sql语句问题 子查询

Question

SELECT client_id,name,
**(SELECT SUM(invoice_total)FROM invoices GROUP BY client_id) AS total_sales, **
(SELECT AVG(invoice_total)FROM invoices ) AS average ,
(SELECT total_sales - average) AS difference
FROM clients；

SELECT client_id,name,
(SELECT SUM(invoice_total)FROM invoices WHERE client_id = cli.client_id) AS total_sales,
(SELECT AVG(invoice_total)FROM invoices ) AS average ,
(SELECT total_sales - average) AS difference
FROM clients cli；

数据表

正确结果

问题：为什么第一个sql语句错误 不同的是加粗的子查询
说是子查询超过一个结果 没搞懂这个报错 最终结果也应该是多个结果啊

单独执行那一句也和结果一致啊

Answer 1

(SELECT SUM(invoice_total)FROM invoices GROUP BY client_id) AS total_sales,这句查询出来的结果是聚合的表结果集，无法在行结果集中显示。如果有时间看看我当年写的sql初级入门指南对你会有帮助的