It is a ready-made script that provides users with all the necessary features and functionalities like Binance. Only dive into this one if you're feeling confident using SQL and want to explore joins in more depth.A Binance clone script is an exact replica of the popular cryptocurrency exchange platform, Binance. Joining Multiple Tables: This section is more advanced. Filtering Data: More good information on the basics. Querying Data: This section has some good information on the basics of querying. To explore PostgreSQL further, check out the following tutorial. To return results 11-20, our query would look like this: SELECT * FROM albums LIMIT 10 OFFSET 10 Specifically, OFFSET skips a specified number of rows before returning results. What if we wanted to return the next ten? We can use OFFSET to do that. This will return just the first ten rows in the albums table. We can always chain a LIMIT clause to a SELECT statement like this: SELECT * FROM albums LIMIT 10 Then, if the user were to click on page 2, they'd get the next ten results. It's more common to paginate the results, which means we might return just the first ten results. However, in a real-world application, we generally wouldn't want to return all the results in our database. Limiting ResultsĬurrently, our databases are small. For example, which book is due next or what is the order of trains leaving the station today?įor more information on sorting, check the ORDER BY documentation. This can be very useful for organizing numbers and dates as well. We can also do this in reverse alphabetical order: SELECT * FROM albums ORDER BY name DESC To do so alphabetically, we can do the following: SELECT * FROM albums ORDER BY name ASC SQL can do it much faster and has built-in functionality for it. Let's say we wanted to list all our Albums alphabetically. This would still return "A Love Supreme."įor more information on LIKE and ILIKE, check the LIKE documentation. We could also use the ILIKE, which is case-insensitive: SELECT * FROM albums WHERE name ILIKE '%love%' In plain English, %Love% means "look for a name that includes 'Love' anywhere inside it, regardless of the number of characters that come before or after the phrase." The % specifically is used to match any number of characters. This uses % as a wildcard much like other regular expressions. For instance, the following query would find "A Love Supreme": SELECT * FROM albums WHERE name LIKE '%Love%' We could create a search function in our record store application by using PostgreSQL's LIKE operator. Writing tests and creating Ruby methods is relatively straightforward and is good practice. We will omit these steps because this lesson is designed to improve SQL knowledge. Keep in mind that you will need to wrap these queries with Ruby methods and test them. You are also welcome to include bonus queries in this course section's independent project as well. In addition to providing other career opportunities, understanding SQL can help us better understand ActiveRecord and similar tools used with other languages.Īll of the content included in this lesson is optional but you are encouraged to explore some of these queries in your multi-day project. That being said, it's still useful to have a strong foundation with SQL. Because ActiveRecord creates a wrapper around our SQL statements, we'll be using ActiveRecord syntax instead of SQL syntax to make queries. However, this isn't an IT or database administration course and we will be moving on to Rails and ActiveRecord in the next course section. We could easily spend a month covering all that PostgreSQL has to offer. SQL databases are an extremely powerful tool.
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