select AVG(RETAIL_PRICE) AVG_PRICE1,ROUND(AVG(RETAIL_PRICE),2)  AVG_PRICE2, CONVERT(AVG(RETAIL_PRICE),DECIMAL(10,2)) AVG_PRICE3
        from b_price
        GROUP BY PRODUCT_CLASSIFY,EFFECTIVE_TIME
        ORDER BY CLASSIFY_TWO,PRODUCT_CLASSIFY,COLLECATION_POINT;

1.CONVERT函式：

AVG(RETAIL_PRICE):9.316,則CONVERT(AVG(RETAIL_PRICE),DECIMAL(10,2)):9.32;

AVG(RETAIL_PRICE):51.54,則CONVERT(AVG(RETAIL_PRICE),DECIMAL(10,2)):51.54;

AVG(RETAIL_PRICE):51,則CONVERT(AVG(RETAIL_PRICE),DECIMAL(10,2)):51;

    AVG(RETAIL_PRICE):9.596,則CONVERT(AVG(RETAIL_PRICE),DECIMAL(10,2)):9.6;

AVG(RETAIL_PRICE):10.7則CONVERT(AVG(RETAIL_PRICE),DECIMAL(10,2)):10.7;

2.round函式：

AVG(RETAIL_PRICE):9.316,則ROUND(AVG(RETAIL_PRICE),2)：9.32;

AVG(RETAIL_PRICE):51.54,則ROUND(AVG(RETAIL_PRICE),2)：51.54;

AVG(RETAIL_PRICE):51,則ROUND(AVG(RETAIL_PRICE),2)：51.00;

    AVG(RETAIL_PRICE):9.596,則ROUND(AVG(RETAIL_PRICE),2)：9.60;

    AVG(RETAIL_PRICE):10.7,則ROUND(AVG(RETAIL_PRICE),2)：10.70;