Abstract: I welcome you to the fourth issue of the IEEE Communications Surveys and Tutorials in 2021. This issue includes 23 papers covering different aspects of communication networks. In particular, ...

Advanced SQL for Data Analytics. A collection of problem-solving solutions covering complex Joins, Window Functions, CTEs, and Query Optimization. Includes real-world interview questions, schema ...

Aggregate functions help turn large datasets into simple summaries used across many fields. GROUP BY and HAVING allow structured grouping and filtering of data for clearer reports. Functions like ...