我可以在内部联接子句之前包含where子句吗

Question

我有这个代码

$q = $conn->query("SELECT facultydetails.F_NAME,Paper_title from faculty inner join facultydetails on faculty.Fac_ID = facultydetails.Fac_ID where (paper_path = 'NULL' OR paper_path = '') and  (certificate_path = 'NULL' OR certificate_path = '') and (report_path = 'NULL' OR report_path = '') " );

现在，我需要添加一个条件，在该条件下，用户将提供id并且仅应选择与id相关的东西，我才能使用此代码

$q = $conn->query("SELECT facultydetails.F_NAME,Paper_title from faculty where facultydetails.Fac_ID='$FacID' inner join facultydetails on faculty.Fac_ID = facultydetails.Fac_ID where (paper_path = 'NULL' OR paper_path = '') and  (certificate_path = 'NULL' OR certificate_path = '') and (report_path = 'NULL' OR report_path = '') " ); 

用PHP工作

Answer 1

不，您不能在内部联接之前添加where子句。

内部联接的语法如下：

SELECT column_list
FROM t1
INNER JOIN t2 ON join_condition1
INNER JOIN t3 ON join_condition2
...
WHERE where_conditions;

Answer 2

SELECT facultydetails.F_NAME,Paper_title 
from faculty 
inner join facultydetails on faculty.Fac_ID = facultydetails.Fac_ID 
where facultydetails.Fac_ID='$FacID' 
AND (paper_path = 'NULL' OR paper_path = '') and  (certificate_path = 'NULL' OR certificate_path = '') and (report_path = 'NULL' OR report_path = '')

Answer 3

您不能在内部联接之前添加where，但是可以将条件添加到on子句中，例如：

"SELECT facultydetails.F_NAME,Paper_title ".
"from faculty ".
"inner join facultydetails ".
"on (facultydetails.Fac_ID='$FacID') and (faculty.Fac_ID = facultydetails.Fac_ID) ".
"where (paper_path = 'NULL' OR paper_path = '') and  (certificate_path = 'NULL' OR certificate_path = '') and (report_path = 'NULL' OR report_path = '') "

或者您可以预过滤您的教职员工表，例如：

"SELECT facultydetails.F_NAME,Paper_title ".
"from (select * from faculty where (facultydetails.Fac_ID='$FacID')) f ".
"inner join facultydetails ".
"on f.Fac_ID = facultydetails.Fac_ID ".
"where (paper_path = 'NULL' OR paper_path = '') and  (certificate_path = 'NULL' OR certificate_path = '') and (report_path = 'NULL' OR report_path = '') "

编辑：

在SQL中，在单个查询中的其他部分“上面”或“下面”的代码将无法保证它先执行。