SQL Tutorial: Filtering and ordering

Want to learn more? Take the full course at https://learn.datacamp.com/courses/data-driven-decision-making-with-sql at your own pace. More than a video, you'll learn hands-on coding & quickly apply skills to your daily work. --- A main part of querying data is to filter those records which are relevant for a certain research question. For future applications, it is also essential to bring tables in a particular order. When a WHERE clause is added to the SQL statement, certain rows of a table are selected where a selection condition holds. This example query selects all columns from the customers table only for customers from Italy by using `WHERE country = 'Italy'`. We can see the first few selected rows of the resulting table. Several operators can be used in the WHERE clause, such as comparison operators, which compare the value of a column to a given value. These can check if the values are equal or not or whether one is greater or less than the other. Then there is the BETWEEN operator, the IN operator, and the NULL operator. Let's illustrate this with some examples. Here are examples of comparison operators. In the first example, we select all columns from `movies` where the genre is not Drama. In the second example we select those movies with a renting price greater than or equal to 2. Let's now look at the BETWEEN operator. We select all columns of `customers` where the date when the account was created is between the beginning of January and end of September 2018. The first of January and the 31st of September are included in the selection. Pay special attention to the way dates are used here. Dates can be compared if they are before or after a given date but it is necessary to use single quotation marks as for strings. Unless explicitly specified otherwise in the settings, only single quotes are accepted in most SQL flavors. Using double quotes will give an error in Postgres. With the IN operator we can compare the values of a column to mult