也许我说这一切都错了，我是Linq的新手，但如果有人可以帮助我，我真的很感激。以下是我的代码。我正在尝试在标题和详细信息表中对信息进行总结。因此，我可以看到每个商家位置的总销售额和总访问次数（单个交易）。详细信息表将标题表中的1个事务分成多行，因此1个事务ID可以在详细信息表中多次出现。
var query2 = db.sales_transaction_header
.Join(db.sales_transaction_detail,
sth => sth.transaction_id,
std => std.transaction_id,
(sth, std) => new { TransHeader = sth, TransDetail = std })
.GroupBy(x => x.TransHeader.merchant_location_id)
.Select(g => new MerchantConsumerSalesDTO
{
TotalSales = g.Sum(x => x.TransDetail.transaction_amount),
MerchantId = g.FirstOrDefault().TransHeader.merchant_location_id,
TotalVisits = g.GroupBy(x => x.TransHeader.transaction_id).Select(g2 => g2.Count()),
})
.ToList();
TotalVisits给了我各种各样的问题！我最初尝试过
TotalVisits = g.Select(x => x.TransHeader.transaction_id).Distinct().Count()
但这给了我一个莫名其妙的错误：
'where子句'
中的未知列'Project3.merchant_location_id'
没有.Distinct（），它会正确返回Count（），除非是错误的数字！因为我只需要计算不同的值，但是使用Distinct（）它会给我一个错误！所以我尝试在子组上使用GroupBy。这甚至不允许我编译。我得到各种错误，例如“不能隐式地将Ienumerable转换为int”或“无法将匿名类型转换为int” - 我在我的智慧结束！我是完全走错了轨道还是这个小而简单的东西？
提前致谢！
修改 也许这有助于澄清我的意图。我的表格结构如下：
sales_transaction_header
transaction_id
merchant_location_id
card
transaction_date
sales_transaction_detail
transaction_detail_id
transaction_id
transaction_amount
seat_nbr
因此，基本上可以根据seat_nbr将单个事务分解为多个详细信息行。因此，如果我理解正确的话，第一个groupby应该只对商家ID进行分组，仍然为个别交易留下多行。我需要另一组来计算唯一的事务ID。正确的吗？
此外，我生成的查询如下：
SELECT `Project2`.`merchant_location_id`,
`Project2`.`c1`,
`Project2`.`merchant_location_id1`,
(SELECT Count(1) AS `A1`
FROM (SELECT DISTINCT `Extent7`.`transaction_id`
FROM `sales_transaction_header` AS `Extent7`
INNER JOIN `sales_transaction_detail` AS `Extent8`
ON `Extent7`.`transaction_id` =
`Extent8`.`transaction_id`
WHERE `Project2`.`merchant_location_id` =
`Extent7`.`merchant_location_id`) AS
`Distinct2`) AS `C2`
FROM (SELECT `Apply1`.`merchant_location_id`,
`Apply1`.`merchant_location_id`
AS `merchant_location_id1`,
(SELECT Sum(`Extent6`.`transaction_amount`) AS `A1`
FROM `sales_transaction_header` AS `Extent5`
INNER JOIN `sales_transaction_detail` AS `Extent6`
ON `Extent5`.`transaction_id` =
`Extent6`.`transaction_id`
WHERE `Apply1`.`merchant_location_id` =
`Extent5`.`merchant_location_id`) AS
`C1`
FROM (SELECT `Distinct1`.`merchant_location_id`,
(SELECT `Extent3`.`transaction_id`
FROM `sales_transaction_header` AS `Extent3`
INNER JOIN `sales_transaction_detail` AS
`Extent4`
ON `Extent3`.`transaction_id` =
`Extent4`.`transaction_id`
WHERE `Distinct1`.`merchant_location_id` =
`Extent3`.`merchant_location_id`
LIMIT 1) AS `transaction_id`,
(SELECT `Extent3`.`merchant_location_id`
FROM `sales_transaction_header` AS `Extent3`
INNER JOIN `sales_transaction_detail` AS
`Extent4`
ON `Extent3`.`transaction_id` =
`Extent4`.`transaction_id`
WHERE `Distinct1`.`merchant_location_id` =
`Extent3`.`merchant_location_id`
