2在单个查询中分组

Question

tbl
A | B

A包含许多值。 B只包含2个值。

我希望将数据作为

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

Answer 1

希望，我理解你的问题，

试图创造同样的问题。请参考以下查询。

同一http://sqlfiddle.com/#!9/b557543/4/0

的Sqlfiddle链接

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;

Answer 2

应该如此简单：

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