Mysql 如何从多个表中选择数据?
我有4个表格,我对选择数据感到非常困惑 我的4个表中有这些字段Mysql 如何从多个表中选择数据?,mysql,select,multiple-tables,Mysql,Select,Multiple Tables,我有4个表格,我对选择数据感到非常困惑 我的4个表中有这些字段 t1 -> student_id given_name user_name t2 -> school_year sem class student_id main_id t3 -> subject_id main_id t4 -> subject_id subject_name 我需要选择(给定名称、主题名称、类和主id)。怎么做 我试着这样做 SELECT t2.sc
t1 -> student_id
given_name
user_name
t2 -> school_year
sem
class
student_id
main_id
t3 -> subject_id
main_id
t4 -> subject_id
subject_name
我需要选择(给定名称、主题名称、类和主id)。怎么做
我试着这样做
SELECT t2.school_year, t2.rp_main_sem, t2.rp_main_class, t4.name, t4.subject_id, t1.given_name, t1.user_name FROM t1, t2, t3, t4 WHERE t2.school_year = 2011 AND t2.sem = 1 AND t2.class = 'ES3A' AND t3.subject_id = t4.subject_id AND t1.student_id = t2.rp_main_student_id
我想您需要这样的查询:
SELECT t1.given_name, t4.subject_name, t2.main_id
FROM t1
LEFT JOIN t2 ON t1.student_id = t2.student_id
LEFT JOIN t3 ON t2.main_id = t3.main_id
LEFT JOIN t4 ON t3.subject_id = t4.subject_id
我想您需要这样的查询:
SELECT t1.given_name, t4.subject_name, t2.main_id
FROM t1
LEFT JOIN t2 ON t1.student_id = t2.student_id
LEFT JOIN t3 ON t2.main_id = t3.main_id
LEFT JOIN t4 ON t3.subject_id = t4.subject_id
你需要加入这些表。每个表都应该有一个主键(或唯一键),以及对其他表的引用(所谓外键)
SELECT given_name , t4.subject_name, t2.class, t3.main_id
FROM t1
JOIN t2
ON t1.student_id = t2.student_id
JOIN t3
ON t2.main_id = t3.main_id
JOIN t4
ON t2.subject_id = t3.subject_id
WHERE t2.school_year = "2011"" and t2.sem = 1 --added where because of your comment
所以我们假设
- 学生表
有主键t1
student\u id
- 受试者表
有PKt4
subject\u id
是一个关联表,用于链接学生(使用他们的t2
)到具有student\u id
的类主id
是一个将主题链接到类的关联表t3
SELECT given_name , t4.subject_name, t2.class, t3.main_id
FROM t1
JOIN t2
ON t1.student_id = t2.student_id
JOIN t3
ON t2.main_id = t3.main_id
JOIN t4
ON t2.subject_id = t3.subject_id
WHERE t2.school_year = "2011"" and t2.sem = 1 --added where because of your comment
所以我们假设
- 学生表
有主键t1
student\u id
- 受试者表
有PKt4
subject\u id
是一个关联表,用于链接学生(使用他们的t2
)到具有student\u id
的类主id
是一个将主题链接到类的关联表t3
select t1.given_name, t4.subject_name, t2.class, t2.main_id
from t1
join t2 on t1.student_id = t2.student_id
join t2.main_id = t3.main_id
join t3.subject_id = t4.subject_id
这应该可以,但请告诉我们您需要什么形式的数据。你想让每个学生上一节课吗?还是每班学生?试试:
select t1.given_name, t4.subject_name, t2.class, t2.main_id
from t1
join t2 on t1.student_id = t2.student_id
join t2.main_id = t3.main_id
join t3.subject_id = t4.subject_id
尝试:
从t1、t2、t4中选择t1.given_name、t4.subject_name、t2.class、t2.main_id
在t3中,主键是main_id(或在t2中)?school_year=2011和sem=1(在where条件下)@apssiva:我在我的查询中添加了where
子句,但是如果您需要在您的问题中添加一些内容,你必须点击问题下方的edit
按钮来添加额外的细节。从t1、t2、t4中选择t1.given_name、t4.subject_name、t2.class、t2.main_id
在t3中主键是main_id(或在t2中)?school_year=2011和sem=1(在where条件下)@apssiva:我在我的查询中添加了where
子句,但是,如果您需要在问题中添加内容,则必须单击问题下方的编辑
按钮来添加额外的详细信息。