You must master the SQL interview questions for experienced professionals to crack the most challenging interview rounds. Your in-depth knowledge of SQL is vital for dealing with large amounts of data, retrieving specific results, or drawing quick insights.
If you are applying for data scientists or data engineer positions at FAANG+ companies, you must go through the most anticipated SQL interview questions for experienced professionals. You must also practice SQL query interview questions for experienced professionals. Continue reading to assess your SQL tech interview prep and clear some of the crucial concepts.
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Here's what we'll cover:
- SQL Interview Questions for Experienced Professionals
- SQL Query Interview Questions for Experienced Professionals
- Oracle PL/SQL Interview Questions for Experienced Professionals
- Oracle SQL Interview Questions for Experienced Professionals
- FAQs on SQL Interview Questions
SQL Interview Questions for Experienced Professionals
You must go through the following curated list of SQL interview questions for experienced professionals, which are likely to be asked during the SQL interview.
Q1. What is normalization? What are the different normalizations?
The process of organizing fields and tables of a database to minimize redundancy and dependency. It allows you to add, delete or modify fields that can be incorporated into a single table. The different normalizations are
- First Normal Form (1NF): This should remove a table's duplicate columns. It is for the identification of unique columns and the creation of tables for the related data.
- Second Normal Form (2NF): A table is in its second normal form if it meets all requirements of the first normal form and places the subsets of data in separate tables. The relationships between tables are created using primary keys.
- Third Normal Form (3NF): The table should be in the second normal form. There should be no dependency on primary key constraints.
- Fourth Normal Form (4NF): It should meet all the requirements of the third normal form and should not have multi-valued dependencies.
Q2. What is denormalization?
Using the denormalization technique, you can access the data from higher to lower normal forms of the database. As the name suggests, it is a reversal of normalization, i.e., it introduces redundancy into a table as it incorporates data from the related tables.
Q3. What is collation? What are the different types of collation sensitivity?
It is a set of rules determining how character data can be sorted and compared. You can use collation to compare A and other language characters. It depends on the width of the characters. You can use ASCII values to compare these character data.
The different types of collation sensitivity are as follows:
- Case sensitivity such as A and a and B and b.
- Accent sensitivity
- Kana sensitivity for Japanese Kana characters.
- Width sensitivity such as for single-byte characters and double-byte characters.
Q4. What do you understand about CASE statements?
You can use a CASE statement to check certain conditions and return a value based on whether the conditions are evaluated as true. CASE allows you to bring logic, conditions, and order in combination with clauses like WHERE and ORDER BY.
A CASE expression is different from a CASE statement. An expression evaluates a list of conditions. It returns one of the multiple possible result expressions. Its result is a single value, whereas a CASE statement result is the execution of a sequence of statements.
Q5. What are some common SQL commands?
Some common commands are as follows:
- UNION: It combines the results of two tables. It also removes duplicate rows from the tables.
- MINUS: It returns rows from the first query and not from the second query.
- INTERSECT: It returns rows returned by both the queries.
- DELETE: It removes one or more rows from a table.
- TRUNCATE: It deletes all the rows from the table. Thus, it frees the space containing the table.
- INSERT: It inserts data into the row of a table.
- UPDATE: It updates or modifies the value of a column in the table.
- ALIAS: It is a name that you can give to a table or column. You can refer to this name in a WHERE clause to identify the table or column.
- ALTER: It alters the structure of the database. It allows you to add a column or modify an existing one.
- DROP: It removes tables and databases from RDBMS.
- CREATE: It defines the database structure schema.
- GRANT: It gives the user access privileges to a database.
- REVOKE: It takes back permissions from the user.
- COMMIT: It saves all the transactions to the database.
- ROLLBACK: It allows you to undo transactions that haven't been saved to the database.
- SAVEPOINT: It allows you to set a savepoint within a transaction.
- SELECT: It selects the attribute as described by the WHERE clause.
SQL Query Interview Questions for Experienced Professionals
The interviewers might present a SQL query and ask questions on the same. They can also ask you to write SQL queries. Here are some SQL query interview questions for experienced professionals.
- Write an SQL query to display the current date.
