20+ Senior Database Developer Interview Questions and Answers

Merge combines two result sets into one, while Union All combines and includes duplicates.

• Merge is used to combine two result sets into one, eliminating duplicates.

• Union All is used to combine two result sets into one, including duplicates.

• Merge requires the result sets to have the same number of columns and compatible data types.

• Union All does not require the result sets to have the same number of columns or data types.

SQL Server offers various numeric data types for storing different types of numerical values.

• SQL Server provides data types like int, bigint, smallint, tinyint for storing whole numbers.

• Numeric data types like decimal and numeric are used for storing fixed-point numbers.

• Float and real data types are used for storing floating-point numbers with different precision levels.

• Money and smallmoney data types are used for storing monetary values.

Snowflake schema has normalized dimension tables while Star schema has denormalized dimension tables.

• Snowflake schema has a centralized fact table connected to multiple dimension tables normalized into sub-dimension tables.

• Star schema has a denormalized structure with dimension tables directly connected to the fact table.

• Snowflake schema requires more joins for querying data compared to Star schema.

• Star schema is easier to understand and query but may lead to data redundancy....read more

Snow Flake Schema has better performance than Star Flake Schema.

• Snow Flake Schema has normalized tables which reduces data redundancy and improves query performance.

• Star Flake Schema has denormalized tables which can lead to data redundancy and slower query performance.

• Snow Flake Schema is better suited for complex queries with multiple joins.

• Star Flake Schema is better suited for simple queries with fewer joins.

• Performance also depends on the specific use case and data volum...read more

Normalization is the process of organizing data in a database to reduce redundancy and improve data integrity.

• Normalization involves breaking down data into smaller, more manageable tables

• It helps in reducing data redundancy by storing data in a structured manner

• Normalization ensures data integrity by minimizing anomalies such as update, insert, and delete anomalies

• There are different normal forms like 1NF, 2NF, 3NF, and BCNF that define the level of normalization

Different row transformations in SSIS include Conditional Split, Derived Column, Lookup, and Merge.

• Conditional Split: Routes data rows to different outputs based on specified conditions.

• Derived Column: Adds new columns or modifies existing columns using expressions.

• Lookup: Retrieves data from a related table based on a specified key.

• Merge: Combines data from multiple sources into a single dataset.

Explanation of database terms: Bookmarking, Row id, Key Index, covering index.

• Bookmarking is a feature that allows users to save the location of a record in a database for future reference.

• Row id is a unique identifier assigned to each row in a table.

• Key Index is an index created on a column or set of columns that uniquely identifies each row in a table.

• Covering index is an index that contains all the columns required to satisfy a query, so the database engine does not need t...read more

Isolation levels determine the level of visibility of changes made by other transactions.

• Isolation levels include Read Uncommitted, Read Committed, Repeatable Read, and Serializable.

• The default isolation level in most databases is Read Committed.

• To specify a different isolation level, you can use SQL statements like SET TRANSACTION ISOLATION LEVEL in SQL Server or SET TRANSACTION in Oracle.

Using sp_ prefix for stored procedures can cause performance issues and conflicts with system procedures.

• sp_ prefix is reserved for system stored procedures in SQL Server, so using it for user-defined procedures can lead to conflicts.

• Using sp_ prefix can cause unnecessary overhead as SQL Server first searches in the master database for system procedures before looking in the user database.

• Avoiding sp_ prefix can improve performance and prevent confusion with system procedures...read more

Event handlers in SSIS are workflows that are triggered by specific events during the execution of a package.

• Event handlers can be used to perform additional tasks or actions based on the success or failure of specific tasks within a package.

• Common events that can trigger event handlers include OnError, OnPreExecute, OnPostExecute, OnWarning, etc.

• Event handlers can be configured to send emails, log information, execute scripts, or perform other actions based on the event that...read more

Temp variables, tables, and CTE are used in SQL to store temporary data during query execution.

• Temp variables are used to store temporary data within a query.

• Temp tables are used to store temporary data that can be accessed by multiple queries.

• CTE (Common Table Expression) is a temporary result set that can be referenced within a SELECT, INSERT, UPDATE, or DELETE statement.

• Temp variables and tables are created using the # symbol before the variable or table name.

• CTE is create...read more

Event and error handling are crucial in SSIS to ensure smooth execution and proper handling of exceptions.

• Event handling involves capturing and responding to events that occur during package execution.

• Error handling involves identifying and handling errors that occur during package execution.

• SSIS provides various built-in event handlers and error handlers, such as OnError, OnTaskFailed, OnPostExecute, etc.

