mysql的where和from子查询

where 型子查询，内层查询的结果，作为外层sql的比较条件，放在where后面发挥作用
例子：

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

from 型子查询，内层查询的结果，作为外层查询的条件，放在from后面发挥作用
例子：

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