我可以在內部聯接子句之前包含where子句嗎

Question

我有這個代碼

$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 = '') " );

現在，我需要添加一個條件，在該條件下，用戶將提供id並且僅應選擇與id相關的東西，我才能使用此代碼

$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，您不能在內部聯接之前添加where子句。

內部聯接的語法如下：

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

您不能在內部聯接之前添加where，但是可以將條件添加到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 = '') "

或者您可以預過濾您的教職員工表，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 = '') "

編輯：

在SQL中，在單個查詢中的其他部分“上面”或“下面”的代碼將無法保證它先執行。