SQL: multi valued attributes

Question

I created a table that contains information about a company. One attribute is their telephone number. A company can have many telephone numbers.

How do I create mul

Answer 1

There're some possibilities in different implementations of RDBMS.

For example, in PostgreSQL you can use array or hstore or even JSON (in 9.3 version):

create table Company1 (name text, phones text[]);

insert into Company1
select 'Financial Company', array['111-222-3333', '555-444-7777'] union all
select 'School', array['444-999-2222', '555-222-1111'];

select name, unnest(phones) from Company1;

create table Company2 (name text, phones hstore);

insert into Company2
select 'Financial Company', 'mobile=>555-444-7777, fax=>111-222-3333'::hstore union all
select 'School', 'mobile=>444-999-2222, fax=>555-222-1111'::hstore;

select name, skeys(phones), svals(phones) from Company2    

sql fiddle demo

You can also create indexes on these fields - https://dba.stackexchange.com/questions/45820/how-to-properly-index-hstore-tags-column-to-faster-search-for-keys, Can PostgreSQL index array columns?

In SQL Server, you can use xml datatype to store multivalues:

create table Company (name nvarchar(128), phones xml);

insert into Company
select 'Financial Company', '555-444-7777111-222-3333' union all
select 'School', '444-999-2222555-222-1111'

select
    c.name,
    p.p.value('@type', 'nvarchar(max)') as type,
    p.p.value('.', 'nvarchar(max)') as phone
from Company as c
    outer apply c.phones.nodes('phone') as p(p)

sql fiddle demo

You can also create xml indexes on xml type column.