按正则表达式计算组

Question

id 
1001 
2001 
2002 
3001 
3002 
3003 

如何将id列按其第一位数1, 2, 3分组？我的意思是像下面的东西：

select count(*) from my_tbl group by expr_id_1st_digit; 

count(*) 
1 
2 
3 

Answer 1

试试这个：

SELECT Count(*) 
FROM (SELECT Substr(id, 1, 1) AS myGroup 
     FROM table1) a 
GROUP BY mygroup