HCLTech SQL Developer Interview Questions and Answers

Q1. Difference between keys and indexes in sql
Ans. 
Keys uniquely identify records, while indexes improve query performance by speeding up data retrieval.
• A primary key is a unique identifier for a record in a table, e.g., 'user_id' in a 'users' table.

• A foreign key establishes a relationship between two tables, e.g., 'order_id' in 'orders' referencing 'user_id' in 'users'.

• Indexes are data structures that improve the speed of data retrieval operations on a database table,...read more
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Q2. Is keys creates a index ?
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Keys in SQL create indexes to enhance data retrieval speed and enforce uniqueness in tables.
• Primary Key: Automatically creates a unique index on the column(s) defined as the primary key, ensuring no duplicate values. Example: `PRIMARY KEY (id)`.

• Foreign Key: May create an index to improve join performance between tables. Example: `FOREIGN KEY (user_id) REFERENCES users(id)`.

• Unique Key: Creates a unique index to enforce ...read more
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Q3. What r the types of index and keys?
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Indexes and keys are essential database structures that enhance data retrieval and enforce data integrity.
• Primary Key: Uniquely identifies each record in a table. Example: 'user_id' in a 'users' table.

• Foreign Key: Establishes a relationship between two tables. Example: 'user_id' in 'orders' table referencing 'users'.

• Unique Key: Ensures all values in a column are unique. Example: 'email' in a 'users' table.

• Composite Key...read more
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Q4. Difference between identity and sequenceNo with more details?
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Identity columns auto-generate values for new rows, while sequences are independent objects for generating unique numbers.
• Identity: Automatically generates a unique value for each new row in a table.

• Example: In SQL Server, you can define a column as 'IDENTITY(1,1)' to start at 1 and increment by 1.

• Sequence: A separate database object that generates a sequence of numeric values.

• Example: In Oracle, you can create a seque...read more
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Q5. Difference between truncate and drop with more details. eg: 'A' table have a identity column with 10 rows. if I tried to delete or truncate a 2nd row, then what will be next value of identity column? (Plea...read more
Ans. 
Truncate removes all rows and resets identity, while delete removes specific rows without resetting identity.
• TRUNCATE TABLE removes all rows from a table and resets any identity columns to their seed value.

• DELETE FROM table_name removes specific rows based on a condition but does not reset identity columns.

• Example: If 'A' table has 10 rows with an identity column starting at 1, truncating will reset the next identity v...read more
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Q6. What is compile and recompile in sql?
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Compilation in SQL refers to the process of converting SQL code into an executable form, while recompilation occurs when changes are made.
• Compilation occurs when a SQL statement is first executed, creating an execution plan.

• Recompilation happens when the underlying data or schema changes, requiring a new execution plan.

• Example of recompilation: Changing a table structure (e.g., adding a column) may trigger recompilatio...read more
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Q7. What is execution plan?
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An execution plan is a roadmap that outlines how a SQL query will be executed by the database engine.
• It shows the steps the database will take to execute a query, including joins, scans, and sorts.

• Execution plans can be visualized using tools like SQL Server Management Studio or EXPLAIN in PostgreSQL.

• They help identify performance bottlenecks by showing which operations are most costly.

• Example: A query that joins two t...read more
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Q8. Uses of storeprocedures? (Eg: Execution plan use)
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Stored procedures are precompiled SQL statements that enhance performance, security, and maintainability in database operations.
• Performance Optimization: Stored procedures are precompiled, which means the execution plan is cached, reducing the overhead of query parsing and optimization.

• Code Reusability: They allow developers to encapsulate complex logic in a single procedure, which can be reused across multiple applica...read more
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Q9. Sql server architecture basic?
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SQL Server architecture consists of a database engine, storage engine, and various services for data management and processing.
• 1. SQL Server Database Engine: Core component responsible for data storage, processing, and security.

• 2. Storage Engine: Manages how data is stored on disk, including data files and transaction logs.

