SQL 条件重复时的情况

Question

我有一个名为 country 的表，它有 2 列： orderid, country_code 。

我需要在以下情况下执行以下操作：

SELECT 
    CASE
    WHEN country_code IN ('PT','IT','ES','PL','AD') THEN 'SWE'
    WHEN country_code IN ('MD','BG','BA','SI','HR','ME','RO','RS') THEN 'SEE'
    WHEN country_code IN ('CI','GH','MA','NG','UG','KE','TN') THEN 'AFRICA'
    WHEN country_code IN ('CI','GH','NG','UG','KE','TN') THEN 'SSA' 
    WHEN country_code IN ('UA','BY','GE','KZ','KG','AM') THEN 'ECA'
    END AS region,
    COUNT(DISTINCT orderid) AS amount_of_orders
FROM country
GROUP BY 1

但是，当我运行代码时，区域 SSA 没有出现，因为 (AFRICA) 之前的条件使用的是 SSA 的国家（SSA 与 AFRICA 相同，但没有 MA） 。

我怎样才能获得完整的非洲和 SSA 订单量？

关系数据库：亚马逊红移

编辑：这是我现在的桌子：

SWE 200
SEE 500
AFRICA 350
SSA 0 <--- (it doesn't appear because the conditions were met by AFRICA region)
ECA 200

我需要以下内容：

SWE 200
SEE 500
AFRICA 350 --> (MA represent 150 orders)
SSA 200 --> (sames as AFRICA, but without MA)
ECA 200

Answer 1

您可以定义一个包含所有国家代码及其对应区域的公用表表达式 (CTE)，然后将其与您的数据连接起来。

WITH regions AS 
( 
            SELECT CAST('PT,IT,ES,PL,AD' AS VARCHAR) AS country_codes, 'SWE' AS region_code
  UNION ALL SELECT CAST('MD,BG,BA,SI,HR,ME,RO,RS' AS VARCHAR) AS country_codes, 'SEE' AS region_code
  UNION ALL SELECT CAST('CI,GH,MA,NG,UG,KE,TN' AS VARCHAR) AS country_codes, 'AFRICA' AS region_code
  UNION ALL SELECT CAST('CI,GH,NG,UG,KE,TN' AS VARCHAR) AS country_codes, 'SSA' AS region_code
  UNION ALL SELECT CAST('UA,BY,GE,KZ,KG,AM' AS VARCHAR) AS country_codes, 'ECA' AS region_code
)
SELECT 
    regions.region_code AS region,
    COUNT(DISTINCT orderid) AS amount_of_orders
FROM country  
     INNER JOIN regions ON STRPOS(regions.country_codes, country.country_code) > 0
GROUP BY regions.region_code;

演示： http://sqlfiddle.com/#!17/9eecb/101807

Answer 2

你想连接字符串。 由于缺少一些 CONCAT_WS function 跳过空值，只需在每个区域使用逗号并在最后相应地修剪字符串。

SELECT
  TRIM(',' FROM
    CASE WHEN country_code IN ('PT','IT','ES','PL','AD') THEN ',SWE' ELSE '' END ||
    CASE WHEN country_code IN ('MD','BG','BA','SI','HR','ME','RO','RS') THEN ',SEE' ELSE '' END ||
    CASE WHEN country_code IN ('CI','GH','MA','NG','UG','KE','TN') THEN ',AFRICA' ELSE '' END ||
    CASE WHEN country_code IN ('CI','GH','NG','UG','KE','TN') THEN ',SSA' ELSE '' END ||
    CASE WHEN country_code IN ('UA','BY','GE','KZ','KG','AM') THEN ',ECA' ELSE '' END
  ) AS regions,
  COUNT(DISTINCT orderid) AS amount_of_orders
FROM country
GROUP BY regions
ORDER BY regions;

更新

您已完全更改您的请求。 您回答说您想要一个包含区域列表的列（例如“AFRICA,SSA”），但现在您表明您想要每个区域一行。 请不要对您的请求进行此类根本性更改。 但是，您现在想要一个单一区域查询的联合：

SELECT 'SWE' AS region, COUNT(DISTINCT orderid) AS amount_of_orders
FROM country
WHERE country_code IN ('PT','IT','ES','PL','AD')
UNION ALL    
SELECT 'SEE' AS region, COUNT(DISTINCT orderid) AS amount_of_orders
FROM country
WHERE country_code IN ('MD','BG','BA','SI','HR','ME','RO','RS')
UNION ALL    
SELECT 'AFRICA' AS region, COUNT(DISTINCT orderid) AS amount_of_orders
FROM country
WHERE country_code IN ('CI','GH','MA','NG','UG','KE','TN')
UNION ALL    
SELECT 'SSA' AS region, COUNT(DISTINCT orderid) AS amount_of_orders
FROM country
WHERE country_code IN ('CI','GH','NG','UG','KE','TN')
UNION ALL    
SELECT 'ECA' AS region, COUNT(DISTINCT orderid) AS amount_of_orders
FROM country
WHERE country_code IN ('UA','BY','GE','KZ','KG','AM');