulated by software applications. There are two main types of databases: relational databases and non-relational databases.

Relational databases store data in tables, which consist of rows (records) and columns (fields). Each table has a unique name and a primary key that identifies each row. Tables can be related to each other by using foreign keys that reference the primary keys of other tables. Relational databases follow the ACID properties (Atomicity, Consistency, Isolation, Durability) that ensure data integrity and reliability. Some examples of relational database management systems (RDBMS) are MySQL, Oracle, SQL Server, PostgreSQL, etc.

Non-relational databases store data in different formats such as documents, key-value pairs, graphs, or columns. They do not follow a fixed schema or structure like relational databases. They are more flexible, scalable, and suitable for handling large volumes of unstructured or semi-structured data. They do not guarantee ACID properties but rather follow the BASE properties (Basically Available, Soft state, Eventual consistency) that allow for faster performance and availability. Some examples of non-relational database management systems (NoSQL) are MongoDB, Cassandra, Redis, Neo4j, etc.

What is a table and what are the components of a table?

A table is a collection of data that is organized in rows and columns. A table has a unique name and a primary key that identifies each row. A table can have one or more columns, each of which has a name and a data type. A column can also have constraints that define the rules and restrictions for the data stored in it. Some of the common constraints are NOT NULL, UNIQUE, CHECK, DEFAULT, and FOREIGN KEY.

Here is an example of a table that stores information about employees:

emp_id

emp_name

emp_dept

emp_salary

101

Alice

Marketing

5000

102

Bob

Sales

6000

103

Charlie

IT

7000

104

David

HR

8000

105

Eve

Finance

9000

In this table, emp_id is the primary key, emp_name and emp_dept are NOT NULL columns, and emp_salary is a DEFAULT column with a value of 4000.

What are the data types and constraints in SQL?

Data types define the kind of data that can be stored in a column. SQL supports various data types such as numeric, character, date and time, binary, etc. Some of the common data types are:

• INT: An integer value.

• FLOAT: A floating-point number with a decimal point.

• VARCHAR: A variable-length character string.

• CHAR: A fixed-length character string.

• DATE: A date value in the format YYYY-MM-DD.

• TIMESTAMP: A date and time value in the format YYYY-MM-DD HH:MM:SS.

• BLOB: A binary large object that can store images, videos, etc.

• CLOB: A character large object that can store text documents, etc.

The syntax for specifying the data type of a column is:

COLUMN_NAME DATA_TYPE (SIZE)

The size parameter is optional and defines the maximum length or precision of the data. For example, VARCHAR(20) means a variable-length character string with a maximum length of 20 characters.

Constraints define the rules and restrictions for the data stored in a column. They help to ensure data integrity and consistency. Some of the common constraints are:

• NOT NULL: This constraint ensures that a column cannot have a NULL value.

• UNIQUE: This constraint ensures that a column cannot have duplicate values.

• CHECK: This constraint ensures that a column satisfies a specified condition.

• DEFAULT: This constraint provides a default value for a column when no value is specified.

• FOREIGN KEY: This constraint references the primary key of another table to establish a relationship between two tables.

• PRIMARY KEY: This constraint uniquely identifies each row in a table. It is a combination of NOT NULL and UNIQUE constraints.

The syntax for specifying the constraints of a column is:

COLUMN_NAME DATA_TYPE (SIZE) CONSTRAINT_NAME CONSTRAINT_TYPE

The constraint_name parameter is optional and defines the name of the constraint. The constraint_type parameter defines the type of the constraint. For example, emp_id INT NOT NULL PRIMARY KEY means that emp_id is an integer column that cannot be NULL and is the primary key of the table.

SQL Queries

A SQL query is a statement that allows you to perform various operations on the data stored in a database. You can use SQL queries to create, update, delete, or retrieve data from one or more tables. The most common SQL command for querying data is SELECT, which has the following syntax:

SELECT column_list FROM table_list WHERE condition GROUP BY column_list HAVING condition ORDER BY column_list LIMIT number;

The SELECT clause specifies the columns to be retrieved from the tables. You can use the asterisk (*) to select all columns from the tables. You can also use aliases to rename the columns or tables for readability or convenience.

