Data Engineered

  Difference between OLAP and OLTP   Key differences: OLAP vs. OLTP The primary purpose of online analytical processing (OLAP) is to analyze aggregated data, while the primary purpose of online transaction processing (OLTP) is to process database transactions. You use OLAP systems to generate reports, perform complex data analysis, and identify trends. In contrast, you use OLTP systems to process orders, update inventory, and manage customer accounts. Other major differences include data formatting, data architecture, performance, and requirements. We’ll also discuss an example of when an organization might use OLAP or OLTP. Requirements OLAP systems act like a centralized data store and pull in data from multiple data warehouses, relational databases, and other systems. Storage requirements measure from terabytes (TB) to petabytes (PB). Data reads can also be compute-intensive, requiring high-...

Common Table Expression(CTE): A CTE is temporary result set that you define within a WITH clause. It can be referenced multiple times within the main Query Syntax: WITH cte_name As (  Select col1, col2 from table_name where <Condition> ) Select col1, col2 from cte_name where <condition> SubQueries: Subquery is nested query within the main query Syntax: Select col1, col2 from table_name where col3 in (select col3 from other_table where condition)   🔑 Key Differences: 🔹 Readability: CTEs are cleaner and easier to maintain in complex queries. 🔹 Re-usability: CTEs can be referenced multiple times, while subqueries are one-time use. 🔹 Recursion: CTEs shine in recursive queries, which subqueries don’t support. 💼 When to Use: 🔹 Use CTEs when you need to reuse logic, improve readability, or perform recursive operations. 🔹 Use Subqueries for simpler tasks where reuse isn’t needed.