使用子查詢作為字段列

Question

我有將子查詢作為字段列的查詢，但我想在其他地方使用此字段列。

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; 

如您所見，我想使用 unit_profit、customer_rate 和 vendor_rate。 如何實現？

編輯：

任何顯示加入視圖的教程？

Answer 1

您需要做的是獲取所有在蒼蠅內部完成的子查詢，並創建與 CDR 表的連接。

這將大大提高查詢的性能和響應時間。 您現在所做的是對 CDR 中的每個記錄執行 3 個查詢。 如果這個表（CDR）只有幾條記錄是可以的，但如果沒有，這可能會消耗大量的處理器、內存和磁盤 I/O。

執行“加入”並以相同格式顯示信息的技巧是加入 3 次相同的子查詢，但使用不同的別名。

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 

然后下一張桌子...

這段代碼並不完整，但我認為可以解釋您需要做什么。

謝謝！

@leo

Answer 2

在性能方面，像您在查詢中擁有的相關子查詢通常很糟糕。 由於您只檢索 100 行，因此應該不會太糟糕，但如果您希望它更快，則必須重寫您的查詢。

手頭的問題可以通過以下方式輕松解決：

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