The FROM clause specifies the tables to be queried from the database. You can use commas to separate multiple tables if you want to query data from more than one table. You can also use aliases to rename the tables for readability or convenience.

The WHERE clause specifies the condition that filters the rows to be retrieved from the tables. You can use various operators such as =, , =, , !=, LIKE, IN, BETWEEN, etc. to define the condition. You can also use logical operators such as AND, OR, and NOT to combine multiple conditions.

The GROUP BY clause specifies the columns to group the rows based on some criteria. You can use this clause when you want to perform some aggregate functions such as SUM, AVG, COUNT, MIN, MAX, etc. on the grouped data.

The HAVING clause specifies the condition that filters the groups to be retrieved from the tables. You can use this clause when you want to apply some condition on the aggregated data.

The ORDER BY clause specifies the columns to sort the rows in ascending or descending order. You can use ASC or DESC keywords to specify the order. By default, the order is ascending.

The LIMIT clause specifies the number of rows to be retrieved from the tables. You can use this clause when you want to limit the result set to a certain number of rows.

Here is an example of a SQL query that uses all the clauses of the SELECT statement:

SELECT e.emp_name AS name, d.dept_name AS department, SUM(s.salary) AS total_salary FROM employee e JOIN department d ON e.dept_id = d.dept_id JOIN salary s ON e.emp_id = s.emp_id WHERE e.emp_name LIKE 'A%' GROUP BY e.emp_name, d.dept_name HAVING SUM(s.salary) > 10000 ORDER BY total_salary DESC LIMIT 5;

This query retrieves the name, department, and total salary of the employees whose name starts with 'A' and whose total salary is more than 10000. It joins three tables: employee, department, and salary using foreign keys. It groups the data by name and department and filters the groups by total salary. It sorts the data by total salary in descending order and limits the result set to 5 rows.

SQL Advanced Topics

Now that we have covered some of the basic topics of SQL, let's move on to some of the advanced topics that you should know for your SQL interview.

What are indexes and how to create and use them?

An index is a data structure that improves the speed of data retrieval from a table. An index creates a pointer to the rows in a table based on one or more columns that are used frequently in queries. An index can also enforce uniqueness on a column or a combination of columns.

An index can be created using the CREATE INDEX statement with the following syntax:

CREATE INDEX index_name ON table_name (column_list);

The index_name parameter specifies the name of the index. The table_name parameter specifies the name of the table on which the index is created. The column_list parameter specifies one or more columns that are included in the index.

An index can be used implicitly or explicitly in queries. An implicit use of an index means that the database engine decides whether to use an index or not based on various factors such as query complexity, table size, etc. An explicit use of an index means that you specify which index to use in your query using hints or keywords such as USE INDEX, FORCE INDEX, etc.

Here is an example of creating and using an index:

CREATE INDEX emp_name_index ON employee (emp_name); SELECT * FROM employee USE INDEX (emp_name_index) WHERE emp_name = 'Alice';

This example creates an index on emp_name column in employee table and uses it explicitly in a query that searches for employees with name 'Alice'. What are views and how to create and use them?

A view is a virtual table that is based on the result of a SQL query. A view does not store any data in the database, but rather displays the data from one or more tables as if it were a table. A view can be used to simplify complex queries, hide sensitive data, or provide a different perspective of the data.

A view can be created using the CREATE VIEW statement with the following syntax:

CREATE VIEW view_name AS SELECT column_list FROM table_list WHERE condition;

The view_name parameter specifies the name of the view. The SELECT statement defines the query that provides the data for the view. The column_list, table_list, and condition parameters are the same as in the SELECT statement.

A view can be used in queries like a regular table. You can use the SELECT, INSERT, UPDATE, or DELETE statements on a view, as long as the view is updatable. A view is updatable if it meets certain criteria, such as having a one-to-one relationship with the underlying table, not containing any aggregate functions, not containing any joins, etc.

