Question

数据库包含4个表格-费用，月份，客户，发票。

表格-month（费用期）

（包含1月至12月的所有月份，此处仅两个月，以简化问题）

id  |   ttl |   year
====================
1   |   Jan |   1
2   |   Feb |   1

表格-fee（费用名称）

id  |   ttl     |   year
========================
1   |   Annual  |   1
2   |   Monthly |   1
3   |   Extra   |   1

表格-customer（客户名称）

id  |   ttl     |   year
========================
1   |   Rahul   |   1

表格-invoice（发票列表）

id  |   cid |   fid |   mid
===========================
1   |   1   |   1   |   1
2   |   1   |   2   |   1

在12个月内，必须每月每个月支付月费和额外费用。

但是年费是一次支付，在不固定的月份支付，可以在1月或12月或该月之间的任何月份支付。

现在，我的要求是显示尚未准备好发票的相关月份的每笔费用（不在发票表中的每月费用名称），只需列出未付款的月份费用列表。所以我将LEFT JOIN与NULL

一起使用

SELECT
    customer.id AS cid,
    month.id AS mid,
    fee.id AS fid,
    month.ttl AS mth,
    fee.ttl AS fee,
FROM
    fee
LEFT JOIN
    month ON month.year = fee.year
LEFT JOIN
    customer ON customer.year = fee.year
LEFT JOIN
    invoice ON invoice.mid = month.id AND invoice.fid = fee.id
WHERE
    customer.id=1 AND invoice.fid IS NULL

结果是-

cid |   mid |   fid |   mth |   fee 
=======================================
1   |   1   |   3   |   Jan |   Extra
1   |   2   |   1   |   Feb |   Annual  
1   |   2   |   2   |   Feb |   Monthly 
1   |   2   |   3   |   Feb |   Extra

但是，我想要的是-如上所述，年费仅支付一次，因此，如果是“年鉴”发票，则应排除此费用（如果不包括在内）以得到以下结果

cid |   mid |   fid |   mth |   fee 
=======================================
1   |   1   |   3   |   Jan |   Extra
1   |   2   |   2   |   Feb |   Monthly 
1   |   2   |   3   |   Feb |   Extra

因为年费已在1月支付。

所以我要编辑条件

WHERE
    customer.id=1 
AND 
    invoice.fid IS NULL 
AND 
    NOT EXISTS (select invoice.fid from invoice where invoice.fid = 1 AND invoice.cid=customer.id)

但是MySQL返回了一个空结果集

Answer 1

您缺少客户invoice在customer和id表之间的JOIN条件。
由于在month和fee表之间进行联接，因此对于fee.ttl = 'Annual'而言，您将获得多行。
一种方法是将其分为两个不同的SELECT查询，并使用UNION ALL。首选查询考虑fee.ttl != 'Annual'。第二选择仅考虑fee.ttl = 'Annual'的情况。在第二个Select查询中，我们不与month表联接，因此避免了“ Annual”的多个行。
请注意，我在ttl字段中匹配了“ Annual”，而不是fid。似乎由于年份不同，“年度”将有多个fid值。因此，检查fid = 1仅用于year = 1的目的。
还请注意，由于您的联接表排序，我已将您的某些Left联接更改为Inner联接。

尝试以下操作：

(SELECT
    customer.id AS cid,
    month.id AS mid,
    fee.id AS fid,
    month.ttl AS mth,
    fee.ttl AS fee 
FROM
    fee
INNER JOIN
    month ON month.year = fee.year
INNER JOIN
    customer ON customer.year = fee.year
LEFT JOIN
    invoice ON invoice.mid = month.id AND 
               invoice.fid = fee.id AND 
               invoice.cid = customer.id 
WHERE
    customer.id = 1 AND 
    fee.ttl != 'Annual' AND 
    invoice.fid IS NULL
)

UNION ALL 

(SELECT
    customer.id AS cid,
    '' AS mid,
    fee.id AS fid,
    '' AS mth,
    fee.ttl AS fee 
FROM
    fee 
INNER JOIN
    customer ON customer.year = fee.year
LEFT JOIN
    invoice ON invoice.fid = fee.id AND 
               invoice.cid = customer.id 
WHERE
    customer.id = 1 AND 
    fee.ttl = 'Annual' AND 
    invoice.fid IS NULL
)

不存在，返回空结果集

1 个答案: