How do you make an Oracle SQL query to - sql

Question

This table is rather backwards from a normal schema, and I'm not sure how to get the data I need from it.
Here is some sample data,
Value (column) Info (column)
---------------------------------------------
Supplier_1 'Some supplier'
Supplier_1_email 'foo#gmail.com'
Supplier_1_rating '5'
Supplier_1_status 'Active'
Supplier_2 'Some other supplier'
Supplier_2_email 'bar#gmail.com'
Supplier_2_rating '4'
Supplier_2_status 'Active'
Supplier_3 'Yet another supplier'
...
I need a query to find the email of the supplier which has the highest rating and is currently of status 'Active'.

Answer 1

select
m.sup_email, r.sup_rating
from
(select substr(value, 1, length(value) - length('_email') as sup_name, info as sup_email from table where value like '%_email') as m
left join
(select substr(value, 1, length(value) - length('_rating') as sup_name), info as sub_rating from table where value like '%_rating') as r on m.sup_name = r.sup_name
order by
sup_rating desc
limit
1;

Answer 2

For a single pass solution, try:
select "email" from
(select
substr("value", 1, 8 + instr(substr("value", 10, length("value")-9),'_')) "supplier",
max(case when "value" like '%_status' then "info" end) as "status",
max(case when "value" like '%_rating' then cast("info" as integer) end) as "rating",
max(case when "value" like '%_email' then "info" end) as "email"
from "table" t
where "value" like '%_rating' or "value" like '%_email' or "value" like '%_status'
group by substr("value", 1, 8 + instr(substr("value", 10, length("value")-9),'_'))
having max(case when "value" like '%_status' then "info" end) = 'Active'
order by 3 desc
) where rownum = 1
(Column names are all double-quoted as some are reserved words.)

Answer 3

Expanding on Mike's excellent suggestion:
CREATE VIEW supplier_names AS
SELECT SUBSTR(Value,INSTR(Value,'_')+1) AS supplier_id
,Info AS supplier_name
FROM the_table
WHERE INSTR(Value,'_',1,2) = 0;
CREATE VIEW supplier_emails AS
SELECT SUBSTR(Value,INSTR(Value,'_')+1,INSTR(Value,'_',1,2)-INSTR(Value,'_')-1)
AS supplier_id
,Info AS supplier_email
FROM the_table
WHERE Value LIKE '%email';
CREATE VIEW supplier_ratings AS
SELECT SUBSTR(Value,INSTR(Value,'_')+1,INSTR(Value,'_',1,2)-INSTR(Value,'_')-1)
AS supplier_id
,Info AS supplier_rating
FROM the_table
WHERE Value LIKE '%rating';
CREATE VIEW supplier_statuses AS
SELECT SUBSTR(Value,INSTR(Value,'_')+1,INSTR(Value,'_',1,2)-INSTR(Value,'_')-1)
AS supplier_id
,Info AS supplier_rating
FROM the_table
WHERE Value LIKE '%status';
The queries will perform like dogs, so I'd suggest you look into creating some virtual columns, or at least function-based indexes, to optimise these queries.