获取从查询返回的总 mysql 结果有限制：FOUND_ROWS 错误答案

【问题标题】：Getting total mysql results returned from query with a limit: FOUND_ROWS error获取从查询返回的总 mysql 结果有限制：FOUND_ROWS 错误
【发布时间】：2012-10-06 14:13:35
【问题描述】：

我有这个 mysql 查询：

SELECT Files.GUID, Files.Name, Files.Type, Files.Visibility, Files.CreationDate, Files.OwnerUser, Date, BackupsCount
FROM Files
  LEFT JOIN (
    SELECT FileGUID, Date, COUNT(*) AS BackupsCount
    FROM Versions
    GROUP BY FileGUID
  ) Versions ON Files.GUID = Versions.FileGUID
WHERE Files.ParentFolder = '96251A8B-B2A8-416B-92D7-3509E6A645C7'
ORDER BY Files.Type DESC, CreationDate ASC
LIMIT 0, 50

我想知道这个查询会返回多少条记录如果没有 LIMIT 指令，我用 Google 搜索发现需要添加 SELECT SQL_CALC_FOUND_ROWS 和 SELECT FOUND_ROWS();

我的问题是：我无法让它工作：

SELECT SQL_CALC_FOUND_ROWS * FROM (
SELECT Files.GUID, Files.Name, Files.Type, Files.Visibility, Files.CreationDate, Files.OwnerUser, Date, BackupsCount
FROM Files
  LEFT JOIN (
    SELECT FileGUID, Date, COUNT(*) AS BackupsCount
    FROM Versions
    GROUP BY FileGUID
  ) Versions ON Files.GUID = Versions.FileGUID
WHERE Files.ParentFolder = '96251A8B-B2A8-416B-92D7-3509E6A645C7'
ORDER BY Files.Type DESC, CreationDate ASC
LIMIT 0, 50)

-- Find total rows
SELECT FOUND_ROWS()

假设这是个好主意（我的意思是做一个查询而不是两个单独的查询），我怎样才能让 FOUND_ROWS() 处理这个查询？

【问题讨论】：

标签： mysql join left-join limit

【解决方案1】：

查询应该是这样的：

SELECT SQL_CALC_FOUND_ROWS Files.GUID, Files.Name, Files.Type, Files.Visibility, Files.CreationDate, Files.OwnerUser, Date, BackupsCount
FROM Files
  LEFT JOIN (
    SELECT FileGUID, Date, COUNT(*) AS BackupsCount
    FROM Versions
    GROUP BY FileGUID
  ) Versions ON Files.GUID = Versions.FileGUID
WHERE Files.ParentFolder = '96251A8B-B2A8-416B-92D7-3509E6A645C7'
ORDER BY Files.Type DESC, CreationDate ASC
LIMIT 0, 50

【讨论】：

谢谢，但查询仍然只返回行，而我需要行和总计数
您可以通过执行以下操作获得计数：SELECT FOUND_ROWS() 在第一个查询之后

【解决方案2】：

这个想法是正确的，第二个查询几乎是瞬时的。但是你必须在SELECT之后添加关键字，没有更多：

SELECT Files.GUID, Files.Name, Files.Type, ...

变成

SELECT SQL_CALC_FOUND_ROWS Files.GUID, Files.Name, Files.Type, ...

然后将填充找到的行数，您将能够恢复它。

如果您想运行单个 retrieval 查询，但您能够执行多个查询，那么您可以这样做（这是两个查询）：

SELECT COUNT(*) INTO @FOUNDROWS FROM ( YOUR_QUERY_WITHOUT_SELECT ) AS orig;

并通过在字段中添加 @FOUNDROWS as foundrows 来更改您的检索查询：

SELECT ...YOUR FIELDS..., @FOUNDROWS AS foundrows FROM...

最后，您可以将 JOIN 作为包含两个查询的单个查询运行：

SELECT ALL_YOUR_FIELDS, counter.FOUND_ROW_NUMBER FROM
( YOUR_QUERY_WITH_LIMIT ) AS limited
JOIN ( SELECT COUNT(*) AS FOUND_ROW_NUMBER FROM YOUR_QUERY ) AS counter;

【讨论】：

谢谢，但我仍然需要行和总计数。我的意思是添加SELECT SQL_CALC_FOUND_ROWS 在我运行时没有显示总数
不，不会的；它只存储计数，然后您必须在第二个查询中检索它。您可以在一个查询中完成，但这会花费您...我会尝试改进我的答案。

【解决方案3】：

A very simple example


 "SELECT SUM(final_cost) as final_cost,
SUM(call_discount) as discount_cost,
(SELECT COUNT(*) FROM call_records WHERE transaction_type ='call' AND account_id='$account_id' AND time_of_call>='$from' AND time_of_call<='$to' ) as calls,
(SELECT COUNT(*) FROM call_records WHERE transaction_type ='text' AND account_id='$account_id' AND time_of_call>='$from' AND time_of_call<='$to' ) as texts,
(SELECT COUNT(*) FROM call_records WHERE transaction_type ='appointment' AND account_id='$account_id' AND time_of_call>='$from' AND time_of_call<='$to' ) as appts
 FROM
 call_records
 WHERE account_id='$account_id'
 AND time_of_call>='$from'
 AND time_of_call<='$to' "

【讨论】：