我有下面的查询,该查询来自于mysql中连续记录的项目数,该计数计算一个学生在一堂课中连续出现/缺席的次数。
SELECT
classlist.studentid,
student.name,
classStatus.name status,
COUNT(*) presentcnt
FROM
classlist
INNER JOIN student ON classlist.studentid=student.id
INNER JOIN classstatus ON classlist.presentid=classstatus.id
INNER JOIN (
SELECT
studentid,
max(CASE WHEN presentid=0 THEN id END) max_0,
max(CASE WHEN presentid=1 THEN id END) max_1
FROM classlist
GROUP BY studentid
) s
ON coalesce(classlist.id>least(max_0,max_1) AND classlist.id<=greatest(max_0,max_1),1) AND s.studentid=classlist.studentid
GROUP BY classlist.studentid
这按预期工作,
STUDENTID NAME STATUS PRESENTCNT
111 John Present 1
222 Kate Absent 2
333 Matt Present 5
我想扩展查询,以便有一个列显示学生是否参加了课堂。
如果我运行独立查询,则会得到想要的结果
SELECT
classlist.studentid,
student.name,
participatedStatus.name status,
COUNT(*) participatedcnt
FROM
classlist
INNER JOIN student ON classlist.studentid=student.id
INNER JOIN participatedStatus ON classlist.participatedid=participatedStatus.id
INNER JOIN (
SELECT
studentid,
max(CASE WHEN participatedid=0 THEN id END) max_0,
max(CASE WHEN participatedid=1 THEN id END) max_1
FROM classlist
group by studentid
) s
ON coalesce(classlist.id>least(max_0,max_1)
AND classlist.id<=greatest(max_0,max_1),1)
AND s.studentid=classlist.studentid
group by classlist.studentid
STUDENTID NAME STATUS PARTICIPATEDCNT
111 John Yes 1
222 Kate No 2
333 Matt Yes 2
但是我想将它们合并到一个查询中,所以我得到
STUDENTID NAME STATUS PRESENTCNT STATUS2 PARTICIPATEDCNT
111 John Present 1 Yes 1
222 Kate Absent 2 No 2
333 Matt Present 5 Yes 2
我在选择count *时如何实现这一目标感到困惑,我该如何实现呢?
我正在使用的数据样本在这个小提琴中和下面
CREATE TABLE classlist
(`id` int, `studentid` int, `subjectid` int, `presentid` int, `participatedid` int);
CREATE TABLE student
(`id` int, `name` varchar(4));
CREATE TABLE subject
(`id` int, `name` varchar(4));
CREATE TABLE classStatus
(`id` int, `name` varchar(8));
CREATE TABLE participatedStatus
(`id` int, `name` varchar(8));
INSERT INTO classlist (`id`, `studentid`, `subjectid`, `presentid`, `participatedid`)
VALUES (1, 111, 1, 1, 0), (2, 222, 3, 0, 0), (3, 333, 2, 1, 0), (4, 111, 4, 0, 0), (5, 111, 1, 1, 0), (6, 222, 3, 0, 0), (7, 333, 2, 1, 1), (8, 111, 4, 0, 0), (9, 111, 4, 0, 0), (10, 111, 4, 0, 0), (11, 111, 1, 1, 1), (12, 333, 3, 1, 0), (13, 333, 2, 1, 1), (14, 333, 3, 1, 1);
INSERT INTO student (`id`, `name`)
VALUES (111, 'John'),(222, 'Kate'),(333, 'Matt');
INSERT INTO subject (`id`, `name`)
VALUES (1, 'MATH'),(2, 'ENG'),(3, 'SCI'),(4, 'GEO');
INSERT INTO classStatus (`id`, `name`)
VALUES (0, 'Absent'), (1, 'Present');
INSERT INTO participatedStatus (`id`, `name`)
VALUES (0, 'No'),(1, 'Yes');
SELECT
studid,
studname,
status,
presentcnt,
status1,
participatedcnt FROM
(SELECT
classlist.studentid studid,
student.name studname,
classStatus.name status,
COUNT(*) presentcnt
FROM
classlist
INNER JOIN student ON classlist.studentid=student.id
INNER JOIN classstatus ON classlist.presentid=classstatus.id
INNER JOIN (
SELECT
studentid,
max(CASE WHEN presentid=0 THEN id END) max_0,
max(CASE WHEN presentid=1 THEN id END) max_1
FROM classlist
GROUP BY studentid
) s
ON coalesce(classlist.id>least(max_0,max_1) AND classlist.id<=greatest(max_0,max_1),1) AND s.studentid=classlist.studentid
GROUP BY classlist.studentid)x
JOIN
(SELECT
classlist.studentid,
student.name,
participatedStatus.name status1,
COUNT(*) participatedcnt
FROM
classlist
INNER JOIN student ON classlist.studentid=student.id
INNER JOIN participatedStatus ON classlist.participatedid=participatedStatus.id
INNER JOIN (
SELECT
studentid,
max(CASE WHEN participatedid=0 THEN id END) max_0,
max(CASE WHEN participatedid=1 THEN id END) max_1
FROM classlist
group by studentid
) s
ON coalesce(classlist.id>least(max_0,max_1)
AND classlist.id<=greatest(max_0,max_1),1)
AND s.studentid=classlist.studentid
group by classlist.studentid)y
ON x.studid=y.studentid
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