LIMIT 1) AS `MERCHANT_LOCATION_ID1`,
(SELECT `Extent3`.`transaction_date`
FROM `sales_transaction_header` AS `Extent3`
INNER JOIN `sales_transaction_detail` AS
`Extent4`
ON `Extent3`.`transaction_id` =
`Extent4`.`transaction_id`
WHERE `Distinct1`.`merchant_location_id` =
`Extent3`.`merchant_location_id`
LIMIT 1) AS `transaction_date`,
(SELECT `Extent3`.`post_date`
FROM `sales_transaction_header` AS `Extent3`
INNER JOIN `sales_transaction_detail` AS
`Extent4`
ON `Extent3`.`transaction_id` =
`Extent4`.`transaction_id`
WHERE `Distinct1`.`merchant_location_id` =
`Extent3`.`merchant_location_id`
LIMIT 1) AS `post_date`,
(SELECT `Extent3`.`card_token`
FROM `sales_transaction_header` AS `Extent3`
INNER JOIN `sales_transaction_detail` AS
`Extent4`
ON `Extent3`.`transaction_id` =
`Extent4`.`transaction_id`
WHERE `Distinct1`.`merchant_location_id` =
`Extent3`.`merchant_location_id`
LIMIT 1) AS `card_token`,
(SELECT `Extent3`.`transaction_type`
FROM `sales_transaction_header` AS `Extent3`
INNER JOIN `sales_transaction_detail` AS
`Extent4`
ON `Extent3`.`transaction_id` =
`Extent4`.`transaction_id`
WHERE `Distinct1`.`merchant_location_id` =
`Extent3`.`merchant_location_id`
LIMIT 1) AS `transaction_type`,
(SELECT `Extent3`.`processed`
FROM `sales_transaction_header` AS `Extent3`
INNER JOIN `sales_transaction_detail` AS
`Extent4`
ON `Extent3`.`transaction_id` =
`Extent4`.`transaction_id`
WHERE `Distinct1`.`merchant_location_id` =
`Extent3`.`merchant_location_id`
LIMIT 1) AS `processed`,
(SELECT `Extent3`.`partner_transaction_id`
FROM `sales_transaction_header` AS `Extent3`
INNER JOIN `sales_transaction_detail` AS
`Extent4`
ON `Extent3`.`transaction_id` =
`Extent4`.`transaction_id`
WHERE `Distinct1`.`merchant_location_id` =
`Extent3`.`merchant_location_id`
LIMIT 1) AS `partner_transaction_id`,
(SELECT `Extent4`.`transaction_detail_id`
FROM `sales_transaction_header` AS `Extent3`
INNER JOIN `sales_transaction_detail` AS
`Extent4`
ON `Extent3`.`transaction_id` =
`Extent4`.`transaction_id`
WHERE `Distinct1`.`merchant_location_id` =
`Extent3`.`merchant_location_id`
LIMIT 1) AS `transaction_detail_id`,
(SELECT `Extent4`.`transaction_id` AS `TRANSACTION_ID1`
FROM `sales_transaction_header` AS `Extent3`
INNER JOIN `sales_transaction_detail` AS
`Extent4`
ON `Extent3`.`transaction_id` =
`Extent4`.`transaction_id`
WHERE `Distinct1`.`merchant_location_id` =
`Extent3`.`merchant_location_id`
LIMIT 1) AS `TRANSACTION_ID1`,
(SELECT `Extent4`.`transaction_amount`
FROM `sales_transaction_header` AS `Extent3`
INNER JOIN `sales_transaction_detail` AS
`Extent4`
ON `Extent3`.`transaction_id` =
`Extent4`.`transaction_id`
WHERE `Distinct1`.`merchant_location_id` =
`Extent3`.`merchant_location_id`
LIMIT 1) AS `transaction_amount`,
