2在單個查詢中的分組

Question

tbl 
A | B 

A包含許多值。 B只包含2個值。

我想要得到的數據作爲

a1 | count(b1) | count(b2) 
a2 | count(b1) | count(b2) 
.... 
an | count(b1) | count(b2) 

Answer 1

它應該是這麼簡單：

select 
a, 
count(case when b = b1 then 1 else null end) as b1, 
count(case when b = b2 then 1 else null end) as b2 
from tbl 
group by a 

Answer 2

希望能，我的理解正確的問題，

試圖創建相同問題。請參閱下面的查詢。

Sqlfiddle鏈接，同樣http://sqlfiddle.com/#!9/b557543/4/0

CREATE TABLE SO_TEST(
COL1 VARCHAR(100), 
COL2 VARCHAR(100) 
); 

INSERT INTO SO_TEST VALUES('V1','Y'); 
INSERT INTO SO_TEST VALUES('V1','N'); 
INSERT INTO SO_TEST VALUES('V2','Y'); 
INSERT INTO SO_TEST VALUES('V2','N'); 
INSERT INTO SO_TEST VALUES('V3','Y'); 
INSERT INTO SO_TEST VALUES('V4','Y'); 

select col1 , 
count(case when col2='Y' then 1 end) y_cnt, 
count(case when col2='N' then 1 end) n_cnt 
from SO_TEST 
group by col1;