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[英]how to select single row from one table and multiple rows from another table toghether?
[英]Add multiple rows in just one row from a single table
我怎样才能通过mysql在单行中加入多行?
范例:
学生桌
Sno.| Name | Subjects
1. | ABC | English
2. | ABC | Mathematics
3. | ABC | Science
4. | FMC | French
5. | ABC | Russian
6. | JBC | French
现在我想要这种格式
Sno.| Name | Sub1 | Sub2 | Sub3 | Sub4 |
1. | ABC | Eng | Maths| Science| Russian
2. | FMC | French| Null| Null | Null
3. | JBC | French| Null | Null | Null
我不确定该怎么做? 我应该创建视图还是表格?
我想一个观点会很好。
我同意其他答案, GROUP_CONCAT
与PHP一起分割逗号分隔的值可能是最好的方法,但是,如果出于任何其他原因需要通过Pure SQL建议的输出,则建议使用以下方法之一。
SELECT t1.Name,
MIN(t1.Subject) AS Sub1,
MIN(t2.Subject) AS Sub2,
MIN(t3.Subject) AS Sub3,
MIN(t4.Subject) AS Sub4
FROM Students t1
LEFT JOIN Students T2
ON t1.Name = t2.Name
AND t2.Subject > t1.Subject
LEFT JOIN Students T3
ON t2.Name = t3.Name
AND t3.Subject > t2.Subject
LEFT JOIN Students T4
ON t3.Name = t4.Name
AND t4.Subject > t3.Subject
GROUP BY t1.Name;
SELECT Name,
MAX(IF(RowNum = 1,Subject, NULL)) AS Sub1,
MAX(IF(RowNum = 2,Subject, NULL)) AS Sub2,
MAX(IF(RowNum = 3,Subject, NULL)) AS Sub3,
MAX(IF(RowNum = 4,Subject, NULL)) AS Sub4
FROM ( SELECT Name,
Subject,
@r:= IF(@Name = Name, @r + 1, 1) AS RowNum,
@Name:= Name AS Name2
FROM Students,
(SELECT @Name:='') n,
(SELECT @r:= 0) r
ORDER BY Name, Sno
) t
GROUP BY Name
使用以下查询,获取姓名和他/她的主题。
SELECT Name, GROUP_CONCAT(Subjects) AS List
FROM myTable
GROUP BY Name
然后,在PHP中,可以使用implode
函数打印主题。
希望这可以帮助。
尝试使用GROUP BY和GROUP_CONCAT :
SELECT Name, GROUP_CONCAT(Subjects) AS Subjects_list
FROM students_table
GROUP BY Name
然后在获取记录时使用PHP函数explode来获取存储在Subjects_list列中的不同值。
不好看!
要使用上述解决方案,您可以执行以下操作:
SELECT
Sno,
Name,
NULLIF(SUBSTRING_INDEX(SUBSTRING_INDEX(all_subjects, ',', 1), ',', -1), '') AS Sub1,
NULLIF(SUBSTRING_INDEX(SUBSTRING_INDEX(all_subjects, ',', 2), ',', -1), '') AS Sub2,
NULLIF(SUBSTRING_INDEX(SUBSTRING_INDEX(all_subjects, ',', 3), ',', -1), '') AS Sub3,
NULLIF(SUBSTRING_INDEX(SUBSTRING_INDEX(all_subjects, ',', 4), ',', -1), '') AS Sub4
FROM (
SELECT Sno, Name, CONCAT(GROUP_CONCAT(Subjects ORDER BY Sno),',,,') AS all_subjects FROM table GROUP BY name
) inner_sel
;
您的要求导致一个假设,即不得超过4个科目。 您还需要NULL
,而没有提到四个主题。
有一种请求会导致强制执行SQL代码,这通常是SQL的目的。
为了解释以上内容:我们使用GROUP_CONCAT
,然后再将其分解成碎片。 由于元素可能少于4个 ,因此我们用逗号( ',,,'
)填充。 然后,我们根据每个字符串在串联字符串中的位置将其断开,如果为空,则返回NULL
。
就美而言,不能说这是我更好的答案之一。 希望对你有帮助。
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