Removing weight and displaying Table structure of SQL Foundation (4)

When we query through the select statement, we will find a lot of the same information, at this time we want to remove the duplicate information, what should we do?

For example, there are repetitions like the following. Here we can use distinct to repeat.

Suppose someone is working in those departments of the inquiry department. You can also query it through the following statement.

Select distinct department_id as dep_id from employees order by dep_id

Second, display the table structure

Use the DESCRIBE command to display the table structure.

DESC [RIBE] tablename

Or use the sql developer software to view

For example, we now have two tables, REGIONS and COUNTRIES, which have the following table structure

What are the countries in Europe if we want to find them? What should I do?

1. First of all, we find the Asian number in region. Through the following, we know that the Asian label is 3.

Select * from region

2. The name of the country with the tea axis region_id of 3 in the countries table will be fine (found our motherland China ^ _ ^)

Select country_id,country_name from countries where region_id=3