使用子查询作为字段列

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

Answer 2

Correlated subqueries like you have in your query generally suck when it comes to performance. Since you only retrieve 100 rows, it shouldn't be too bad, but if you want it faster you have to rewrite your query.

The problem at hand can be fixed easily with:

SELECT *, unit_profit * duration AS my_calc
FROM (
   -- your query here
   -- just without "unit_profit * duration"
   -- and maybe without redundant column aliases
   ) AS sub