The Complete Beginners Guide to SQL Fundamentals

If you set OFFSET 2, it means that the first 2 rows will be skipped and the query will start returning records from the 3rd row. Taking the example from above, to see the different tables in the employees database, we can do SHOW TABLES in employees;. The tables can be Engineering, Product, Marketing, and Sales for the basic sql queries different teams the company has. Here, we have discussed all the SQL operators in a detailed manner with examples. FULL JOIN (or explicitly FULL OUTER JOIN) returns all rows from both tables – if there’s no matching row in the second table, NULLs are returned. In this article, we’ll show you the most basic SQL queries.

Compare this to the output from the eleventh example (shown below; mind the different sorting), and you’ll see that the totals are lower. It’s logical, as the below output also includes salaries equal to or less than $3,500. This is another query that combines an aggregate function with GROUP BY. Use it whenever you want to find the minimum values for each group.

Advanced tutorials

It helps us store, manage, and retrieve that information efficiently. SQL is used to communicate with databases to retrieve and manipulate data. The list does not end here, you can perform many other database-related tasks with SQL. You will learn about all of them in detail in upcoming chapters.

The only difference is we’re ordering the output by the employee’s name descendingly. In general, this table is a list of each quarter’s sales made by every employee shown in the first table. These 20 basic queries are a must in a starter pack for every SQL beginner.

Section 6: Joining Multiple Tables

The OR operator takes in two conditions, and either one must be true in order for the row to be shown in the result. The AND operator takes in two conditions and they both must be true in order for the row to be shown in the result. This filters through and shows the results that satisfy the condition – that is, it shows only the rows of the people whose salary is more than 1500.

CROSS JOIN returns all possible combinations of rows from both tables. Going further with our guide to SQL, a database management system (or DBMS) is a computer program, just like an Internet browser or a word processor. A DBMS can configure a database as well as add, delete, and display data. Some popular DBMS programs are Oracle, PostgreSQL, MySQL, Microsoft SQL Server, and SQLite. Often you want to see query results in a certain order, such as products from the cheapest to the most expensive or product names in alphabetical order.

SQL Data Constraints

These are the fundamentals that will allow you to build solid SQL knowledge. We subtracted one quarter from another to calculate the change between the quarters. In this case, it’s the column with the fourth quarter sales minus the third quarter sales. What’s shown in the brackets can be omitted in the query and the join will work without it.

Creates a virtual table based on the result of a SQL statement. In SQL, keywords are not case-sensitive, meaning “update” is equivalent to “UPDATE“. Views makes easier for anyone to access the information they need, without getting bogged down in complicated queries. Views also act like a helpful security guard, keeping the most sensitive information in the back room, while still allowing access to what’s needed. So, if you have basic knowledge of RDBMS, then this SQL tutorial provides you with enough knowledge to master SQL.

How to compute maximum of multiple columns, aks row wise max?

The output shows all the departments and the sum of total monthly salary costs by department. When the salary is the same (green rows), the data is ordered alphabetically by last name. We might add the keyword ASC after that to sort the output ascendingly. However, that’s not mandatory, as ascending sorting is a default in SQL.

The SELECT statement points to the specific column we want to fetch data from that we want shown in the results. All tables then consist of different columns that describe the data. For example, a remote company can have multiple databases. To see a full list of their databases, we can type SHOW DATABASES; and we can zone in on the Employees database. Constraints act as rules or conditions imposed on the data, dictating what values are permissible and what actions can be taken.

Accessing Data in Two Tables Using INNER JOIN

The output shows all five employees whose sales were above $5,000 in the last three months of 2022. The output shows all the employees who had a sales decrease in the last quarter and the amount of that decrease. Of course, you can filter data in joined tables the same way as you can with only one table. Now, use WHERE to include only employees with salaries higher than $3500 in the counting.

• We use this query to select the employee’s first name, last name, and salary from the table employees.
• SQL (pronouned either as S-Q-L or Sequel) is a powerful language for querying and analyzing any amount of data in the world.
• Here is an SQL sorting the students by FullName in descending order.
• The above output was too long, and can easily run out of memory for large tables.
• All employees work in the sales division, where the department can be either Corporate or Private Individuals.

This creates a new record in the table which is a new row. Below we’ll look at some basic SQL queries along with their syntax to get started. Welcome to the learnsqlonline.org free interactive SQL tutorial. After that, you have to do the regular practice to upscale your skills. SQL functions offer an efficient and versatile approach to data analysis.

Create New Table from existing table

We learned in one of the previous examples that there are five employees in each department. This is also one of the queries we advise you to include in your SQL toolbox. It’s similar to the previous one, as it uses an aggregate function. This type of query can be used when you want to show the number of occurrences for each group.