Question

I have two MySQL tables. What I am trying to do is to export the information where Value 1 is 1 less than Value 2 AND where ID_1 does not have its Value 1 and Value 2 equal.

Note:

• Fields Value 1 and 2 are just integers.
• Each distinct ID_A has the same Value_2
• If there are two Value_1s that are one less than Value_2, look to Value_3 and select one that is higher
• The reason why I have two tables here is because I am going to output information from both tables
• We can write a script for this, but I need to do this in a single command for bonus points (which my instructor declared is possible)… I haven’t even started a script for this, as I don’t really know how to do that…

tableA looks like this:

ID_1  ID_2
A     A
A     B
B     A
B     B
C     A
C     B
C     C

tableB looks like this:

ID_1  ID_2  Value_1  Value_2  Value_3
A     A     2        3        NULL
A     B     3        3        NULL
B     A     4        5        NULL
B     B     7        5        NULL
C     A     7        8        98
C     B     3        8        NULL
C     C     7        8        56

The query should return this:

ID_1  ID_2
B     A
C     A

Here is what I have so far… And it keeps returning no hits, which is making me confused. I believe it is the AND clause after the first WHERE statement where I need to fix

SELECT CONCAT(...)
  INTO OUTFILE '/tmp/outfile.tab'
       FIELDS TERMINATED BY '\t'
       ESCAPED BY ''
  FROM tableA
 INNER
  JOIN tableB
    ON tableA.ID_1 = tableB.ID_1
   AND tableA.ID_2 = tableB.ID_2
 WHERE tableB.Value_1 - 1 = tableB.Value_2
   AND tableA.ID_1 !=
        ( SELECT DISTINCT
                 ID_1
            FROM tableB
           WHERE ID_1 = tableA.ID_1
             AND Value_1 = Value_2
        )
;

One final note: we issue all commands through putty, in which we can access MySQL

Answer 1

I am not 100% sure of the question, but if I get it right, the first row of tableB (Line 25 in https://i.stack.imgur.com/nQLj7.jpg) should NOT be selected, because ID_1=A has Value_1=3 in the second row (Line 26 in https://i.stack.imgur.com/nQLj7.jpg), which is the same as Value_1 of the first row (Line 25 in https://i.stack.imgur.com/nQLj7.jpg).

So you could start with something like

SELECT .... FROM
tableA NATURAL JOIN tableB
WHERE Value_1=Value_2-1
AND Value_2 NOT IN (SELECT tb.Value_1 from tableB AS tb WHERE tb.ID_1=tableB.ID_1)

which fullfills requirements #1 and #2. For requirement #3 (if there are two rows for an ID_1, chose the one with the highest Value_3), we need to sort that on Value_3 and wrap it in a superquery for grouping:

SELECT .... FROM (
SELECT * FROM
tableA NATURAL JOIN tableB
WHERE Value_1=Value_2-1
AND Value_2 NOT IN (SELECT tb.Value_1 from tableB AS tb WHERE tb.ID_1=tableB.ID_1)
ORDER BY Value_3 DESC
) AS innerview
GROUP BY Value_1,Value_2

which gives the correct answer for the test data in your example.