Remapping/Concatenating in SQL

Question

I'm trying to reorder/group a set of results using SQL. I have a few fields (which for the example have been renamed to something a bit less specific), and each logical group of records has a field which remains constant - the address field. There are also fields which are present for each address, these are the same for every address.

id  forename    surname     address
1   John        These       Address1
2   Lucy        Values      Address1
3   Jenny       Are         Address1
4   John        All         Address2
5   Lucy        Totally     Address2
6   Jenny       Different   Address2
7   Steve       And         Address2
8   Richard     Blah        Address2

address     John    Lucy            Jenny       Steve       Richard
Address1        These   Values          Are         (null)      (null)
Address2        All     Totally         Different   And         Blah

For example: John,Lucy,Jenny,Steve and Richard are the only possible names at each address. I know this because it's stored in another location.

Can I select values from the actual records in the left hand image, and return them as a result set like the one on the right? I'm using MySQL if that makes a difference.

Answer 1

Assuming that the column headings "john", "lucy" etc are fixed, you can group by the address field and use if() functions combined with aggregate operators to get your results:

select max(if(forename='john',surname,null)) as john,
       max(if(forename='lucy',surname,null)) as lucy,
       max(if(forename='jenny',surname,null)) as jenny,       
       max(if(forename='steve',surname,null)) as steve,       
       max(if(forename='richard',surname,null)) as richard,
       address
from tablename 
group by address;

It is a bit brittle though.

There is also the group_concat function that can be used (within limits) to do something similar, but it will be ordered row-wise rather than column-wise as you appear to require.

eg.

select address, group_concat( concat( forename, surname ) ) tenants 
from tablename
group by address;

Answer 2

I'm not certain, but I think what you're trying to do is GROUP BY.

SELECT Address,Name FROM Table GROUP BY Name

if you want to select more columns, make sure they're included in the GROUP BY clause. Also, you can now do aggregate functions, like MAX() or COUNT().

Answer 3

I am not sure about the question, but from what I understand you can do:

SELECT concat(column1,column2,column3) as main_column, address from table;