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15 Mar 2017
Understanding the Use of NULL in SQL Three-Valued Logic
NULLs are necessary in relational databases, and learning to use them is fundamental to SQL success. However, NULLs should also be handled with care, as we explain in this post. In relational databases, we don’t always have a value to put in a column. For example, suppose we have a table called “persons” that has “first_name”, “last_name”, “birth_date” and “marriage_date” columns. What value will we store in the “marriage_date” column for single persons?
14 Mar 2017
Complete SQL Practice for Interviews
Congratulations! Your SQL skills were strong enough to get you that job interview! Now, if you only knew what SQL questions and practical exercises a recruiter might ask you to do… This article is meant as a SQL practice for interviews. I’ll help you prepare for the SQL and database aspects of your job interview. In a previous article, I explained how can you boost your career by learning SQL.
1 Mar 2017
SQL Development? Structured Query Language and Apps
You know about using SQL with databases. How does SQL fit in with app development? Is there anything like SQL development? In this post, we look at the app development process, how it intersects with modeling a database, and what developers can do with SQL outside of their app. Obviously, the beginning of this process is defining your app — what it does, who it is for, how it will function and look, etc.
21 Feb 2017
The Complete Beginner’s Guide to SQL Fundamentals
LearnSQL.com is a great place to learn SQL. If you’re a complete beginner, it’s best to have an overview of what SQL is, what a database is, and how they work together. In this article, you’ll find a complete guide to SQL fundamentals. SQL Fundamentals: Database Let’s begin our guide to SQL with basic definitions. You might have already heard that SQL is used with databases. What exactly is a database?
16 Feb 2017
Finding the Perfect SQL Job
So you have some SQL skills and you're looking for a job that will use them. What are your options? SQL is everywhere, and there's a huge demand for people with database management skills. This is especially the case when companies start implementing Big Data solutions and strategies. There's no arguing that SQL is a must-have skill. If you're already proficient, how can you put your expertise to practical use in the job market?
16 Feb 2017
A Day in the Life of a SQL Developer
What is a SQL developer? And what does a SQL developer do? Describing a “typical” day for a SQL developer is not easy. When your daily work is using various technologies to create interesting database-oriented products, very few days are alike! Each day brings a new and intriguing challenge. Nevertheless, I’ll have a go at explaining what everyday things a SQL developer might do. Morning: Arrive at Work What does a SQL developer do after arriving at the office?
25 Jan 2017
Jeffrey J. Keller
Grouping, Rolling, and Cubing Data
The first two articles in this series highlighted SQL Server's ability to organize data into user-defined windows and its aggregate functions. Part 3 will focus on other methods of aggregating and organizing data using built-in SQL Server features – specifically, its grouping functions. For consistency, the same base data will be used as in the first two parts of this series. CREATE TABLE WindowTable (WindowID INT IDENTITY, House Varchar(32), FullName Varchar(64), PhysicalSkill Decimal(4, 2), MentalSkill Decimal (4, 2)) GO
24 Jan 2017
Performing Calculations on Date- and Time-Related Values
Relational databases support several date and time data types. In this article, we'll look at several arithmetic operations we can do on these types. These operations are logical and understandable, even for the beginning SQL coder. Let's first briefly explain the main data types used for dates and times. Keep in mind that data types may differ by database engine, so check your database documentation for specifics before you start working with them.
18 Jan 2017
Getting the Hang of the GROUP BY Clause
GROUP BY is an important part of the SQL SELECT statement. But new SQL coders can run into some problems when this clause is used incorrectly. Here’s how to avoid those issues. You’re learning SQL. You know how to SELECT some data FROM a table and how to filter the data with a WHERE clause. You can process the data using aggregate functions (MIN, MAX, SUM, AVG, and others). But when you’re dealing with a lot of data, you may need to narrow it down even more.
3 Jan 2017
How to Recognize SQL Text Data Type
How can you store textual information in database tables? Thanks to this post, you’ll learn the characteristics of every text data type in SQL Note: This post is intended for readers familiar with SQL data definition language (DDL) and the DDL CREATE statement. To learn more about DDL, check out LearnSQL.com. Most data types are classified as NUMERIC, CHARACTER, or DATE. In this post, we’re going to focus on each CHARACTER or text data type in SQL.