Question

How can I change from

SID Name Math English French
1   Sam  16   17      19
2   Tom  18   14      12
3   Al   90   33      2

to:

SID subject   Mark
1   Math      16
1   English   17
1   French    19
2   Math      18
2   English   14
2   French    12
3   Math      90
3   English   33
3   French    2  

using SQL (MYsql and MS Access if possible) ?

Thanks.

Answer 1

SELECT sid, 'Math' as subject, math as mark
FROM your_table
UNION ALL
SELECT sid, 'English' as subject, english as mark
FROM your_table
UNION ALL
SELECT sid, 'French' as subject, french as mark
FROM your_table

But the root cause of your problem is a wrong database design. Those subjects shouldn’t be columns in the first place and should be stored in a table very much like your desired output.

Edit

So what does it do?

SELECT sid, 'Math' as subject, math as mark
FROM your_table

Returns the sid column, a “virtual” column with the hardcoded value 'Math' that is given the name subject. As you have not stored the value 'Math' somewhere, this had to be hardcoded. Then at last it also selects the column math using the name mark instead. Note the difference between math and 'Math' – one is a column the other one a string literal because of the single quotes.

This is done for all three subjects (if you had four subjects, you’d need four parts in the UNION)

The UNION ALL combines all three SELECTs into one single query. andr solution (which has been downvoted by someone who didn’t understand it) makes this even clearer by explicitely putting that into a derived table (or inline view).

Run each SELECT on its own to see what the individual parts are doing.

The part as mark is called a “column alias” and can also be used to retrieve columns with the same name from different tables in a join and still have unique names in the result set.