Question

为了将各种货币的金额转换为美元，我想要使用以下查询：

SELECT 
    currency, 
    CASE currency 
      WHEN 'SAR' THEN 0.266
      WHEN 'EGP' THEN 0.113
      WHEN 'USD' THEN 1
      WHEN 'JOD' THEN 1.411
      WHEN 'GBP' THEN 1.311
      WHEN 'BHD' THEN 2.652
      WHEN 'AED' THEN 0.272
      WHEN 'EUR' THEN 1.111
      WHEN 'QAR' THEN 0.275
      WHEN 'KWD' THEN 3.315
      ELSE 0 
    END as in_usd,
    SUM(amount)*in_usd as total_in_usd
FROM 
    mytable
WHERE 
    created_at >= current_date - '7 days'::INTERVAL 
GROUP BY 
    currency

此操作失败，显示消息in_usd does not exist。

预期产出是一系列货币及其总数：

currency total_in_usd
USD      100.00
AED      59.00
GBP      143.01
...

Answer 1

将CASE表达式部分放在派生表中。对其GROUP BY做出结果：

select currency, in_usd, SUM(amount) * in_usd as total_in_usd
from
(
SELECT 
    currency, 
    CASE currency 
      WHEN 'USD' THEN 1
      WHEN 'SAR' THEN 0.266
      WHEN 'EGP' THEN 0.113
      WHEN 'USD' THEN 1
      WHEN 'JOD' THEN 1.411
      WHEN 'GBP' THEN 1.311
      WHEN 'BHD' THEN 2.652
      WHEN 'AED' THEN 0.272
      WHEN 'EUR' THEN 1.111
      WHEN 'QAR' THEN 0.275
      WHEN 'KWD' THEN 3.315
      ELSE 0 
    END as in_usd,
    amount
FROM 
    mytable
WHERE 
    created_at >= current_date - '7 days'::INTERVAL 
)
GROUP BY 
    currency, in_usd

Answer 2

你几乎拥有正确的结构 - 一个小调整应该让它工作得很好。在进行总和时乘以货币转换 -

SELECT 
    currency, 
    SUM(amount)*
      (CASE currency 
          WHEN 'SAR' THEN 0.266
          WHEN 'EGP' THEN 0.113
          WHEN 'USD' THEN 1
          WHEN 'JOD' THEN 1.411
          WHEN 'GBP' THEN 1.311
          WHEN 'BHD' THEN 2.652
          WHEN 'AED' THEN 0.272
          WHEN 'EUR' THEN 1.111
          WHEN 'QAR' THEN 0.275
          WHEN 'KWD' THEN 3.315
          ELSE 0 
      END) as total_in_usd
FROM 
    mytable
WHERE 
    created_at >= current_date - '7 days'::INTERVAL 
GROUP BY 
    currency

Answer 3

来自documentation：

在解析整个目标列表之前，无法识别别名，这意味着您无法在目标列表中的其他位置引用别名。例如，以下语句将失败：

select (qtysold + 1) as q, sum(q) from sales group by 1;
ERROR:  column "q" does not exist

您可以使用子选项修复此问题：

SELECT inner.currency, inner.in_usd, inner.sum_amount*inner.in_usd as total_in_usd
from (
    SELECT 
        currency, 
        CASE currency 
          WHEN 'SAR' THEN 0.266
          WHEN 'EGP' THEN 0.113
          WHEN 'USD' THEN 1
          WHEN 'JOD' THEN 1.411
          WHEN 'GBP' THEN 1.311
          WHEN 'BHD' THEN 2.652
          WHEN 'AED' THEN 0.272
          WHEN 'EUR' THEN 1.111
          WHEN 'QAR' THEN 0.275
          WHEN 'KWD' THEN 3.315
          ELSE 0 
        END as in_usd,
        SUM(amount) as sum_amount
    FROM 
    mytable
WHERE 
    created_at >= current_date - '7 days'::INTERVAL 
GROUP BY 
    currency) inner

使用SQL CASE / WHEN输出进行计算

3 个答案: