SQL base de-weight and display table structure (iv)

When we query through the SELECT statement, we find a lot of the same information, and this time we want to remove the duplicate information what to do?

For example, here are the repetitions, where we can use distinct to come and go heavy

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Let's say there are people working in those departments of the query department. You can also query by using the following statement.

SELECT distinct department_id as dep_id from Employees order by DEP_ID;

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Second, the Display table structure

Use the DESCRIBE command to display the table structure.

Desc[ribe] TableName

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or use SQL Developer software to view

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Three, for example, we now have regions and countries two tables, their table structure is as follows

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What if we want to find a country in Europe? What the hell?

1, first we find the Asian number in the region, through the following we know the label of Asia is 3

SELECT * from region;

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2, we in the countries table inside the tea axis region_id 3 Country name will be possible (found our motherland China ^_^)

Select Country_id,country_name from countries where region_id=3;

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SQL base de-weight and display table structure (iv)