Question

SQL中count和group by 的使用

假设表table有列a和b
如果用select a,count(1) count_a from table group by a可以按a统计次数，即统计出a1，a2...an的次数
但如按照a和b统计？
即统计出a1b1, a1b2... a1bm
a2b1, a2b2... a2bm

.....

Answer 1

select a,b,COUNT(*) count_ab from test group by a,b

Answer 2

select a,b,count(1) count_a from table group by a,b

Answer 3

你的意思是
不是一条数据的a和b也要组合起来统计次数？