[英]Have a select query with multiple where clauses return multiple result rows in one result table?
我有一个查询,例如:
SELECT COUNT(id) AS user_list FROM tbl_users
WHERE (enrolled = 1 AND age >=15 AND age < 20)
OR (enrolled = 1 AND age >=20 AND age < 25)
OR (enrolled = 1 AND age >=25 AND age < 30)
OR (enrolled = 1 AND age >=30)
我如何让它为一行和一张表中的每个where条件返回一个结果:
user_list
---------
18 --(enrolled = 1 AND age >=15 AND age < 20)
12 --(enrolled = 1 AND age >=20 AND age < 25)
22 --(enrolled = 1 AND age >=25 AND age < 30)
56 --(enrolled = 1 AND age >=30)
如前所述,您可以使用一个案例并在一个查询中执行所有操作,但是您不需要使用子查询,尽管我并不喜欢它,MySQL允许您在group by中使用列别名,所以下面的工作:
SELECT CASE WHEN (enrolled = 1 AND age >=15 AND age < 20) THEN '15-19'
WHEN (enrolled = 1 AND age >=20 AND age < 25) THEN '20-24'
WHEN (enrolled = 1 AND age >=25 AND age < 30) THEN '25-29'
WHEN (enrolled = 1 AND age >=30) THEN '30+'
ELSE 'Other'
END AS AgeRange
COUNT(id) AS user_list
FROM tbl_users
WHERE Enrolled = 1
AND Age >= 15
GROUP BY AgeRange;
注意,我仍然添加了where子句以避免扫描冗余数据。
但是,如果您缺少数据(例如,将返回一个空表),则会下降:
AGERANGE USER_LIST
15-19 0
20-24 0
25-29 0
30+ 0
如您所料。 为了解决这个问题,我将创建一个伪表以供选择,并保留您的数据:
SELECT t.Name AS Age_Range,
COUNT(u.ID) AS User_List
FROM ( SELECT '15-19' AS Name, 15 AS LowerBound, 20 AS UpperBound, 1 AS Enrolled
UNION ALL
SELECT '20-24' AS Name, 20 AS LowerBound, 25 AS UpperBound, 1 AS Enrolled
UNION ALL
SELECT '25-29' AS Name, 25 AS LowerBound, 30 AS UpperBound, 1 AS Enrolled
UNION ALL
SELECT '30+' AS Name, 30 AS LowerBound, 9999999 AS UpperBound, 1 AS Enrolled
) t
LEFT JOIN tbl_Users u
ON u.Enrolled = t.enrolled
AND u.Age >= t.LowerBound
AND u.Age < t.UpperBound
GROUP BY t.Name;
试试这个方法
create table t (list1 int,list2 int,list3 int,list4 int)
insert into t
SELECT
SUM(case when age >=15 AND age < 20 then 1 else 0 end) AS user_list1,
SUM(case when age >=20 AND age < 25 then 1 else 0 end) AS user_list2,
SUM(case when age >=25 AND age < 30 then 1 else 0 end) AS user_list3,
SUM(case when age >=15 AND age < 20 then 1 else 0 end) AS user_list4
FROM tbl_users
WHERE enrolled = 1 ;
select list1 from t union all
select list2 from t union all
select list3 from t union all
select list4 from t
以下SQL子句可能会有所帮助:
Group by
, Case
和Subqueries
...查找它们并进行处理,应该很有趣,自己弄清楚...
您可以考虑在查询中包含另一列(例如,介于15和18之间的情况,然后为1,案例...然后为2,...)作为范围,标识范围并按该范围进行分组...
这是一个示例,该示例说明如何将范围标识为子查询中的列,并在按子查询中的范围分组的查询之上:
select count(*) as Count, r as Range
from
(select
(case
when enrolled = 1 AND age >=20 AND age < 25 then 'r1'
when enrolled = 1 AND age >=25 AND age < 30 then 'r2'
end) as r
from Text)
as groups
group by r
结果如下:
范围| 计数
r1 | 10
r2 | 7
其中r1可以是您的范围,与case子句中定义的“已注册= 1 AND年龄> = 20 AND年龄<25”等相对应。
您可以使用联合:
SELECT COUNT(id) AS user_list
FROM tbl_users
WHERE (enrolled = 1 AND age >= 15 AND age < 20)
union
SELECT COUNT(id)
FROM tbl_users
where (enrolled = 1 AND age >= 20 AND age < 25)
union
SELECT COUNT(id)
FROM tbl_users
where (enrolled = 1 AND age >= 25 AND age < 30)
union
SELECT COUNT(id) FROM tbl_users where (enrolled = 1 AND age >= 30)
使用4个简单查询而不是一个复杂查询的性能应该没有问题
这很简单
select count(1),ceil(age/5)*5 from tbl_users where enrolled=1 group by ceil(age/5)
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