[英]Left join is not working fine
表tbl_students
Student_pid name email
1 waheed waheed@gmail.com
2 fareed fareed@gmail.com
表r_job_invitations
id_job email
101 waheed@gmail.com
101 fareed@gmail.com
123 waheed@gmail.com
123 fareed@gmail.com
表r_job_groups
student_id job_id group_id
1 101 1
2 101 2
1 123 1
2 123 2
从上面的三个表中,我试图让学生有条件。 这是我的查询:
$studentQuery = $conn->query("SELECT
s.student_pid,jbi.test_status
FROM `r_job_groups` jtg
LEFT JOIN tbl_students s ON jtg.student_id=s.student_pid
LEFT JOIN r_job_invitations jbi ON jbi.email=s.student_email
where jtg.group_id=".$group." and job_id=".$jobID );
从上面的查询中,获取值
$group = 1 and $jobID = 101
结果是这样的:
student_pid
1
1
2
2
实际结果应该是这样的:
student_pid
1
2
我的问题是我让学生度过美好的时光
根据查询,该结果应给2个学生,但由于作业ID不能很好地进行联接,因此结果为4个学生。
我该如何解决这个问题?
在选择中使用var时要小心,您可能会受到sql注入的影响
无论如何,您可以使用distinct来避免重复值
$studentQuery = $conn->query("SELECT DISCINCT
s.student_pid
FROM `r_job_groups` jtg
LEFT JOIN tbl_students s ON jtg.student_id=s.student_pid
LEFT JOIN r_job_invitations jbi ON jbi.email=s.student_email
where jtg.group_id=".$group." and jtg job_id=".$jobID );
或使用不同的动态表
$studentQuery = $conn->query("SELECT
s.student_pid
FROM `r_job_groups` jtg
LEFT JOIN ( select distinct student_pid
from tbl_students ) s ON jtg.student_id=s.student_pid
LEFT JOIN r_job_invitations jbi ON jbi.email=s.student_email
where jtg.group_id=".$group." and jtg.job_id=".$jobID );
然后查看您的数据样本,还尝试更改joi表的顺序
$studentQuery = $conn->query("SELECT DISTINCT s.student_pid
FROM tbl_students s
LEFT `r_job_groups` jtg s ON jtg.student_id=s.student_pid
LEFT JOIN r_job_invitations jbi ON jbi.email=s.student_email
where jtg.group_id=".$group." and job_id=".$jobID );
邀请表似乎完全没有必要-以及重复的原因。 将查询写为:
SELECT s.student_pid
FROM `r_job_groups` jtg LEFT JOIN
tbl_students s
ON jtg.student_id = s.student_pid
WHERE jtg.group_id = ".$group." and jtg.job_id = ".$jobID;
我也怀疑您想要JOIN
而不是LEFT JOIN
。
SELECT jbi.*, s.student_pid,jbi.test_status FROM
`r_job_groups` jtg LEFT JOIN tbl_students s ON jtg.student_id=s.student_pid
LEFT JOIN r_job_invitations jbi ON jbi.email=s.student_email
where jtg.group_id=1 and jtg.job_id=109 and jtg.job_id=jbi.id_job
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