我有一个问题,需要在同一张表上多次进行JOIN并计算JOIN的数量。
这是数据库设置(SQL Fiddle):
CREATE TABLE state
(
[t_id] int,
[true_id] int,
[false_id] int,
[msg] varchar(32)
);
INSERT INTO state
(t_id, true_id, false_id, msg)
VALUES
(5, 6, 7, 'CASE_1'),
(10, 11, 12, 'CASE_2'),
(20, 21, 22, 'CASE_N'),
(30, 31, 32, 'FOOOO');
CREATE TABLE step
(
[id] int,
[f_id] int,
[state_type] int,
[state_value] int
);
INSERT INTO step
(id,f_id,state_type, state_value)
VALUES
(1, 5, 5, 7),
(2, 5, 5, 7),
(3, 5, 5, 6),
(4, 5, 10, 12),
(5, 5, 10, 12),
(6, 5, 10, 11),
(7, 6, 10, 12),
(8, 6, 10, 12),
(9, 7, 20, 21),
(10, 7, 20, 21),
(11, 7, 30, 32),
(12,7, 30, 31);
这是我的当前查询:
SELECT state.msg,
COUNT(state_true.true_id) AS Trues,
COUNT(state_false.false_id) AS Falses
FROM state
INNER JOIN step ON state.t_id = step.state_type
LEFT OUTER JOIN state AS state_true ON step.state_value = state_true.true_id
LEFT OUTER JOIN state AS state_false ON step.state_value = state_false.false_id
GROUP BY state.msg, step.f_id
这是我得到的内容:
msg Trues Falses
CASE_1 1 2
CASE_2 1 2
CASE_2 0 2
CASE_N 2 0
FOOOO 1 1
这是我需要的内容:
msg Trues Falses
CASE_1 1 0
CASE_2 1 1
CASE_N 1 0
FOOOO 1 0
解释:
我需要统计每个state_type和f_id组合中有多少个true和false。
有6个条目,其中f_id = 5
-> (1,2,3,4,5,6)
。如果有一个与(f_id,state_type)
相同的条目,则只应计算最后一个。因此,对于f_id 5
,条目1,2,4,5
不应计入计数,因为它们被3
和6
覆盖。
因此,在处理前6个条目后,应该有CASE_1
true => 1
false => 0
和CASE_2
true => 1
false => 0
__ 编辑 __
TABLE step:
(1, 5, 5, 7), -- do not count
(2, 5, 5, 7), -- do not count
(3, 5, 5, 6), -- this is the last entry with
-- (f_id,state_type) => (5,5) combination.
-- it overwrites the 2 previous ones => count CASE_1 true
(4, 5, 10, 12), -- do not count
(5, 5, 10, 12), -- do not count
(6, 5, 10, 11), -- count CASE_2 true
(7, 6, 10, 12), -- do not count
(8, 6, 10, 12), -- count CASE_2 false
(9, 7, 20, 21), -- do not count
(10, 7, 20, 21), -- count CASE_N false
(11, 7, 30, 32), -- do not count
(12,7, 30, 31); -- count FOOOO true