需求：

1. 现有订单最早出账账期；

软件access；（测试MySQL也会报错）
单表查询，
需要嵌套子查询遇到了错误，

错误代码：子查询没有赋予别名，

-- 查询订单首次出现的账期(错误代码)
SELECT
	code1,
	month1,
	crm_bill_order_info.server_start_date 
FROM
	(
	SELECT
		crm_bill_order_info.order_code AS code1,
		Min( crm_bill_order_info.account_month ) AS month1 
	FROM
		crm_bill_order_info 
	WHERE
		crm_bill_order_info.customer = "客户名称" 
	GROUP BY
		crm_bill_order_info.order_code 
	)
	INNER JOIN crm_bill_order_info ON ( code1 = crm_bill_order_info.order_code ) 
	AND ( month1 = crm_bill_order_info.account_month );

得到错误提示：

1248 - Every derived table must have its own alias

修改：需要在子查询后赋予 “as [name]：as order_first_date”

-- 查询订单首次出现的账期
SELECT
	order_first_date.code1,
	order_first_date.month1,
	crm_bill_order_info.server_start_date 
FROM
	(
	SELECT
		crm_bill_order_info.order_code AS code1,
		Min( crm_bill_order_info.account_month ) AS month1 
	FROM
		crm_bill_order_info 
	WHERE
		crm_bill_order_info.customer = "客户名称" 
	GROUP BY
		crm_bill_order_info.order_code 
	) AS order_first_date
	INNER JOIN crm_bill_order_info ON ( order_first_date.code1 = crm_bill_order_info.order_code ) 
	AND ( order_first_date.month1 = crm_bill_order_info.account_month );

当遇到错误才能记忆的更清晰，才能提高。
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