Difference: SQL UNION vs UNION ALL ? UNION and UNION ALL are both used to retrieve records from multiple tables. This article will detail the differences between the two, allowing you to make the best choice for each unique scenario. You can use SQL’s UNION and UNION ALL commands to get data from multiple tables in your database. It’s a common use case, considering that most databases have many tables. Both UNION and UNION ALL are known as set operators. In SQL, set operators combine the results of two or more queries into a single result. You can read more about set operators in this article . When comparing UNION vs. UNION ALL , there is one major difference: UNION only returns unique UNION ALL returns all records, including duplicates. If you feel like you would benefit from a well-structured, comprehensive course that covers foundational SQL, consider this SQL...
https://towardsdatascience.com/everything-you-need-to-know-about-regular-expressions-8f622fe10b03 Everything you need to know about Regular Expressions What is a Regular Expression? On an abstract level a regular expression, regex for short, is a shorthand representation for a set. A set of strings. Say we have a list of all valid zip codes. Instead of keeping that long and unwieldy list around, it’s often more practical to have a short and precise pattern that completely describes that set. Whenever you want to check whether a string is a valid zip code, you can match it against the pattern. You’ll get a true or false result indicating whether the string belongs to the set of zip codes the regex pattern represents. Let’s expand on the set of zip codes. A list of zip codes is finite, consists of rather short strings, and is not particularly challenging computationally. What about the set of strings that end in .csv ? Can be quite useful when looking for data files. This set ...