SELECT basics/zh

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Revision as of 14:03, 5 January 2016 by Kenlyl (talk | contribs) (Scandinavia)
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Introducing the world table of countries

這個教程介紹SQL語言。我們會使用SELECT語句。on the table France:

Summary

這個例子顯示’France法國’的人口。字串應該在'單引號'中。

修改此例子,以顯示德國 Germany 的人口。

SELECT population FROM world
  WHERE name = 'France'
SELECT population FROM world
  WHERE name = 'Germany'


Per Capita GDP

查詢顯示面積為 5,000,000 以上平方公里的國家,該國家的人口密度(population/area)。人口密度並不是 WORLD 表格中的欄,但我們可用公式(population/area)計算出來。
修改此例子,查詢面積為 5,000,000 以上平方公里的國家,對每個國家顯示她的名字和人均國內生產總值(population/area)。
SELECT name, population/area FROM world
  WHERE area > 5000000
SELECT name, gdp/population FROM world
  WHERE area > '5000000'

Scandinavia

檢查列表:單詞“IN”可以讓我們檢查一個項目是否在列表中。此示例顯示了“Luxembourg 盧森堡”,“Mauritius 毛里求斯”和“Samoa 薩摩亞”的國家名稱和人口。
顯示“Ireland 愛爾蘭”,“Iceland 冰島”,“Denmark 丹麥”的國家名稱和人口。


SELECT name, population FROM world
  WHERE name IN ('Luxembourg', 'Mauritius', 'Samoa');
SELECT name, population FROM world
  WHERE name IN ('Ireland', 'Iceland', 'Denmark');

Just the right size

Which countries are not too small and not too big? BETWEEN allows range checking (range specified is inclusive of boundary values). The example below shows countries with an area of 250,000-300,000 sq. km. Modify it to show the country and the area for countries with an area between 200,000 and 250,000.

SELECT name, area FROM world
  WHERE area BETWEEN 250000 AND 300000


SELECT name, area FROM world
  WHERE area BETWEEN 200000 AND 250000


You are ready for tutorial one:SELECT statements with WHERE.


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