Tsql Interview Questions For Experienced Professionals
T-SQL Interview Questions for Seasoned Professionals
Tsql Interview Questions For Experienced Professionals
During TSQL interviews for experienced professionals, candidates can expect questions that delve into their deep understanding and practical application of TSQL concepts. Interviewers may inquire about complex joins, subqueries, optimization techniques, indexing strategies, performance tuning, handling of large datasets, error handling, and best practices for writing efficient TSQL code. Candidates should also be prepared to discuss their experience with stored procedures, user-defined functions, triggers, views, and transaction management. Additionally, they may be asked to solve real-world scenarios and demonstrate their problem-solving abilities using TSQL. It's essential for experienced professionals to showcase their expertise in writing optimized, scalable, and maintainable TSQL code to excel in such interviews.
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1 - Describe the differences between Clustered and Non Clustered Indexes in SQL Server.
Clustered indexes determine the physical order of the table data, as the rows are sorted and stored in the order of the clustered index key. Each table can only have one clustered index. Non clustered indexes, on the other hand, do not affect the physical order of the table data and are stored separately, with each node pointing to the actual row in the table. A table can have multiple non clustered indexes.
2) Explain the purpose of the ROW_NUMBER() function in T SQL.
The ROW_NUMBER() function in T SQL assigns a unique incremental value to each row within a result set. It is often used in conjunction with the ORDER BY clause to generate a row number for each row based on a specified criteria, allowing users to rank or filter data in a specific order.
3) How does the MERGE statement work in SQL Server?
The MERGE statement in SQL Server combines INSERT, UPDATE, and DELETE operations into a single statement, allowing users to synchronize data between two tables based on a specified condition. It first matches the source and target tables based on the defined criteria and performs the appropriate action (INSERT, UPDATE, DELETE) for each matched or unmatched row.
4) What are Common Table Expressions (CTEs) and when would you use them?
Common Table Expressions (CTEs) are temporary result sets that can be referenced within a SELECT, INSERT, UPDATE, or DELETE statement. They improve the readability and maintainability of complex queries by breaking them down into smaller, more manageable parts. CTEs are particularly useful when a query requires multiple references to the same subquery or when recursive queries are needed.
5) Discuss the differences between TRUNCATE TABLE and DELETE statements in SQL.
TRUNCATE TABLE is a DDL (Data Definition Language) statement that removes all rows from a table in a more efficient manner than the DELETE statement, as it does not log individual row deletions. However, TRUNCATE TABLE cannot be rolled back and does not trigger any associated triggers. DELETE, on the other hand, is a DML (Data Manipulation Language) statement that removes specific rows based on a condition and can be rolled back if required. It is slower than TRUNCATE TABLE but provides more flexibility and control over which rows to delete.
6) What is the purpose of the PIVOT and UNPIVOT operators in T SQL?
The PIVOT operator in T SQL allows users to rotate rows into columns, aggregating data and providing a more condensed view of information. UNPIVOT, on the other hand, reverts aggregated column wise data back into rows. These operators are commonly used in reporting and data analysis scenarios where data transformation is required for better visualization and analysis purposes.
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