- Write an SQL query to verify if the data passed to the query is of the given format: "DD/MM/YY."
- Write an SQL query to print the candidate's name, whose birth date is 08/09/1970 to 30/11/1975.
- Write a query to print an employee's name whose name starts with 'S.'
- Write a query to find an employee whose salary is less than or equal to 10000.
- Write a query to find the month from a given date.
- Write a query to join three tables containing two NULL values.
- Write a query to fetch the first three characters of the employee name.
- Consider the following data table for answering the question given below:
Las Vegas (LAS)
San Diego (SAN)
Answer the following SQL query interview questions with reference to the above table:
- Write a SQL query to fetch the EmpFname in the upper case. Use the ALIAS name as EmpName.
- Write a SQL query to retrieve the number of employees who are a part of the HR department.
- Write a query to fetch the first four characters of EmpLname whose name starts with 'W.'
- Write a SQL query to retrieve the place name, i.e., the string before brackets, from the Address column.
- Write a SQL query to fetch the names of employees that begin with 'R.'
Recommended Reading: SQL query interview questions based on a sample data table
Oracle PL/SQL Interview Questions for Experienced Professionals
Oracle created PL/SQL to overcome the disadvantages of SQL. It allows easier building and handling of critical applications. The following Oracle PL/ SQL interview questions for experienced professionals will help you brush up on the concepts:
- What makes PL/SQL a better option than SQL?
- How would you debug your code in PL/SQL?
- How is the mutating table different from the constraining table?
- Where are the outcomes of the execution of the DML statement saved?
- What virtual tables are available during the execution of the database trigger?
- What is the significance of the SYS.ALL_DEPENDENCIES?
- What is the difference between %TYPE and %ROWTYPE data types in PL/SQL?
- Write a PL/SQL program to calculate the sum of the digits of a three-digit number?
- What are the different ways of commenting in a PL/SQL code?
- What is exception handling?
- What do you understand about INSTEAD OF triggers?
- What do you understand about PL/SQL records?
Oracle SQL Interview Questions for Experienced Professionals
Here is a list of the most commonly asked Oracle SQL interview questions for experienced professionals.
- What is the NVL function? How would you use it?
- What is the use of the COALESCE function?
- What are Invalid_number and Value_error?
- What do you understand from the flashback query?
- What are trigger predicate clauses?
- What command allows the quickest fetching of the data from a table?
- How is a nested table different from a normal table?
You must practice these SQL interview questions for experienced professionals, and if you want more, you can go through 50+ SQL interview questions and tips on how to crack them.
FAQs on SQL Interview Questions for Experienced Professionals
Q1. Are SQL interview questions for experienced professionals important for data analysts?
If you are a data analyst, you need to have SQL knowledge to completely understand data available in Relational Databases such as MySQL, Oracle, and Microsoft SQL. You must get well-versed with SQL interview questions for experienced professionals related to Data Preparation and Wrangling. Also, if your job requires you to use Big Data Tools for analysis, then SQL interview questions are a must for your interview preparation.
Q2. What topics are important for SQL interview questions for experienced professionals?
If you aim to perform well at an SQL job interview, you must have complete knowledge of the vital concerts related to SQL, including Data Definition Language (DDL) keywords, Data Manipulation Language (DML) keywords, Data Control Language (DCL) keywords, Transaction Control Language (TCL) keywords, SQL constraints, joins, indexes, and transactions.
Q3. Is coding in SQL interview questions for experienced professionals hard?
If you are an experienced professional, you will not find coding questions in SQL hard. They are relatively easy as compared to other languages. With that said, you must practice as many coding problems as possible to ace the interview rounds.
Q4. How long does it take to learn SQL before an interview?
You can expect to become familiar with SQL basics within two to three weeks as SQL is a relatively simple language. If you are planning to apply for senior positions requiring SQL skills at work, you will need a higher level of fluency, which will take more than a month.
Q5. Which top companies make use of SQL?
With proficiency in SQL, you can land lucrative offers at some of the major organizations that make use of SQL, including Microsoft, NTT Data, Adobe, LinkedIn, Facebook, Cognizant, Dell, Accenture, and Stack Overflow.
Gear Up for Your Next Tech Interview
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