How to query multiple Left Join table when there exist null - mysql

Question

I have 20 tables (list of subjects) that has the same table structure as below.
columns
|id|student_id|result_session|result_term|result_arm|result_class|result_level|1st_test|2nd_test|exam|result_total|result_grade|result_remark|
I then have another table result_summary as below:
|id|student_id|result_score|result_average|result_term|result_session|result_level|result_class|result_arm
Minimal Query
When I write my query like so:
SELECT t2.`1st_test` AS agric1, t2.`2nd_test` AS agric2, t2.exam AS agricExam3, t2.result_total AS agricTotal,
t2.result_grade AS agricGrade, t3.`1st_test` AS basicsci1, t3.`2nd_test` AS basicsci2, t3.exam AS basicsciExam,
t3.result_total AS basicsciTotal, t3.result_grade AS basicsciGrade t2.result_remark AS agricRemark, t3.result_remark AS basicSciRemark
FROM ((result_summary AS t1 LEFT JOIN
agricultural_science AS t2 ON t1.student_id = t2.student_id) LEFT JOIN
basic_science AS t3 ON t1.student_id = t3.student_id)
WHERE (t1.student_id = '#studentID' AND t1.result_term = '#term' AND t1.result_session = '#session' AND t1.result_level = '#level' AND t1.result_class = '#resultClass') AND
(t2.student_id = '#studentID' AND t2.result_term = '#term' AND t2.result_session = '#session' AND t2.result_level = '#level' AND t2.result_class = '#resultClass') AND
(t3.student_id = '#studentID' AND t3.result_term = '#term' AND t3.result_session = '#session' AND t3.result_level = '#level' AND t3.result_class = '#resultClass')
It does not return any row. Mind you, there are data matching the query data in table t1 and t2 but not in t3.
How can I write the query to get the desire result? Thanks in advance.

Answer 1

Defining t2 and t3 table's conditions in where clause turns your left joins into INNER JOIN.
The t2 and t3 table's conditions will need to be defined in ON instead of WHERE:
select t2.`1st_test` as agric1,
t2.`2nd_test` as agric2,
t2.exam as agricExam3,
t2.result_total as agricTotal,
t2.result_grade as agricGrade,
t3.`1st_test` as basicsci1,
t3.`2nd_test` as basicsci2,
t3.exam as basicsciExam,
t3.result_total as basicsciTotal,
t3.result_grade as basicsciGrade t2.result_remark as agricRemark,
t3.result_remark as basicSciRemark
from (
(
result_summary as t1 left join agricultural_science as t2 on t1.student_id = t2.student_id
) left join basic_science as t3 on t1.student_id = t3.student_id
and (
t3.student_id = '#studentID'
and t3.result_term = '#term'
and t3.result_session = '#session'
and t3.result_level = '#level'
and t3.result_class = '#resultClass'
)
and (
t2.student_id = '#studentID'
and t2.result_term = '#term'
and t2.result_session = '#session'
and t2.result_level = '#level'
and t2.result_class = '#resultClass'
)
)
where (
t1.student_id = '#studentID'
and t1.result_term = '#term'
and t1.result_session = '#session'
and t1.result_level = '#level'
and t1.result_class = '#resultClass'
);