Question

Assume your connection from your web server to your DBA server is extremely slow, and you need to do a series of three queries to handle a single web request. Is there a way to combine the queries into one? Assume the following scenario

person.id person.name
1         James
2         Stacy

.

country.id country.name
1          USA
2          UK

.

location.person_id location.country_id
1                  1
1                  2

The web form would post two variables, ie name=”James” country=”China” and you want to do the following

• Does “James” exist, if not, insert james
• Does “China” exist, if not, insert china
• Does “James” live in “China”, if not insert relationship

ie something like

select person.id, country.id, location.person_id
from person, country, location
where
    person.name="James" and
    country.name="China" and
    person.id=location.id and country.id=location.country_id

The above query is not useful because it will return no records if either the person, or the country or the location does not exist.

I know that it would be possible to do this using a stored procedure but not all databases support stored procedures.

Answer 1

The solution is very simple

SELECT (SELECT person.id from person WHERE person.name = 'James') as Name,
       (SELECT country.id from country WHERE country.name="China") as Country,
       (SELECT location.person_id from location WHERE person.id = location.id and country.id = location.country_id and person.name = 'James' and country.name="China") as Location