How to fetch row value as a column name In Mysql - mysql

Question

I need help with below scenario. How can we get distinct values in rows as column Names dynamically?
I have data in below format..
Sno firstName Subject Marks
1 ABC Eng 10
2 PQR Hindi 20
3 LM Telgu 20
4 LM Hindi 20
5 LM Eng 39
I need output in below format.
Sno FirstName Eng Hindi Telgu
1 ABC 10 Null Null
2 PQR Null 20 Null
3 LM 39 20 20
If one more subject is added, query should be written dynamic enough to include those values too..
How can Write Query for This?

Answer 1

Hi there as Abecee told you in comment solution for your problem is pivoting table.
Here is query for your table
SELECT Sno, firstName,
SUM(CASE WHEN Subject = 'Eng' THEN Marks ELSE NULL END) AS Eng,
SUM(CASE WHEN Subject = 'Hindi' THEN Marks ELSE NULL END) AS Hindy,
SUM(CASE WHEN Subject = 'Telgu' THEN Marks ELSE NULL END) AS Telgu
FROM t1
GROUP BY firstName
ORDER BY Sno
And here is SQL Fiddle to see how it's work...
GL!
Edit:
Ok based on this bluefeet answer here is dynamics solution for your problem
SET #sql = NULL;
SELECT GROUP_CONCAT(DISTINCT
CONCAT('SUM(CASE WHEN Subject = ''',
Subject,
''' THEN Marks ELSE NULL END) AS ',
REPLACE(Subject, ' ', ''))) INTO #sql
FROM t1;
SET #sql = CONCAT('SELECT Sno, firstName, ', #sql, '
FROM t1
GROUP BY firstName
ORDER BY Sno');
PREPARE stmt FROM #sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
First part of this
SET #sql = NULL;
SELECT GROUP_CONCAT(DISTINCT
CONCAT('SUM(CASE WHEN Subject = ''',
Subject,
''' THEN Marks ELSE NULL END) AS ',
REPLACE(Subject, ' ', ''))) INTO #sql
FROM t1;
is to dynamically create this part of first query I wrote
SUM(CASE WHEN Subject = 'Eng' THEN Marks ELSE NULL END) AS Eng,
SUM(CASE WHEN Subject = 'Hindi' THEN Marks ELSE NULL END) AS Hindy,
SUM(CASE WHEN Subject = 'Telgu' THEN Marks ELSE NULL END) AS Telgu
the second part is to create prepared statement and to include dynamically created part into this
SELECT Sno, firstName,
-- here you add dynamically created part #sql
FROM t1
GROUP BY firstName
ORDER BY Sno
you do that with CONCAT in this part of code
SET #sql = CONCAT('SELECT Sno, firstName, ', #sql, '
FROM t1
GROUP BY firstName
ORDER BY Sno');
when you create that from that string you prepare statement and execute it
PREPARE stmt FROM #sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
Hope that is a little bit clear now...
Here is SQL Fiddle so you can see that you can compare both query and see how it's work..
GL!
P.S. if you have any question fill free to ask in comment bellow