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:
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.
Usually we try to avoid NULLs, but sometimes we need to have a NULL instead of an actual value. When this need pops up, a helpful but little-known SQL function called NULLIF makes it possible. This post will introduce you to NULLIF and demonstrate its use in two example cases. In the article How to Tackle NULLS: The COALESCE Function , we got to know the COALESCE function. It returns the first not-null expression.
You’re probably already familiar with simple SQL queries, such as “SELECT * FROM table”. Now you are wondering what to do when you have multiple tables and you want to join them. Exactly! JOIN is the key. In this tutorial, you will learn how to connect data from multiple tables using SQL JOINs. What are SQL JOINs? Databases usually have more than one table. JOINs are an SQL construction used to join data from two or more tables.
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.
There are 250+ computer programming languages in popular use. Why should you learn SQL, or Structured Query Language? Why Should I Learn SQL? Are you interested in boosting your career? Wondering what skills are worth investing in? If you’re currently in your dream job, still searching for it, or even thinking about starting your own business, it pays to develop your technical skills. A solid technical background is highly in demand among recruiters, and it provides the necessary underpinnings for managing the IT side of your business.