SQL update select语句

    student表中age段缺少数据，把student2表中的的年龄age，根据相互之间的学生名字，对应的复制过来    

UPDATE student a
SET age= (SELECT age FROM student2 WHERE name = a.name)
-- WHERE name = VALUE

    一条SQL统计总数

    

select count(1),
sum(case when money = 1 then 1 else 0 end),
sum(case when type = 1 then amount else 0 end)
from s_order;