10+ SQL Server Developer Interview Questions and Answers

Different types of SQL joins with given data sets a and b.

• Inner join: Returns rows where there is a match in both tables (1,1)

• Left join: Returns all rows from the left table and the matched rows from the right table (1,1,1,2,2)

• Right join: Returns all rows from the right table and the matched rows from the left table (1,1,2,4)

• Cross join: Returns the Cartesian product of the two tables (1,1,1,1,1,2,1,4,1,1,2,1,2,2,1,4,2,1,2,2,2,2,4,3,1,1,3,1,2,3,1,4,3,1,1,3,2,2,3,2,4,3,1,2,3,2,...read more

Indexes are data structures that improve the speed of data retrieval operations in a database.

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

• Types of indexes include clustered, non-clustered, unique, and composite indexes.

• Clustered indexes determine the physical order of data in a table, while non-clustered indexes store a separate copy of the indexed columns.

• Unique indexes ensure that no two rows have the same values in the ind...read more

GROUP BY is used to group rows that have the same values into summary rows, while HAVING is used to filter groups based on a specified condition.

• GROUP BY is used with aggregate functions to group the result set by one or more columns.

• HAVING is used to filter groups based on a specified condition after the GROUP BY clause.

• GROUP BY is used before the HAVING clause in a query.

• Example: SELECT department, COUNT(*) FROM employees GROUP BY department HAVING COUNT(*) > 5;

Primary key uniquely identifies each record in a table, while Unique key allows only one instance of a value in a column.

• Primary key does not allow NULL values, while Unique key allows one NULL value.

• Primary key automatically creates a clustered index, while Unique key creates a non-clustered index by default.

• Primary key can be referenced by foreign keys, while Unique key cannot be referenced by foreign keys.

row_number, rank, dense_rank are window functions in SQL used to assign a unique number to each row based on specified criteria.

• row_number() assigns a unique sequential integer starting from 1 to each row in the result set

• rank() assigns a unique rank to each row based on the specified ordering criteria, with gaps in ranking for ties

• dense_rank() assigns a unique rank to each row based on the specified ordering criteria, with no gaps in ranking for ties

Integrity constraints are rules that ensure data integrity and consistency in a database.

• Integrity constraints are used to enforce business rules and maintain data accuracy.

• Common types of integrity constraints include primary key, foreign key, unique key, and check constraints.

• For example, a primary key constraint ensures that each row in a table is uniquely identified by a specific column or combination of columns.

DML commands are Data Manipulation Language commands used to manage data in a database.

• DML commands include INSERT, UPDATE, DELETE, and SELECT.

• INSERT is used to add new rows of data into a table.

• UPDATE is used to modify existing data in a table.

• DELETE is used to remove rows of data from a table.

• SELECT is used to retrieve data from a database.

Types of joins in SQL are Inner Join, Left Join, Right Join, and Full Join.

• Inner Join: Returns rows when there is a 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 Join: Returns rows when there is a match in one of the tables.

Execution plan is a roadmap that SQL Server uses to execute a query, showing the steps taken to retrieve data.

• Execution plan is generated by the query optimizer to determine the most efficient way to execute a query.

• It shows the order in which tables are accessed, joins are performed, and filters are applied.

• Execution plan can be viewed using tools like SQL Server Management Studio or by using the EXPLAIN statement in some databases.

A stored procedure is a precompiled collection of SQL statements that can be executed by calling the procedure name.

• Stored procedures can accept input parameters and return output parameters.

• They can be used to encapsulate complex logic and improve performance by reducing network traffic.

• Stored procedures are stored in the database and can be reused by multiple applications or users.

• Example: CREATE PROCEDURE GetEmployeeDetails AS SELECT * FROM Employees WHERE Department = 'IT...read more

A trigger is a special type of stored procedure that automatically executes when certain events occur in a database.

• Triggers can be used to enforce business rules, maintain referential integrity, and automate repetitive tasks.

• Examples of trigger events include INSERT, UPDATE, and DELETE operations on a table.

• Triggers can be defined to execute before or after the triggering event.

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.

• Types of joins include Inner Join, Left Join, Right Join, and Full Outer Join.

• Join conditions are specified using the ON keyword.

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

• Joins can also be nested to combine more than two tables.

Different types of joins in SQL include inner join, left join, right join, and full outer join.

• Inner join: Returns rows when there is a 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 either table.

The key of reusability in SQL Server development is creating modular, efficient code that can be easily adapted and reused.

• Use stored procedures and functions to encapsulate logic for reuse.

• Implement common table expressions (CTEs) to simplify complex queries that are used frequently.

• Utilize user-defined data types and user-defined functions to standardize data processing tasks.

• Leverage views to encapsulate complex queries and make them reusable across multiple queries or rep...read more