For data engineers and data scientists, SQL is valuable expertise. All modern data warehouses as well as data or delta lakes have SQL interfaces. Understanding how an SQL query is executed can help you write fast and economical queries.
Once you understand SQL concepts like join and window, you will intuitively understand the similar APIs in Spark, Pandas, or R. After all, SQL is one of the ancient programming languages that are still best for what they were invented for (another such example is C for system programming).
SQL first appeared in 1974 for accessing data in relational databases, and its latest standard was published in 2016. It is a declarative language (i.e. a programmer specifies what to do, and not how to do it) with strong static typing.
SQL Join is one of the most common and important operations to merge data with different attributes (or columns) from different sources (or tables). In this article, you will learn about various kinds of SQL joins and best practices to write efficient joins on large tables.