SQL JOINs by Patrycja Dybka 21 Nov 2016 A SQL JOIN is a method to retrieve data from two or more database tables. This article presents a basic overview of what data from a particular SQL join will look like. A popular way of understanding SQL joins is to visualize them using Venn diagrams, so each example have corresponding Venn diagram, appropriate SELECT statement and the result table. There are a few major kinds of SQL joins: Read more SQL Subqueries by Patrycja Dybka 18 Nov 2016 The article describes what a subquery is and what these useful statements look like. We will cover basic examples with the IN, EXISTS, ANY, and ALL operators, look at subqueries in FROM and WHERE clauses, and explore the difference between correlated and nested subqueries. First, let’s start with an example database. To present some of these statements we need to have an example table and fill it with some data. Read more How to Tackle SQL NULLs: COALESCE function by Patrycja Dybka 20 Oct 2016 It's inevitable that some data in the database has no value what in SQL is represented by the NULL keyword. "No value" here is different from zero, false, or an empty string (but with exceptions! In Oracle database, NULL is the same as string of zero length). During playing with the database, treating NULLs are becoming more and more troublesome, therefore MySQL standard provides help with some of the functions, like COALESCE. Read more The Most Useful Date and Time Functions by Patrycja Dybka 21 Oct 2014 Date and time functions and formats are quite different in various databases. In this article, let's review the most common functions that manipulates dates in an Oracle database. The function SYSDATE() returns a 7 byte binary data element whose bytes represents: century, year, month, day, hour, minute, second It's important to know that select sysdate from dual in SQL*Plus gives the same result as select to_char(sysdate) from dual because SQL*Plus binds everything into character strings so it can print it. Read more S.Q.L or Sequel: How to Pronounce SQL? by Patrycja Dybka 3 Sep 2014 SQL has been around for decades and supports a many billion dollar market. However, many people still struggle with just how to pronounce the term SQL. Is it "S.Q.L" [ˈɛs kjuː ˈɛl] or is it "sequel" [ˈsiːkwəl]? SQL... Where it all started Let's start at the beginning. Relational databases came into existence with E.F. Codd's 1970 publication "A Relational Model of Data for Large Shared Data Banks." While Codd's ideas were remarkable for the time, in San Jose, California, two colleagues named Donald D. Read more SQL vs. Mongo query by Patrycja Dybka 26 Aug 2014 In recent times, NoSQL databases have become a hot topic and have gained a crowd of advocates. Indeed, when NoSQL database started to arise, SQL-to-NoSQL converters arose with them as well. But unfortunately, thanks to the code conversion possibility, SQL supporters gained unquestionable evidence that in many cases the good, old SQL is much easier to use. Especially when it comes to queries. I performed a quick Google search and found plenty of nice converter tools. Read more Can SQL Help Solve Crossword Puzzles? by Patrycja Dybka 21 Aug 2014 Everyone has solved crossword puzzles and has certainly had some problems finding an appropriate word. Thanks to SQL, it is ridiculously simple to quickly dispel your crossword doubts and give you the correct answers. Of course, Google is commonly known as a universal cure for many doubts, but handling the problem yourself is much more rewarding. Recently I came across some simple and interesting examples from Andrew Cumming's book " Read more