mysql類型為varchar double類型字符串求和多出多個小數

-- 錯誤
SELECT
    SUM(price)
FROM
    m_user
    
-- 正確    
SELECT TRUNCATE
    ( SUM( u.price ), 2 ) 
FROM
    m_user u;

-- 正確    
SELECT 
    SUM(TRUNCATE(  u.price , 2 ) )   
FROM
    m_user u;

 

-- 正確     但是和以上誤差0.01
SELECT
    sum(cast(price as decimal(18,2)))
FROM
    m_user