PHP + Mysql：来自第一个查询的动态表名，用于执行第二个查询

Question

I have three tables, the first is a table storing applications, the second is a table storing different online forms (different types of applications), the third is a table that stores actual form data:

    TABLE applications=========
    -applicationID (PK)
    -formID (FK)
    -formRecordID
    ====================  

    TABLE forms=========
    -formID (PK)
    -formName
    -tableName (could be 'form_businessLicense','eventLicense',etc)
    ====================

    TABLE form_businessLicense=====
    -recordID (PK)
    -dateSubmitted
    -(a whole bunch of other data)
    ===============================

"formRecordID" points to "recordID" in "form_businessLicense" or "eventLicense". Since it could reference any table, it can't be a foreign key. So instead I grab the tableName from the "forms" table, then build a query to get all the application data from, say "form_businessLicense".

So I need to get data from, say, all applications plus a bit of data from the application form filled out (ex:form_businessLicense). I'm just going to paste my code (I'm actually querying all applications in a given set of IDs):

$applications = $this->selectAll(
            "SELECT applicationID, formName, tableName, fieldIdentifier, formRecordID, dateSubmitted, DATE_FORMAT(dateSubmitted,'%c/%e/%Y') AS dateSubmittedFormat
            FROM applications AS a 
            JOIN forms AS f
            ON a.formID = f.formID
            WHERE a.applicationID IN (".$applicationIDs.")
            ORDER BY dateSubmitted ASC"
        );

        for($a=0;$a<count($applications);$a++){
            $form = $this->select("SELECT ".$applications[$a]['fieldIdentifier']." AS identifierName
                FROM ".$applications[$a]['tableName']."
                WHERE recordID = ".$applications[$a]['formRecordID']
            );
            $applications[$a]['identifierName'] = $form['identifierName'];
        }

Is there any way to merge these two queries into one so I don't have to loop over all results and run a separate query for each result? I feel like I could maybe do this with a JOIN but I'm not sure how to reference the "tableName" and "formRecordID" for use in the same SQL statement.

Answer 1

You need to apply join to three tables, and select count(PK) of third table while adding a group by clause for the PK of third table.

Note: PK used for Primary Key