我有一个场景,我想消除我在页面上执行的查询查询的数量。假设我有这个,结果集名为filtered_table:
SELECT
col_a
,col_b
,col_c
FROM
table
where
col_a = 1
然后我有一组所有可能的结果,查询未过滤,distinct_col_a,distinct_col_b,distinct_col_c。
SELECT
distinct col_a
FROM
table
SELECT
distinct col_b
FROM
table
SELECT
distinct col_c
FROM
table
最后,对于distinct_col_a,distinct_col_b,distinct_col_c可以包含的每个值,我执行查询查询以获取filtered_table中的计数。
(for each value in distinct_col_a)
SELECT
count(col_a)
FROM
filtered_table
它很笨重,而且资源很重。我觉得应该有一些方法可以做一个汇总或者其他东西而不是for each,并且可以一次性获得这些数字,但我无法绕过它。
举个例子:
table
col_a | col_b | col_c
1 | a | x
2 | b | y
3 | c | z
3 | c | x
1 | d | x
filtered_table,使用where col_a = 1
col_a | col_b | col_c
1 | a | x
1 | d | x
我正在寻找的结果:
col_name| col_value| number results
col_a | 1 | 2
col_a | 2 | 0
col_a | 3 | 0
col_b | a | 1
col_b | b | 0
col_b | c | 0
col_b | d | 1
col_c | x | 2
col_c | y | 0
col_c | z | 0
我们可以使用unpivot
和单独聚合的时髦组合在相当紧凑的查询中创建这些结果:
declare @t table (col_a char(1), col_b char(1), col_c char(1))
insert into @t(col_a,col_b,col_c) values
('1','a','x'),
('2','b','y'),
('3','c','z'),
('3','c','x'),
('1','d','x')
select
col_name, col_value, SUM(Cnt) as results_count
from
(select *,CASE WHEN col_a = 1 THEN 1 ELSE 0 END as Cnt from @t) t
unpivot
(col_value for col_name in (col_a, col_b, col_c)) p
group by col_name,col_value
结果:
col_name col_value results_count
--------- --------- -------------
col_a 1 2
col_a 2 0
col_a 3 0
col_b a 1
col_b b 0
col_b c 0
col_b d 1
col_c x 2
col_c y 0
col_c z 0
(注意 - 这些结果与您想要的输出的顺序相同。但是目前没有ORDER BY
子句,因此无法保证)
并不是说您在WHERE
表达式中应用“CASE
子句”作为检查。如果你不能立即看到它是如何工作的,我建议你跑步
select
*
from
(select *,CASE WHEN col_a = 1 THEN 1 ELSE 0 END as Cnt from @t) t
unpivot
(col_value for col_name in (col_a, col_b, col_c)) p
首先看看unpivot
产生的影响。