Here is an example of creating and using a view:

CREATE VIEW emp_dept_view AS SELECT e.emp_id, e.emp_name, d.dept_name FROM employee e JOIN department d ON e.dept_id = d.dept_id; SELECT * FROM emp_dept_view WHERE dept_name = 'IT';

This example creates a view that shows the employee id, name, and department name from employee and department tables. It then uses the view to query the employees who belong to the IT department.

What are stored procedures and how to create and use them?

A stored procedure is a set of SQL statements that can be executed as a single unit. A stored procedure can perform various tasks such as validating input parameters, performing calculations, inserting, updating, or deleting data, returning results, etc. A stored procedure can improve the performance, security, and modularity of your SQL code.

A stored procedure can be created using the CREATE PROCEDURE statement with the following syntax:

CREATE PROCEDURE procedure_name (parameter_list) BEGIN SQL_statements; END;

The procedure_name parameter specifies the name of the stored procedure. The parameter_list parameter specifies one or more input or output parameters for the stored procedure. The SQL_statements parameter specifies one or more SQL statements that define the logic of the stored procedure.

A stored procedure can be executed using the CALL statement with the following syntax:

CALL procedure_name (argument_list);

The procedure_name parameter specifies the name of the stored procedure. The argument_list parameter specifies one or more values that match the parameters of the stored procedure.

Here is an example of creating and using a stored procedure:

CREATE PROCEDURE raise_salary (IN emp_id INT, IN percentage DECIMAL(5,2), OUT new_salary DECIMAL(10,2)) BEGIN SELECT salary INTO new_salary FROM employee WHERE employee.emp_id = emp_id; SET new_salary = new_salary * (1 + percentage / 100); UPDATE employee SET salary = new_salary WHERE employee.emp_id = emp_id; END; CALL raise_salary (101, 10, @new_salary); SELECT @new_salary;

This example creates a stored procedure that raises the salary of an employee by a given percentage and returns the new salary. It then calls the stored procedure with emp_id 101 and percentage 10 and displays the new salary.

Conclusion

In this article, we have covered some of the essential topics that you should know for your SQL interview. We have discussed SQL basics such as databases, tables, data types, and constraints. We have also discussed SQL queries such as SELECT, JOIN, GROUP BY, HAVING, ORDER BY, and LIMIT clauses. We have also discussed SQL advanced topics such as indexes, views, and stored procedures.

We hope that this article has helped you to refresh your SQL knowledge and prepare for your SQL interview. If you want to download a PDF of SQL interview questions and answers for experienced, you can click on this link: .

FAQs

Here are some frequently asked questions about SQL interview questions and answers for experienced:

Q: How do you write comments in SQL?

A: You can write comments in SQL using two ways:

Single-line comments: You can write single-line comments by using two hyphens (--). For example:

-- This is a single-line comment SELECT * FROM employee;

Multi-line comments: You can write multi-line comments by using /* and */. For example:

/* This is a multi-line comment */ SELECT * FROM employee;

Q: How do you handle NULL values in SQL?

A: NULL values represent missing or unknown data in SQL. You can handle NULL values in SQL using various ways:

IS NULL and IS NOT NULL operators: You can use these operators to check whether a column or an expression is NULL or not. For example:

SELECT * FROM employee WHERE emp_dept IS NULL;

This query returns the employees who do not have a department assigned.

COALESCE function: You can use this function to return the first non-NULL value from a list of values. For example:

SELECT COALESCE(emp_name, 'Unknown') AS name FROM employee;

This query returns the employee name or 'Unknown' if the name is NULL.

NULLIF function: You can use this function to return NULL if two values are equal, otherwise return the first value. For example:

SELECT NULLIF(emp_salary, 0) AS salary FROM employee;

This query returns the employee salary or NULL if the salary is zero.

Q: How do you optimize SQL queries for performance?

