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;