假设total_sales和total_customers是integer列，则表达式total_sales / total_orders产生integer。
你需要至少铸造其中一个 *，然后才能对它们进行舍入，例如：total_sales / total_orders::numeric从除法中得到十进制结果：

round(total_sales / total_orders::numeric, 2) as SPC,
round(total_sales / total_orders::numeric, 2) as AOV

示例：

create table data
(
   total_sales integer,
   total_customers integer, 
   total_orders integer
);

insert into data values (97, 12, 7), (5000, 20, 30);

select total_sales / total_orders as int_result,
       total_sales / total_orders::numeric as numeric_result,
       round(total_sales / total_orders::numeric, 2) as SPC,
       round(total_sales / total_orders::numeric, 2) as AOV
from data;

返回：

int_result | numeric_result       | spc    | aov   
-----------+----------------------+--------+-------
        13 |  13.8571428571428571 |  13.86 |  13.86
       166 | 166.6666666666666667 | 166.67 | 166.67

select round(*column_name*, 2) from table_name;

将在postgres中给予我们舍入到2个十进制值