• Custom event handlers and error handlers can also be created using scri...read more

Types of triggers include DML triggers, DDL triggers, and logon triggers.

• DML triggers are fired in response to data manipulation language (DML) events like INSERT, UPDATE, DELETE.

• DDL triggers are fired in response to data definition language (DDL) events like CREATE, ALTER, DROP.

• Logon triggers are fired in response to a LOGON event.

• INSTEAD OF triggers are used to perform an action instead of the triggering action.

Merge combines two tables based on a specified condition, while union combines two tables with the same structure.

• Merge is used to update or insert data into a target table based on a join condition with a source table.

• Union is used to combine the results of two SELECT statements into a single result set.

• Merge requires a join condition and can perform insert, update, and delete operations.

• Union requires that both tables have the same number of columns and compatible data type...read more

Views can improve query performance by simplifying complex queries and reducing the need for redundant code.

• Views can store complex queries and calculations, allowing for easier access and reuse of data.

• Views can help optimize performance by pre-aggregating data or joining tables in advance.

• Views can reduce the need for writing repetitive code by encapsulating common logic.

• However, views can also introduce overhead if not properly indexed or if they involve complex calculatio...read more

Data types are classifications of data items that determine the nature of operations that can be performed on them.

• Numeric data types: int, float, double, decimal

• Character and string data types: char, varchar, text

• Date and time data types: date, time, datetime

• Boolean data type: bool

• Binary data types: binary, varbinary, image

Normalization is the process of organizing data in a database to reduce redundancy and dependency.

• It involves breaking down a table into smaller tables and defining relationships between them.

• Normalization helps to eliminate data inconsistencies and anomalies.

• There are different levels of normalization, with each level having specific rules to follow.

• For example, first normal form (1NF) requires that each column in a table be atomic, meaning it cannot be further divided into ...read more

CTE stands for Common Table Expression. It is used to create a temporary result set that can be referenced within a SELECT, INSERT, UPDATE, or DELETE statement.

• CTE is defined using the WITH keyword followed by a name and a SELECT statement.

• It can be used to simplify complex queries by breaking them down into smaller, more manageable parts.

• CTE can also improve query performance by reducing the number of times a table needs to be scanned.

• Example: WITH cte AS (SELECT * FROM myTa...read more

Transformations in SSIS are used to modify data during ETL process.

• Data Conversion Transformation

• Conditional Split Transformation

• Aggregate Transformation

• Sort Transformation

• Merge Transformation

• Lookup Transformation

• Derived Column Transformation

• Multicast Transformation

• Union All Transformation

• Pivot Transformation

• Unpivot Transformation

Yes, views can be updated in SQL.

• Views can be updated in SQL by using the CREATE OR REPLACE VIEW statement.

• The data in the underlying tables will be affected when the view is updated.

• Views can be updated to include new columns or filter criteria.

• Example: CREATE OR REPLACE VIEW my_view AS SELECT * FROM my_table WHERE column = 'value';

Cascade refers to the automatic propagation of changes made to a parent record to its related child records.

• Cascade is a feature in database management systems that ensures data consistency and integrity.

• It allows changes made to a parent record to be automatically reflected in its related child records.

• For example, if a parent record is deleted, all its child records will also be deleted automatically.

• Cascade can be set up for various types of actions, such as update, delete...read more

Performance tuning queries on SQL server involves optimizing query execution plans and indexing strategies.

• Use indexes to speed up query performance

• Avoid using SELECT * and only retrieve necessary columns

• Optimize joins by using appropriate join types (e.g. INNER JOIN, LEFT JOIN)

• Consider using stored procedures for frequently executed queries

• Monitor query performance using tools like SQL Server Profiler

Containers in SSIS are logical groupings of tasks and containers that define the workflow of an SSIS package.

• Containers can be used to group related tasks together and provide a clear visual representation of the package workflow.

• There are several types of containers in SSIS, including Sequence Containers, For Loop Containers, and Foreach Loop Containers.

• Sequence Containers are used to group tasks together and define the order in which they are executed.

• For Loop Containers ar...read more

Delete removes specific rows while truncate removes all rows from a table.

• Delete is a DML command while truncate is a DDL command.

• Delete can be rolled back while truncate cannot be rolled back.

• Delete is slower than truncate as it logs each row deletion while truncate does not.

• Delete can have a WHERE clause to specify which rows to delete while truncate deletes all rows.

• Delete does not reset the identity of the table while truncate resets the identity of the table.

• Example: DEL...read more