mysql JOIN Inside a JOIN and search a group_concatenated values - mysql

Question

I cant seem to find a solution for Searching a group_concatenated value,
I have 3 table that are connected with id's
1st table have the same value with 2nd table, but no same value with 3rd,
2nd table have the same value with 1st and 3rd table,
I want to get the value inside 3rd table,
concat the values in accordance to Distinct ID's of 2nd table, display them, and be able to search
this are my tables look like
how do i search for the concatenated values
please if there's a better way, your help is much appreciated?
the query below is what i have so far
$query = $db->prepare("
SELECT
a.problem_encountered,
GROUP_CONCAT(
DISTINCT
c.full_name)
AS
fnames
FROM
maintenance_sheet_table a
LEFT JOIN
mis_incharge_table b
ON
b.mis_incharge_id = a.mis_incharge_id
INNER JOIN
users_table c
ON
c.mis_id=b.mis_id
WHERE
a.problem_encountered
LIKE
:findMe
HAVING
fnames
LIKE
:findMe
GROUP BY a.id ORDER BY a.id
");
$query->bindValue(':findMe', '%' . $keywordSearch. '%');

Answer 1

A potential answer is to filter the Users_table in a subquery. There are a number of different forms of this option, and hard to tell from your data which is required. The one I have below simply returns the users that match the search criteria.
SELECT a.problem_encountered, GROUP_CONCAT(DISTINCT innerc.full_name) AS fnames
FROM maintenance_sheet_table a
LEFT JOIN mis_incharge_table b ON b.mis_incharge_id = a.mis_incharge_id
LEFT JOIN (SELECT c.mis_id, c.full_name
FROM users_table c
WHERE c.full_name LIKE :findMe) innerc ON innerc.mis_id=b.mis_id
WHERE a.problem_encountered LIKE :findMe
GROUP BY a.id
ORDER BY a.id
However, you could also do the concatenation within the subquery if required.
SELECT a.problem_encountered, innerc.fnames
FROM maintenance_sheet_table a
INNER JOIN (SELECT mit.mis_incharge_id, GROUP_CONCAT(DISTINCT ut.full_name) AS fnames
FROM users_table ut
INNER JOIN mis_incharge_table mit ON ut.user_id = mit.user_id
GROUP BY mit.mis_incharge_id
HAVING fnames LIKE :findMe) innerc ON innerc.mis_incharge_id = a.mis_incharge_id
WHERE a.problem_encountered LIKE :findMe
GROUP BY a.id
ORDER BY a.id
Note: I agree with spencer7593, that you shouldn't use the same :findMe variable against 2 separate fields. Even if it works, to a maintenance programmer or even yourself in a few years time, will probably look at this and think that the wrong fields are being interrogated.

Answer 2

You can "search" the return from the GROUP_CONCAT() expression in the HAVING clause. As a more efficient alternative, I suspect you could use an EXISTS predicate with a subquery.
I suspect part of the problem is that your query is referencing the same bind placeholder more than one time. (In previous releases of PDO, this was a restriction, a named bind placeholder could be referenced only once.)
The workaround to this issue is to use a separate bind placeholder, e.g.
HAVING fnames LIKE :findMeToo
And then bind a value to each placeholder:
$query->bindValue(':findMe', '%' . $keywordSearch. '%');
$query->bindValue(':findMeToo', '%' . $keywordSearch. '%');
(With this issue, I don't think PDO issued a warning or error; the effect was as if no value was supplied for the second reference to the named bind placeholder. Not sure if this issue is fixed, either by a code change or a documentation update. The workaround as above, reference a bind placeholder only once within a query.)
Beyond that, it's not clear what problem you are observing.

Answer 3

Your HAVING clause should come after your GROUP BY clause
change
HAVING
fnames
LIKE
:findMe
GROUP BY a.id ORDER BY a.id
to
GROUP BY a.id
HAVING
fnames
LIKE
:findMe
ORDER BY a.id