跳过多个表中的内部联接mysql查询

Question

I built a large script with several inner joins working as "conditions" (instead of using WHERE clauses). As a sample:

SELECT T1.*
FROM Table1 T1
    INNER JOIN Table2 T2
        ON T1.id = T2.id
    INNER JOIN Table3 T3
        ON T2.id = T3.id
    INNER JOIN Table4 T4
        ON T1.id = T4.id

etc...

Under certain conditions I need to skip one or several inner joins. Till now, I had to duplicate the script commenting out the lines with the joins I don't need. Would it be any way to work with variables or IF clauses to skip a join, or at least a "select all" way?

Answer 1

Assuming php:

$SQL = "
SELECT T1.*
FROM Table1 T1
    INNER JOIN Table2 T2
        ON T1.id = T2.id" . ($variable1 == x ? " OR TRUE=TRUE" : "") . "
    INNER JOIN Table3 T3
        ON T2.id = T3.id" . ($variable2 == y ? " OR TRUE=TRUE" : "") . "
    INNER JOIN Table4 T4
        ON T1.id = T4.id" . ($variable3 == z ? " OR TRUE=TRUE" : "")

But I'm sure you should rather build the query dynamically:

$SQL = "
SELECT T1.*
FROM Table1 T1";

if ($variable1 == x) {
    $SQL .= " INNER JOIN Table2 T2 ON T1.id = T2.id";
}

if ($variable2 == y) {
    $SQL .= " INNER JOIN Table3 T3 ON T2.id = T3.id";
}

if ($variable3 == z) {
    $SQL .= " INNER JOIN Table4 T4 ON T3.id = T4.id";
}

etc. with all your joins.