我可以在内部连接子句之前包含一个 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，用户将提供 id 并且只有应该选择与 id 相关的东西才能使用此代码

$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 = '') " ); 

在 php 中工作

Answer 1

您不能在内连接之前添加 where，但您可以将您的条件添加到 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 = '') "

或者您可以预先过滤您的教师表，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，在单个查询中的代码“高于”或“低于”某些其他部分并不能保证它在它之前执行。

Answer 2

不，你不能在内连接之前添加 where 子句。

内连接的语法如下：

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

Answer 3

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 = '')