• 3. SQL Server Services: Includes services like SQL Server Agent for job scheduling and SQL Server...read more
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Q10. Can we crud operation inside a function or view?
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CRUD operations are not allowed inside functions or views in SQL due to side effects and consistency issues.
• Functions in SQL are meant to return values and cannot perform data modification (INSERT, UPDATE, DELETE).

• Views are virtual tables and are used to present data; they do not support direct data manipulation.

• Using a function to perform CRUD can lead to unpredictable results and violate the principle of function pur...read more
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Q11. Can we call a procedure from a function?
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A function cannot directly call a procedure in SQL due to restrictions on side effects and transaction control.
• Functions are designed to return a value and cannot perform actions that modify database state, such as calling procedures.

• Procedures can be called from other procedures or anonymous blocks, but not from functions due to their side effects.

• Example: If you have a procedure that updates a table, calling it from ...read more
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Q12. Difference between table variable and temp table with example?
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Table variables and temp tables differ in scope, performance, and usage in SQL Server.
• Scope: Table variables are scoped to the batch, while temp tables are scoped to the session.

• Performance: Table variables are generally faster for small datasets, while temp tables can handle larger datasets better.

• Transaction Logging: Table variables have minimal logging, while temp tables are fully logged.

• Example of Table Variable: D...read more
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Q13. Query writing with joins and group by with having clause , where clause?
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Understanding SQL joins, group by, having, and where clauses for effective data querying.
• Joins combine rows from two or more tables based on a related column. Example: SELECT * FROM table1 JOIN table2 ON table1.id = table2.id;

• GROUP BY aggregates data across specified columns. Example: SELECT department, COUNT(*) FROM employees GROUP BY department;

• HAVING filters groups created by GROUP BY. Example: SELECT department, CO...read more
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Q14. Difference between where clause and having clause
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The WHERE clause filters rows before aggregation, while HAVING filters after aggregation in SQL queries.
• WHERE clause is used to filter records before any groupings are made.

• HAVING clause is used to filter records after aggregation functions like COUNT, SUM, AVG.

• Example of WHERE: SELECT * FROM employees WHERE salary > 50000;

• Example of HAVING: SELECT department, COUNT(*) FROM employees GROUP BY department HAVING COUNT...read more
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Q15. Type of functions and detailed explanation
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SQL functions are categorized into scalar, aggregate, and window functions, each serving distinct purposes in data manipulation.
• Scalar Functions: Operate on a single value and return a single value. Example: UPPER('abc') returns 'ABC'.

• Aggregate Functions: Operate on a set of values and return a single summary value. Example: COUNT(*) counts the number of rows.

• Window Functions: Perform calculations across a set of table...read more
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Q16. What is cursors? Create a cursor ( just to check whether u know write a cursor query) Alternate way to create a cursor(Answer is while loop)
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Cursors are database objects used to retrieve, manipulate, and navigate through a result set row by row.
• Cursors allow for row-by-row processing of SQL results.

• Types of cursors: implicit and explicit.

• Example of creating an explicit cursor: DECLARE cursor_name CURSOR FOR SELECT column_name FROM table_name;

• To fetch data from a cursor: FETCH cursor_name INTO variable_name;

• An alternate way to process rows is using a WHILE...read more
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Q1. Tell me about your self
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I am an experienced SQL Developer with a strong background in database management and query optimization.
• Experienced SQL Developer

• Strong background in database management

• Expertise in query optimization
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Q2. Why choose this company
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This company offers a collaborative work environment, cutting-edge technology, and opportunities for professional growth.
• Collaborative work environment: The company values teamwork and encourages collaboration among employees.

• Cutting-edge technology: The company stays up-to-date with the latest advancements in SQL development.

• Opportunities for professional growth: The company provides training programs and career devel...read more
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Basic concepts of aptitude and reasoning

Q1. They mostly ask from your resume
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Q2. Sql Quires on Joins, Stored procedures.
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Q1. Basic questions like your additional achievements if any, salary expectations.
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