MySQL: Getting multiple rows based on the value of one row - mysql

Question

My MySQL table looks like the following:
I would like to get results where all the followings are satisfied:
form_id is 1
sort by lead_id high to low
field_number 9 for that lead_id must be 111
In summary, my query should return 9 rows. Is that possible?
Here is my attempt so far, but I really want to avoid using GROUP_CONCAT if at all possible to get a cleaner result set.
SELECT lead_id, GROUP_CONCAT(field_number, "|", value SEPARATOR "----") AS `values`
FROM lead_detail
WHERE form_id = 1
GROUP BY lead_id
ORDER BY lead_id DESC

Answer 1

If you are meaning that you want to include only rows for a lead_id if there exists a row for that lead_id with field_number=9 and value=111. And otherwise, all rows for that lead_id should be excluded...
You could do something like this:
SELECT d.id
, d.lead_id
, d.form_id
, d.field_number
, d.value
FROM ( SELECT e.lead_id
FROM lead_detail e
WHERE e.form_id = 1
AND e.field_number = 9
AND e.value = 111
GROUP BY e.lead_id
) f
JOIN lead_detail d
ON d.lead_id = f.lead_id
AND d.form_id = 1
ORDER BY d.lead_id DESC
The inline view (aliased as f) returns a distinct list of lead_id that meet specific criteria. We can reference the result from that like it were a table, and use that in a JOIN operation, to return "matching" rows from the lead_detail table. (If there's no row with value=111, field_number=9, and form_id=1 for a particular lead_id, then the inline view won't return that lead_id in the list.)
As another alternative, we could use an EXISTS predicate with a correlated subquery, but this may not perform as well:
SELECT d.id
, d.lead_id
, d.form_id
, d.field_number
, d.value
FROM lead_detail d
WHERE d.form_id = 1
AND EXISTS
( SELECT 1
FROM lead_detail e
WHERE e.form_id = 1
AND e.field_number = 9
AND e.value = 111
AND e.lead_id = d.lead_id
)
ORDER BY d.lead_id DESC
That essentially says, for every row from lead_detail run the subquery following the EXIST keyword... if the subquery returns one (or more) rows, then the EXISTS predicate returns TRUE, otherwise it returns FALSE. That subquery is "correlated" to the outer query, by a predicate in the WHERE clause, matching the lead_id to the value of lead_id from the row from the outer query.

Answer 2

The short answer is "not easily." There are a couple of ways to do this that aren't super straightforward -- probably the easiest is with a sub-query (the exact format will change depending on the exact format of your table, etc.)
SELECT lead_id, GROUP_CONCAT(field_number, "|", value SEPARATOR "----") AS `values`
FROM lead_detail
WHERE `form_id` = 1
AND `lead_id` = (SELECT `lead_id` FROM `lead_detail` WHERE `field_number` = 9 AND `value` = 111 AND `form_id` = 1) /*This is the subquery*/
GROUP BY lead_id
ORDER BY lead_id DESC
Other options include running two separate queries, one to pull the form_id (or form_ids) in question, the other to pull all data for that form_id (or those form_ids).