SELECT
c.Name,
cL.Language,
city.Name
FROM country AS c, countrylanguage AS cL, city
WHERE
c.Code = cL.CountryCode AND
c.Code = city.CountryCode AND
cL.IsOfficial = 'T' AND
city.Population > 1000000
| Name |
Language |
Name |
| Afghanistan |
Dari |
Kabul |
| Afghanistan |
Pashto |
Kabul |
| Argentina |
Spanish |
Buenos Aires |
| Argentina |
Spanish |
La Matanza |
| Argentina |
Spanish |
Córdoba |
| Armenia |
Armenian |
Yerevan |
| Australia |
English |
Sydney |
| Australia |
English |
Melbourne |
| Australia |
English |
Brisbane |
| ... |
除了给列名和计算字段起别名，SQL 也允许给表名起别名。这样做主要有两个理由：
✓ 让 SQL 写得更短；
✓ 让同一张表在一条 SELECT 中多次使用。
Oracle 不支持 AS 关键字。在 Oracle 里直接写别名，不写 AS：
FROM country c, countrylanguage cL, city
|