Practical SQL, 2nd Edition: A Beginner's Guide to Storytelling with Data
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Furthermore, SQL facilitates the creation and maintenance of databases, making it an essential skill for data professionals. Here’s why SQL Is the Perfect Database Language.
The first step of using PostgreSQL is to create a database. This is done by using the createdb command as shown below: createdb db_name select FIRST_NAME, DEPARTMENT from Worker W1 where W1.DEPARTMENT='HR'; Q-38. Write an SQL query to fetch intersecting records of two tables. Interactive SQL Course - Want to learn SQL by solving quizzes and challenges after learning each concept? Enroll in our SQL Interactive Course for FREE. The following table clearly explains which type of unwanted reads the levels avoid: Isolation levels For more information regarding this, you can refer here. 17. What do you understand by command enable-debug?Each of the exercises works off a sample data set and includes an SQL editor which is just a text box with a Submit button. The exercises include a solution which shows the correct query and the output. It has a sample database feature, which shows AdventureWorks for SQL Server, and there are many other SQL versions supported: It all depends on how much you want to learn SQL. You can choose tutorials on Youtube. I tried that too. You can watch videos for hours in which someone writes queries in a notebook and mumbles something under their breath. Later, you can try to rewrite lines of code for your own project, but usually, you will not understand everything. As you can predict, it typically ends poorly, in one big chaos, and instead of learning and getting better in SQL, you just get upset, get a headache, and come to the conclusion that it was one big waste of time. If the database has been deleted successfully, then the following message would be shown: DROP DATABASE 14. What are ACID properties? Is PostgreSQL compliant with ACID?
We’ll soon show you 20 basic SQL query examples to start talking with the database. All these queries are taught in our SQL Basics course; this course will give you even more structure, examples, and challenges to solve. It has 129 interactive exercises on querying one or more tables, aggregating and grouping data, JOINs, subqueries, and set operations. Even with the 20 upcoming examples, we won’t show all the details or even all the basic-level queries. That’s why we recommend using the course as a platform for practicing the fundamentals we’ll discuss here. This one might seem more complicated, but it’s still a basic SQL query. It is used when you want to show the total values for each group but you want to include only specific rows in the sum. Query The required query is: Select * from Worker where FIRST_NAME like '%a'; Q-18. Write an SQL query to print details of the Workers whose FIRST_NAME ends with ‘h’ and contains six alphabets. We use the query to show the highest salary in each department, together with the department’s name. So let's make a comparison using none other than SQL. Here is a database containing all the options I indicated. I added columns containing features that in my opinion are the most important. They are called the options: IDWHERE first_name LIKE '___%' SELECT * /* Matches first names with exactly four characters */ FROM students We can also use the statement for removing data from multiple tables all at once by mentioning the table names separated by comma as shown below: TRUNCATE TABLE After that, we use the JOIN keyword to join the second table. We do that by referencing the table quarterly_sales in JOIN and giving it the alias ‘qs’. The % wildcard matches zero or more characters of any type and can be used to define wildcards both before and after the pattern. Search a student in your database with first name beginning with the letter K: SELECT * FROM students Range Partitioning: This method is done by partitioning based on a range of values. This method is most commonly used upon date fields to get monthly, weekly or yearly data. In the case of corner cases like value belonging to the end of the range, for example: if the range of partition 1 is 10-20 and the range of partition 2 is 20-30, and the given value is 10, then 10 belongs to the second partition and not the first.
Understanding SQL theory – including database design principles and query syntax – is essential. However, knowledge alone won't make you proficient. Actual querying experience bridges the gap between theory and application, enabling you to translate your knowledge into practical solutions. 2. Building ‘Muscle Memory’
Exercise 8: Grouping Data by Multiple Columns
One of the most interesting books about SQL I've ever read. At first glance, it looks like a guide for complete rookies. But the author raises topics that will interest advanced users." What is the main disadvantage of deleting data from an existing table using the DROP TABLE command? One of the most difficult things about learning a new programming language is setting up the right environment from scratch. Coding Ground solves that problem entirely, offering a stress-free online coding environment for all major programming languages and web technologies. That means you can hop on over there and start practicing your best SQL moves without having to lift a finger in the setup. 10. Testdome
ALTER TABLE Students /* Set multiple columns as unique */ ADD CONSTRAINT PK_Student /* Naming a unique constraint */ UNIQUE (ID, FirstName); 10. What is a Foreign Key? We write the first condition in WHERE, where we reference the salary column and set the condition that the values must be above 5,000. Then we use the OR operator, followed by the second condition. The second condition again references the salary column and uses the ‘less than’ operator to return the values below 3,000. Output first_name One-to-One - This can be defined as the relationship between two tables where each record in one table is associated with the maximum of one record in the other table.You already know how this works. The query is the same as in the previous example, but now it uses the MAX() function. Output department Working on this particular course was a great pleasure. Our team has designed interesting tasks and challenges and created a course that is perfect for practicing SQL.