需要SQL查询来计算字符串的唯一组合

Question

我有一个postgres表,看起来部分如下:

Year   | Month | ...... (more columns)
"2004" | "09"  | ......
"2004" | "09"  | ......
"2004" | "09"  | ......
"2004" | "10"  | ......
"2004" | "11"  | ......
"2004" | "11"  | ......
"2004" | "12"  | ......
"2005" | "01"  | ......
"2005" | "01"  | ......

是的,这些都是字符串.不要问我为什么.

我试图弄清楚一个SQL查询,它将告诉我每年和每个月的组合有多少行.即,"2004"和"09"=> 3,"2004"和"10"=> 1,"2004"和"11"=> 2等.当我尝试做COUNT(年,月)时我得到一个错误,我不能在字符变化列上使用该函数.

Answer 1

select Year, Month, count(*)
from your_table
group by Year, Month