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We recommend using the following advanced SQL interview questions when you need to fill senior SQL positions. Candidates should already have a few years of experience in SQL. 35. What are SQL injections and how can they be avoided? Example answer : A SQL injection is a type of cyber attack that hackers use to insert malicious SQL code into the database to gain access to potentially valuable or sensitive information. It is very common in applications or websites that use SQL databases. To prevent this, you can create multiple database accounts to limit access, or use a third-party web application firewall. 36. How can SQL queries be optimized? Exa(select all) Combine elements with INNER JOIN instead of WHERE Define filters with WHERE instead of HAVING Avoid statement loops in the query structure Avoid correlated subqueries 37. What are the different types of normalization? Example answer : In SQL, the normalization process can be divided into six steps or types: First Normal Form (1NF): serves to ensure that rows and columns always contain unique, non-repeating values. Second normal form (2NF): used to eliminate partial dependencies.
Third normal form (3NF): serves to eliminate transitive functional dependencies. Boyce-Codd normal form (BNF) or fourth normal form (4FN): serves to ensure that all functional dependencies are a superkey of the Bahamas Mobile Number List table. Fifth Normal Form (5NF): This is to ensure that decomposition does not result in data loss. Sixth normal form (6NF): serves to decompose the relationship variables into irreducible components. 38. What are ACID properties in SQL? Example answer : ACID is the acronym for atomicity, coherence, isolation and durability. These properties are essential to ensure data integrity during a transaction. Function of each property: Atomicity: Changes to data are made in a single unified operation. Consistency: Data values are consistent at the beginning and end of the transaction. Isolation: A transaction cannot see the intermediate state of another transaction. Durability: Changes to data survive the transaction. 39. What are the different types of stored procedures? Example answer : Stored procedures are portions of SQL code that can be stored and reused.
These are the most important types of stored procedures: User-defined stored procedures: Procedures that users create. System Stored Procedures: Default procedures that are permanently saved in the system. Temporarily stored procedures: Procedures that are lost when the session is closed. Remotely Stored Procedures: Procedures that are created and saved on remote servers. 40. What query would you use to find staff who earn the same salary in a staffing table? Example answer : To find staff with the same salary, you can use the following solution: Use the SELECT statement to specify the relevant table. Use the FROM statement to specify the personnel column. Use the WHERE statement to specify the salary criteria. For example: WHERE salario IN (SELECT salary FROM employee WHERE employee.employee_id <> employee.employee_id ) 41. How do you remove duplicate rows in a table? Example answer : There are several ways to remove duplicate rows in a table. For example, you can do the following: Use common table expressions (CTEs) with the ROW_NUMBER function to identify and remove duplicate rows.
Third normal form (3NF): serves to eliminate transitive functional dependencies. Boyce-Codd normal form (BNF) or fourth normal form (4FN): serves to ensure that all functional dependencies are a superkey of the Bahamas Mobile Number List table. Fifth Normal Form (5NF): This is to ensure that decomposition does not result in data loss. Sixth normal form (6NF): serves to decompose the relationship variables into irreducible components. 38. What are ACID properties in SQL? Example answer : ACID is the acronym for atomicity, coherence, isolation and durability. These properties are essential to ensure data integrity during a transaction. Function of each property: Atomicity: Changes to data are made in a single unified operation. Consistency: Data values are consistent at the beginning and end of the transaction. Isolation: A transaction cannot see the intermediate state of another transaction. Durability: Changes to data survive the transaction. 39. What are the different types of stored procedures? Example answer : Stored procedures are portions of SQL code that can be stored and reused.
These are the most important types of stored procedures: User-defined stored procedures: Procedures that users create. System Stored Procedures: Default procedures that are permanently saved in the system. Temporarily stored procedures: Procedures that are lost when the session is closed. Remotely Stored Procedures: Procedures that are created and saved on remote servers. 40. What query would you use to find staff who earn the same salary in a staffing table? Example answer : To find staff with the same salary, you can use the following solution: Use the SELECT statement to specify the relevant table. Use the FROM statement to specify the personnel column. Use the WHERE statement to specify the salary criteria. For example: WHERE salario IN (SELECT salary FROM employee WHERE employee.employee_id <> employee.employee_id ) 41. How do you remove duplicate rows in a table? Example answer : There are several ways to remove duplicate rows in a table. For example, you can do the following: Use common table expressions (CTEs) with the ROW_NUMBER function to identify and remove duplicate rows.