Dynamic transpose for unknown row value into column name on postgres - sql

Question

I have table such:
customer_number
label
value
1
address
St. John 1A
1
phone
111111111
1
email
john#cena.com
2
address
St. Marry 231A
2
phone
222222222
2
email
please#marry.me
I want new table or view so it's become:
customer_number
address
phone
email
1
St. John 1A
111111111
john#cena.com
2
St. Marry 231A
222222222
please#marry.me
but in the future there are possibility to add different label, for example there might be new label called occupation.
Important to note, I don't know the value of the label column, so it's should iterate to any value inside that column.
Is there any way to do this?

Answer 1

You can't have a "dynamic" pivot as the number, names and data types of all columns of a query must be known to the database before the query is actually executed (i.e. at parse time).
I find aggregating stuff into a JSON easier to deal with.
select customer_number,
jsonb_object_agg(label, value) as props
from the_table
group by customer_number
If your frontend can deal with JSON values directly, you can stop here.
If you really need a view with one column per attribute, you can them from the JSON value:
select customer_number,
props ->> 'address' as address,
props ->> 'phone' as phone,
props ->> 'email' as email
from (
select customer_number,
jsonb_object_agg(label, value) as props
from the_table
group by customer_number
) t
I find this a bit easier to manage when new attributes are added.
If you need a view with all labels, you can create a stored procedure to dynamically create it. If the number of different labels doesn't change too often, this might be a solution:
create procedure create_customer_view()
as
$$
declare
l_sql text;
l_columns text;
begin
select string_agg(distinct format('(props ->> %L) as %I', label, label), ', ')
into l_columns
from the_table;
l_sql :=
'create view customer_properties as
select customer_number, '||l_columns||'
from (
select customer_number, jsonb_object_agg(label, value) as props
from the_table
group by customer_number
) t';
execute l_sql;
end;
$$
language plpgsql;
Then create the view using:
call create_customer_view();
And in your code just use:
select *
from customer_properties;
You can schedule that procedure to run in regular intervals (e.g. through a cron job on Linux)

Answer 2

Generally-speaking SQL is not good at pivotting dynamically.
Here is a query that will pivot the data for you. However, it is not dynamic i.e. if a future occupation label was added then you would have to change the query. Not sure whether that is acceptable or not :
select customer_number,
max(value) filter (where label='address') as address,
max(value) filter (where label='phone') as phone,
max(value) filter (where label='email') as email
from your_customer_table
group by customer_number
Bit of an assumption that you are running Postgres 9.4 or better here so that the filter function is supported. If not then it can be re-worked using case statements :
select customer_number,
max(case when label='address' then value else null end) as address,
max(case when label='phone' then value else null end) as phone,
max(case when label='email' then value else null end) as email
from your_customer_table
group by customer_number

Answer 3

I used cross apply to solve this problem ..
Here is my query
select distinct tb9.customer_number, tb9_2.*
from Table_9 tb9 cross apply
(select max(case when tb9_2.[label] like '%address%' then [value] end) as [address],
max(case when tb9_2.[label] like '%phone%' then [value] end) as [phone],
max(case when tb9_2.[label] like '%email%' then [value] end) as [email]
from Table_9 tb9_2
where tb9.customer_number = tb9_2.customer_number
) tb9_2;