How to compare the values for multiple rows in SQL - mysql

Question

I have a Source table as shown below..
Name Subject Marks Year
A Science 88 2015
A Social 75 2015
A Social 75 2015
A Maths 22 2015
B Social 75 2015
B Maths 50 2014
C Science 88 2015
C Social 75 2014
D Science 88 2015
D Social 75 2015
A Social 75 2015
B Maths 50 2014
and I have a requirement as below like if any student has satisfies both as in below requirements then he should be awarded as respected requirement set name in the another table B
Set1
Social 75 2015
Science 88 2015
Set2
Social 75 2015
Maths 50 2014
The expected output in the table B is as below
Name Status
A Set1
B Set2
C None
D Set1

Answer 1

try this :
SELECT NAME,
CASE WHEN SUM(SCIENCE) + SUM(SOCIAL) = 2 THEN 'GOOD' ELSE 'BAD' END AS Status
FROM (SELECT NAME,
CASE
WHEN SUBJECT = 'Science' AND MARKS = 88 AND YEAR = 2015
THEN 1 ELSE 0
END
AS SCIENCE,
CASE
WHEN SUBJECT = 'Social' AND MARKS = 75 AND YEAR = 2015
THEN 1 ELSE 0
END
AS SOCIAL
FROM A) group by Name;
SQLFiddle
[EDIT] if you have some rules to add, add a case in subquery, and update the top case :
SELECT NAME,
CASE WHEN MAX(SCIENCE) + MAX(SOCIAL) = 2 THEN 'Set1'
WHEN MAX(SOCIAL) + MAX(MATHS) =2 THEN 'Set2'
ELSE 'None'END AS Status
FROM (SELECT NAME,
CASE
WHEN SUBJECT = 'Science' AND MARKS = 88 AND YEAR = 2015
THEN 1 ELSE 0
END
AS SCIENCE,
CASE
WHEN SUBJECT = 'Social' AND MARKS = 75 AND YEAR = 2015
THEN 1 ELSE 0
END
AS SOCIAL,
CASE
WHEN SUBJECT = 'Maths' AND MARKS = 50 AND YEAR = 2014
THEN 1 ELSE 0
END AS MATHS
FROM A)x group by Name;
See the SQLFiddle

Answer 2

Try this query:
SELECT t2.Name AS Name, CASE WHEN SUM(CASE WHEN t2.Status = 'Set1' THEN 1 ELSE 0 END) >= 2 THEN 'Set1'
WHEN SUM(CASE WHEN t2.Status = 'Set2' THEN 1 ELSE 0 END) >= 2 THEN 'Set2'
ELSE 'None' END AS Status
FROM
(
SELECT DISTINCT
CASE WHEN (t.Subject = 'Social' AND t.Marks >= 75 AND t.Year = '2015') THEN 'Set1'
WHEN (t.Subject = 'Science' AND t.Marks >= 88 AND t.Year = '2015') THEN 'Set1'
WHEN (t.Subject = 'Social' AND t.Marks >= 75 AND t.Year = '2015') THEN 'Set2'
WHEN (t.Subject = 'Maths' AND t.Marks >= 50 AND t.Year = '2014') THEN 'Set2'
ELSE 'None' END AS Status,
t.Name, t.Subject, t.Marks, t.Year
FROM A t
) t2
GROUP BY t2.Name
SQLFiddle
Output:
+------+--------+
| Name | Status |
+------+--------+
| A | Set1 |
| B | Set2 |
| C | None |
| D | Set1 |
+------+--------+