如何在函數查詢中設置返回值

Question

這裏我使用mysql函數做了貨幣轉換。請在下面，

CREATE FUNCTION anycurrency_inr(book_id INT,pub_id INT) RETURNS DOUBLE 
DETERMINISTIC 
BEGIN 
DECLARE publisher_currency VARCHAR(60); 
DECLARE org_amount DOUBLE; 
DECLARE inr_amount DOUBLE; 
DECLARE convert_base DOUBLE; 
DECLARE convert_current DOUBLE; 
select publishers.currency into publisher_currency from publishers,books where publishers.user_id=pub_id and books.id=book_id; 
select publisher_currency into org_amount from books where user_id=pub_id; 
IF (publisher_currency ='inr_price') THEN 
set inr_amount=org_amount; 
ELSE 
select base_value into convert_base from currencys where base_currency='publisher_currency'; 
select current_value into convert_current from currencys where base_currency='publisher_currency'; 
set inr_amount=org_amount * (convert_current/convert_base); 
RETURN inr_amount; 
END IF; 
END 

出版商表上方的返回幣值爲publisher_currency可能爲（inr_price或doller_price或pound_price或euro_price）和我的疑問是如何在另一個查詢傳遞返回值。這裏我傳遞了currencys表中的publisher_currency值。它顯示錯誤，因爲Result包含多行。

Answer 1

被扔此錯誤的原因不止一個行由您的請求返回：

select base_value into convert_base from currencys where base_currency='publisher_currency'; 

它是不是可以插入多個值到convert_base變量