SELECT
Name
FROM country
WHERE Code IN (
SELECT CountryCode
FROM countrylanguage
WHERE Language = 'Russian'
)
| Name |
| Azerbaijan |
| Belarus |
| Estonia |
| Finland |
| Georgia |
| Israel |
| Kazakstan |
| Kyrgyzstan |
| Lithuania |
| ... |
| 执行这个查询时，先运行子查询：
SELECT CountryCode FROM countrylanguage WHERE Language = 'Russian' 它的结果再传给外层查询的 WHERE 子句。 |