Question

I have two tables in MySQL that I’m comparing with the following attributes:

tbl_fac : facility_id, chemical_id, criteria
             10      , 25         , 50
             10      , 26         , 60
             10      , 27         , 60
             11      , 25         , 30
             11      , 27         , 31 
              etc...

tbl_samp: sample_id, chemical_id, result
            5     ,    25         , 51
            5     ,    26         , 61
            6     ,    25         , 51
            6     ,    26         , 61
            6     ,    27         , 500

              etc.... 

These tables are joined by chemical_id (many-to-many—- ugh), and there are several thousand facility_id’s, and several hundred chemical_id’s for each facility_id. There are also several thousand sample_id’s, each with several hundred chemical_id’s for each sample_id. All-in-all, there are around 500,000 records in tbl_fac, and 1,000,000+ records in tbl_samp.

I’m trying to extract three groups of sample_id’s from this dataset:

Group 1: any sample_id where tbl_samp.result > tbl_fac.criteria (i.e., result exceeds criteria)

Group 2: any sample_id where tbl_samp.result < tbl_fac.criteria, AND all tbl_fac.chemical_id’s are present for that sample_id (i.e., result is less than criteria, and everything is there)

Group 3: any sample_id where tbl_samp.result < tbl_fac.criteria, BUT one or more tbl_fac.chemical_id’s are missing in the sample_id (i.e., result is less than criteria, but something is missing)

Here’s the Question: How do I get all three Groups efficiently in one query?

I’ve tried:

select * 
from tbl_fac 
left join tbl_samp 
    on tbl_fac.chemical_id = tbl_samp.chemical_id

But this only yields values that are missing for the entire dataset (not the individual samples). I have a hackish query working that uses a third table to join tbl_fac and tbl_samp, but it is so ugly I’m actually embarrassed to post it….

As always, many thanks in advance for your thoughts on this one!

Cheers,

Josh

EDIT: Ideally, I would like the sample_id and Group returned — with just one Group per sample ID (my knowledge of the data indicates that they will always fall into one of the three categories above).

Answer 1

This answer makes the assumption that there is a unique constraint on facility_id and chemical_id in tbl_fac and a unique constraint on sample_id and chemical_id in tbl_samp. What I did was build up the query one step at a time. Whether this is efficient remains to be seen.

Group 1: any sample_id where tbl_samp.result > tbl_fac.criteria (i.e., result exceeds criteria)

SELECT tbl_samp.sample_id,
       'ResultsGreaterThanCriteria' AS samplegroup
FROM   tbl_fac
       INNER JOIN tbl_samp
         ON tbl_fac.chemical_id = tbl_samp.chemical_id
WHERE  tbl_samp.result > tbl_fac.criteria
GROUP  BY tbl_samp.sample_id

Group 2: any sample_id where tbl_samp.result < tbl_fac.criteria, AND all tbl_fac.chemical_id’s are present for that sample_id (i.e., result is less than criteria, and everything is there)

SELECT tbl_samp.sample_id,
       'ResultLessThanCriteriaAndAllChems' AS samplegroup
FROM   tbl_fac
       INNER JOIN tbl_samp
         ON tbl_fac.chemical_id = tbl_samp.chemical_id
WHERE  tbl_samp.result < tbl_fac.criteria
       AND NOT EXISTS (SELECT *
                       FROM   tbl_fac tf
                              LEFT JOIN tbl_samp ts
                                ON tf.chemical_id = ts.chemical_id
                       WHERE  ts.chemical_id IS NULL
                              AND tbl_samp.sample_id = ts.sample_id)
GROUP  BY tbl_samp.sample_id

Group 3: any sample_id where tbl_samp.result < tbl_fac.criteria, BUT one or more tbl_fac.chemical_id’s are missing in the sample_id (i.e., result is less than criteria, but something is missing)

SELECT tbl_samp.sample_id,
       'ResultsLessThanCriteriaWithMissingChems' AS samplegroup
FROM   tbl_fac
       INNER JOIN tbl_samp
         ON tbl_fac.chemical_id = tbl_samp.chemical_id
WHERE  tbl_samp.result < tbl_fac.criteria
       AND EXISTS (SELECT *
                   FROM   tbl_fac tf
                          LEFT JOIN tbl_samp ts
                            ON tf.chemical_id = ts.chemical_id
                   WHERE  ts.chemical_id IS NULL
                          AND tbl_samp.sample_id = ts.sample_id)
GROUP  BY tbl_samp.sample_id 

And finally, you union all three queries together and get:

SELECT tbl_samp.sample_id,
       'ResultsGreaterThanCriteria' AS samplegroup
FROM   tbl_fac
       INNER JOIN tbl_samp
         ON tbl_fac.chemical_id = tbl_samp.chemical_id
WHERE  tbl_samp.result > tbl_fac.criteria
GROUP  BY tbl_samp.sample_id
UNION ALL
SELECT tbl_samp.sample_id,
       'ResultLessThanCriteriaAndAllChems' AS samplegroup
FROM   tbl_fac
       INNER JOIN tbl_samp
         ON tbl_fac.chemical_id = tbl_samp.chemical_id
WHERE  tbl_samp.result < tbl_fac.criteria
       AND NOT EXISTS (SELECT *
                       FROM   tbl_fac tf
                              LEFT JOIN tbl_samp ts
                                ON tf.chemical_id = ts.chemical_id
                       WHERE  ts.chemical_id IS NULL
                              AND tbl_samp.sample_id = ts.sample_id)
GROUP  BY tbl_samp.sample_id
UNION ALL
SELECT tbl_samp.sample_id,
       'ResultsLessThanCriteriaWithMissingChems' AS samplegroup
FROM   tbl_fac
       INNER JOIN tbl_samp
         ON tbl_fac.chemical_id = tbl_samp.chemical_id
WHERE  tbl_samp.result < tbl_fac.criteria
       AND EXISTS (SELECT *
                   FROM   tbl_fac tf
                          LEFT JOIN tbl_samp ts
                            ON tf.chemical_id = ts.chemical_id
                   WHERE  ts.chemical_id IS NULL
                          AND tbl_samp.sample_id = ts.sample_id)
GROUP  BY tbl_samp.sample_id