mysql的where和from子查詢

where 型子查詢，內層查詢的結果，作爲外層sql的比較條件，放在where後面發揮作用
例子：

SELECT age,name,id from test.a where age  = (SELECT MAX(age) from test.a where 1)

from 型子查詢，內層查詢的結果，作爲外層查詢的條件，放在from後面發揮作用
例子：

SELECT id,name,age from (SELECT * from test.b where name = 'deng1' ) as q WHERE age = 1