A: You can optimize SQL queries for performance using various techniques such as:

• Using indexes: You can create indexes on columns that are frequently used in queries, especially in the WHERE, JOIN, GROUP BY, and ORDER BY clauses. Indexes can speed up data retrieval by reducing the number of disk accesses.

• Using joins: You can use joins to combine data from multiple tables instead of using subqueries or nested queries. Joins can improve performance by reducing the number of queries and the amount of data transferred.

• Using filters: You can use filters to limit the number of rows returned by a query. You can use the WHERE clause to filter data based on some condition, and the LIMIT clause to limit the number of rows returned. Filters can improve performance by reducing the amount of data processed and transferred.

• Using aggregations: You can use aggregations to perform calculations on data such as SUM, AVG, COUNT, MIN, MAX, etc. You can use the GROUP BY clause to group data based on some criteria, and the HAVING clause to filter groups based on some condition. Aggregations can improve performance by reducing the amount of data processed and transferred.

• Using functions: You can use functions to perform some operations on data such as CONCAT, SUBSTR, UPPER, LOWER, etc. Functions can improve performance by reducing the amount of code and complexity.

Q: How do you handle errors and exceptions in SQL?

A: Errors and exceptions are unexpected or undesirable situations that occur during the execution of SQL statements. You can handle errors and exceptions in SQL using various ways such as:

Using TRY...CATCH blocks: You can use these blocks to execute a set of statements and catch any errors or exceptions that occur. You can use the ERROR_NUMBER, ERROR_MESSAGE, ERROR_SEVERITY, ERROR_STATE, etc. functions to get information about the error or exception. You can also use the RAISERROR or THROW statements to generate custom errors or exceptions. For example:

BEGIN TRY -- Try block SELECT 1 / 0; -- This will cause a divide by zero error END TRY BEGIN CATCH -- Catch block SELECT ERROR_NUMBER() AS ErrorNumber, ERROR_MESSAGE() AS ErrorMessage; END CATCH;

This example tries to execute a statement that causes a divide by zero error and catches it in the catch block. It then displays the error number and message.

Using transactions: You can use transactions to group a set of statements that should be executed as a single unit. You can use the BEGIN TRANSACTION, COMMIT TRANSACTION, and ROLLBACK TRANSACTION statements to start, end, and undo a transaction. Transactions follow the ACID properties that ensure data integrity and reliability. For example:

BEGIN TRANSACTION -- Transaction block UPDATE employee SET salary = salary * 1.1 WHERE emp_id = 101; UPDATE department SET budget = budget - 1000 WHERE dept_id = 1; COMMIT TRANSACTION;

This example executes a transaction that updates the salary of an employee and the budget of a department. It commits the transaction if there are no errors or exceptions, otherwise it rolls back the transaction to the previous state.

Q: How do you test and debug SQL queries?

A: Testing and debugging SQL queries are important steps to ensure the correctness and quality of your SQL code. You can test and debug SQL queries using various tools and techniques such as:

• Using a SQL editor or IDE: You can use a SQL editor or IDE (Integrated Development Environment) that provides features such as syntax highlighting, code completion, error checking, formatting, etc. to write and execute your SQL queries. Some examples of SQL editors or IDEs are SQL Server Management Studio, MySQL Workbench, Oracle SQL Developer, etc.

• Using a testing framework: You can use a testing framework that allows you to write and run automated tests for your SQL queries. You can use assertions to verify the expected results and outcomes of your queries. You can also use mock data to simulate different scenarios and cases for your queries. Some examples of testing frameworks are tSQLt, SQLUnit, dbUnit, etc.

• Using a debugger: You can use a debugger that allows you to step through your SQL queries and examine the values of variables, parameters, expressions, etc. You can also set breakpoints, watchpoints, and tracepoints to pause and resume the execution of your queries. You can also use logging and printing statements to display the output or status of your queries. Some examples of debuggers are SQL Debugger, PL/SQL Debugger, MySQL Debugger, etc.

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