sql - 将GROUP BY与AVG函数一起使用-错误的语法错误

Question

SELECT 
    AVG (CASE 
            WHEN ItemPrice LIKE '-%' 
               THEN NULL
            WHEN ItemPrice LIKE '0%' 
               THEN NULL
            ELSE CAST (ItemPrice AS FLOAT) 
         END)
GROUP BY 
    HHIncome 
FROM 
    Tacos 

SQL返回以下错误:

Error: Incorrect syntax near the keyword 'FROM'.
SQLState: S0001
ErrorCode: 156

有人可以单独解释为什么上面的语句不正确，但嵌套在下面的语句中却可以操作吗？

SELECT  
    HHIncome AS Income_Segment, 
    COUNT(Customer) AS number_of_customers, 
    AVG (CASE 
            WHEN ItemPrice LIKE '-%' THEN NULL
            WHEN ItemPrice LIKE '0%' THEN NULL
            ELSE CAST (ItemPrice AS FLOAT) 
         END) AS avg_item_price, 
    COUNT(DISTINCT(ReceiptIDDesc)) AS number_of_orders, 
    SUM(CAST(ItemPrice AS FLOAT)) AS total_spend
FROM
    Tacos 
GROUP BY 
    HHIncome;  

Answer 1

问题是GROUP BY和FROM子句的顺序。 GROUP BY必须在FROM [表名]之后。