union all
select count(1) from student where 歲數 = '19'
這樣得到的是兩條數據各是壹個字段
select a.c_1,b.c_2 from
(select count(1) as c_1 from student where 歲數 = '18') a,
(select count(1) as c_2 from student where 歲數 = '19') b
這樣得到的是壹條數據兩個字段