Using SubQuery as Field Column

Question

I have the query which has subquery as field column but i want to use this field column in other place.

SELECT c.country_code                                                    AS 
       country_code, 
       c.dial_code                                                       AS 
       dial_code, 
       (SELECT r.destination 
        FROM   region r 
        WHERE  r.country_code = c.country_code 
               AND r.dial_code = c.dial_code)                            AS 
       destination, 
       c.start_time, 
       c.duration, 
       c.call_type, 
       c.customer_prefix                                                 AS 
       customer_prefix, 
       c.vendor_prefix                                                   AS 
       vendor_prefix, 
       (SELECT Round(r.rate, 3) 
        FROM   rate r 
               INNER JOIN region re 
                       ON r.region_id = re.id 
               INNER JOIN account_prefix ap 
                       ON r.account_prefix_id = ap.id 
        WHERE  re.country_code = c.country_code 
               AND re.dial_code = c.dial_code 
               AND ap.prefix = c.customer_prefix 
               AND ap.prefix_type = 0)                                   AS 
       **customer_rate**, 
       (SELECT Round(r.rate, 3) 
        FROM   rate r 
               INNER JOIN region re 
                       ON r.region_id = re.id 
               INNER JOIN account_prefix ap 
                       ON r.account_prefix_id = ap.id 
        WHERE  re.country_code = c.country_code 
               AND re.dial_code = c.dial_code 
               AND ap.prefix = c.vendor_prefix 
               AND ap.prefix_type = 1)                                   AS 
       **vendor_rate**, 
       (SELECT Round(r.rate, 3) 
        FROM   rate r 
               INNER JOIN region re 
                       ON r.region_id = re.id 
               INNER JOIN account_prefix ap 
                       ON r.account_prefix_id = ap.id 
        WHERE  re.country_code = c.country_code 
               AND re.dial_code = c.dial_code 
               AND ap.prefix = c.customer_prefix 
               AND ap.prefix_type = 0) - (SELECT Round(r.rate, 3) 
                                          FROM   rate r 
                                                 INNER JOIN region re 
                                                         ON r.region_id = re.id 
                                                 INNER JOIN account_prefix ap 
                                                         ON r.account_prefix_id 
                                                            = ap.id 
                                          WHERE 
       re.country_code = c.country_code 
       AND re.dial_code = c.dial_code 
       AND ap.prefix = c.vendor_prefix 
       AND ap.prefix_type = 1) AS **unit_profit**, 
       unit_profit * duration 
FROM   cdr c 
LIMIT  100; 

As you can see, I want to use the unit_profit, customer_rate, and vendor_rate. How to achieve it ?

EDIT:

Any tutorial that showing join on view ?

Answer 1

What you need to do is to take all those subqueries done inside the flieds, and create a join with the CDR table.

This will greatly improve the performance of the query and response time. What you are doing now is executing 3 queries for each for the records at CDR. Ff this table (CDR) have just a few records is fine, but if not this could consume lot of processor, memory and disk I/O.

The trick to do the "join" and show the info in the same format is to join 3 times the same subquery but with a different alias.

select  c.country_code, customer_rate_table.customer_rate 
from CDR c
left outer join on ( SELECT Round(r.rate, 3) customer_rate , re.country_code, 
                       re.dial_code, re.dial_code, ap.prefix  
               FROM   rate r 
               INNER JOIN region re 
                       ON r.region_id = re.id 
               INNER JOIN account_prefix ap 
                       ON r.account_prefix_id = ap.id 
               WHERE ap.prefix_type = 1
        
) customer_rate_table
ON  customer_rate.country_code = c.country_code 
AND customer_rate.dial_code = c.dial_code 
AND customer_rate.prefix = c. customer_prefix 
left outer join on ( {Same as above but with the right fields} ) vendor_rate_table
ON  vendor_rate_table.country_code = c.country_code 
AND vendor_rate_table.dial_code = c.dial_code 
AND vendor_rate_table.prefix = c.vendor_prefix 

and then the next table...

This code is not complete but I think gives an explanation on what you need to do.

Thanks!

@leo