(SELECT `Extent4`.`charity_location_id`
FROM `sales_transaction_header` AS `Extent3`
INNER JOIN `sales_transaction_detail` AS
`Extent4`
ON `Extent3`.`transaction_id` =
`Extent4`.`transaction_id`
WHERE `Distinct1`.`merchant_location_id` =
`Extent3`.`merchant_location_id`
LIMIT 1) AS `charity_location_id`,
(SELECT `Extent4`.`event_type_id`
FROM `sales_transaction_header` AS `Extent3`
INNER JOIN `sales_transaction_detail` AS
`Extent4`
ON `Extent3`.`transaction_id` =
`Extent4`.`transaction_id`
WHERE `Distinct1`.`merchant_location_id` =
`Extent3`.`merchant_location_id`
LIMIT 1) AS `event_type_id`
FROM (SELECT DISTINCT `Extent1`.`merchant_location_id`
FROM `sales_transaction_header` AS `Extent1`
INNER JOIN `sales_transaction_detail` AS
`Extent2`
ON `Extent1`.`transaction_id` =
`Extent2`.`transaction_id`) AS
`Distinct1`) AS `Apply1`) AS `Project2`
更新
最终，我选择了：
var query = db.sales_transaction_header
.Join(db.sales_transaction_detail,
sth => sth.transaction_id,
std => std.transaction_id,
(sth, std) => new { TransHeader = sth, TransDetail = std })
.GroupBy(x => x.TransHeader.merchant_location_id)
.ToList()
.Select(g => new MerchantConsumerSalesDTO
{
TotalSales = g.Sum(x => x.TransDetail.transaction_amount),
MerchantId = g.Key,
TotalConsumerVisits = g.GroupBy(x => x.TransHeader.transaction_id).Count(),
});
这是由于我正在使用的MySql数据库的限制 - 它在MSSQL中工作很好，显然无需使用ToList（），但至少它现在正在工作！非常感谢，ROB！
答案 0 :(得分：0)
在chat进行讨论后，结果表明该行为是由于MySql连接器中的错误造成的。
以下代码通过评估内存中的组来解决此错误：
var query = db.sales_transaction_header
.Join(db.sales_transaction_detail,
sth => sth.transaction_id,
std => std.transaction_id,
(sth, std) => new {TransHeader = sth, TransDetail = std})
.GroupBy(x => x.TransHeader.merchant_location_id)
.ToList()
.Select(g => new MerchantConsumerSalesDTO
{
TotalSales = g.Sum(x => x.TransDetail.transaction_amount),
MerchantId = g.Key,
TotalConsumerVisits = g.GroupBy(x => x.TransHeader.transaction_id).Count(),
});
这是因为它生成以下代码：
SELECT `GroupBy1`.`k1` AS `merchant_location_id`,
`GroupBy1`.`a1` AS `C1`,
(SELECT Count(1) AS `A1`
FROM (SELECT DISTINCT `Extent3`.`transaction_id`
FROM `sales_transaction_header` AS `Extent3`
INNER JOIN `sales_transaction_detail` AS `Extent4`
ON `Extent3`.`transaction_id` =
`Extent4`.`transaction_id`
WHERE `GroupBy1`.`k1` = `Extent3`.`merchant_location_id`) AS
`Distinct1`) AS `C2`
FROM (SELECT `Extent1`.`merchant_location_id` AS `K1`,
Sum(`Extent2`.`transaction_amount`) AS `A1`
FROM `sales_transaction_header` AS `Extent1`
INNER JOIN `sales_transaction_detail` AS `Extent2`
ON `Extent1`.`transaction_id` =
`Extent2`.`transaction_id`
GROUP BY `Extent1`.`merchant_location_id`) AS `GroupBy1`
在MySql中，内部选择不能引用外部结果，所以这一行：
`GroupBy1`.`k1` = `Extent3`.`merchant_location_id`
失败，因为GroupBy1超出了选择范围。
修复是在组后添加ToList()，以便最终选择（和总结）在内存中完成