mysql中group by报错记录以及子查询疑问_mysql group by报错

一、group by使用问题记录
问题：使用如下查询

SELECT id,count(*) from stu GROUP BY grade; 报错：1055 - Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'test.stu.id' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by
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原因：当使用GROUP BY语句时，SELECT列表中的所有列都必须是聚合函数的参数或者是GROUP BY语句中列出的列

二、子查询 sql语句
语句：

SELECT cust_name,cust_state,(SELECT COUNT(*) FROM orders WHERE    orders.cust_id=customers.cust_id) AS orders FROM customers  ORDER BY cust_name;
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解释：表示对于customers表的每一行都执行一次这个子查询

SELECT COUNT(*) FROM orders WHERE orders.cust_id=customers.cust_id)
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