PostgreSQL中的嵌套条件条件，语法错误？

Question

我使用PostgreSQL，我想结合这两种情况，但是当我取消注释代码时，会出现语法错误。这不是一个困难的指示。我想根据条件除以或乘以获得的数字。如何输入以便编译代码？

SELECT
SUM(

CASE
    WHEN transactions.recipient_account_bill_id = recipientBill.id AND recipientBill.user_id = 2
    THEN 1
    ELSE -1
END * transactions.amount_money

/* CASE
    WHEN senderBillCurrency.id = recipientBillCurrency.id
    THEN NULL
    ELSE
        CASE
            WHEN recipientBillCurrency.base = true
            THEN /
            ELSE *
        END senderBillCurrency.current_exchange_rate
END */

) as TOTAL

FROM transactions

LEFT JOIN bills AS senderBill ON senderBill.id = transactions.sender_account_bill_id
LEFT JOIN bills AS recipientBill ON recipientBill.id = transactions.recipient_account_bill_id
LEFT JOIN currency as senderBillCurrency ON senderBillCurrency.id = senderBill.currency_id
LEFT JOIN currency as recipientBillCurrency ON recipientBillCurrency.id = recipientBill.currency_id

WHERE 2 IN (senderBill.id, recipientBill.id)

Answer 1

这是因为您试图返回运算符/或*而不是character：

CASE
    WHEN senderBillCurrency.id = recipientBillCurrency.id THEN NULL
    ELSE
        CASE
            WHEN recipientBillCurrency.base = true
            THEN '/'
            ELSE '*'
        END || senderBillCurrency.current_exchange_rate
END

Answer 2

您无法创建这样的动态SQL表达式。 CASE表达式无法返回运算符，就好像SQL是某种宏语言一样。您只能返回一个表达式。

您已经通过乘法使用1和-1使用以下方法。为什么不同时在N和1/N中使用它：

<some expression> * CASE
    WHEN senderBillCurrency.id = recipientBillCurrency.id
    THEN NULL
    ELSE CASE
        WHEN recipientBillCurrency.base
        THEN 1 / senderBillCurrency.current_exchange_rate
        ELSE senderBillCurrency.current_exchange_rate
    END 
END