# Select 语法
SELECT 语句用于从数据库中选取数据。结果被存储在一个结果表中，称为结果集。
# 演示数据库Websites
| id | name | url | alexa | country |
|---|---|---|---|---|
| 1 | https://www.google.cm/ | 1 | USA | |
| 2 | 淘宝 | https://www.taobao.com/ | 13 | CN |
| 3 | 菜鸟教程 | http://www.runoob.com/ | 4689 | CN |
| 4 | 微博 | http://weibo.com/ | 20 | CN |
| 5 | https://www.facebook.com/ | 3 | USA |
# 语法
# 1. SELECT Column 实例
SELECT name,country FROM Websites;
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# 2. SELECT * 实例
SELECT * FROM Websites;
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# 3. SELECT DISTINCT 实例
SELECT DISTINCT country FROM Websites;
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# 4. WHERE 子句实例
SELECT * FROM Websites WHERE country='CN';
SELECT * FROM Websites WHERE id=1;
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# 5. AND 运算符实例
SELECT * FROM Websites
WHERE country='CN'
AND alexa > 50;
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# 6. OR 运算符实例
SELECT * FROM Websites
WHERE country='USA'
OR country='CN';
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# 7. 结合 AND & OR
SELECT * FROM Websites
WHERE alexa > 15
AND (country='CN' OR country='USA');
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# 8. ORDER BY 实例
SELECT * FROM Websites
ORDER BY alexa;
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# 9. ORDER BY DESC 实例
SELECT * FROM Websites
ORDER BY country,alexa;
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# 10. SELECT TOP 子句
SQL Server / MS Access 语法
SELECT TOP number|percent column_name(s)
FROM table_name;
MySQL SELECT LIMIT 实例
SELECT * FROM Websites LIMIT 2;
以下操作在 Microsoft SQL Server 数据库中可执行
SELECT TOP 50 PERCENT * FROM Websites;
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# 11. 列的别名实例
SELECT name AS n, country AS c
FROM Websites;
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# 12. 表的别名实例
SELECT w.name, w.url, a.count, a.date
FROM Websites AS w, access_log AS a
WHERE a.site_id=w.id and w.name="菜鸟教程";
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