Question

我有这样的查询：

SELECT 
       generatedTime AS generatedTime,
       tempTable AS tempTable,
       CASE
           WHEN ((generatedTime < maxPelamarmhsdoktor) or (generatedTime < maxAkdmstmayor)
                    or (generatedTime < maxIpbmstdepartemen) or (generatedTime < maxIpbmstfakultas)
                        or (generatedTime < maxIpbrefjeniskelamin) or (generatedTime < maxJenisinstansi)
                            or (generatedTime < maxJenisinstitusi)) THEN
               'Yes'
           ELSE
               'No'
       END AS NeedsToUpdateorNot
FROM generatedtime
JOIN ( SELECT 
              MAX( last_update ) AS maxPelamarmhsdoktor
       FROM pelamarmhsdoktor

     ) AS maxPelamarmhsdoktorFinder
JOIN ( SELECT 
              MAX( last_update ) AS maxAkdmstmayor
       FROM akdmst_mayor

     ) AS maxAkdmstmayorFinder
JOIN ( SELECT 
              MAX( last_update ) AS maxIpbmstdepartemen
       FROM ipbmst_departemen

     ) AS maxIpbmstdepartemenFinder
JOIN ( SELECT 
              MAX( last_update ) AS maxIpbmstfakultas
       FROM ipbmst_fakultas

     ) AS maxIpbmstfakultasFinder
JOIN ( SELECT 
              MAX( last_update ) AS maxIpbrefjeniskelamin
       FROM ipbref_jeniskelamin

     ) AS maxIpbrefjeniskelaminFinder
JOIN ( SELECT 
              MAX( last_update ) AS maxJenisinstansi
       FROM jenisinstansi

     ) AS maxJenisinstansiFinder
JOIN ( SELECT 
              MAX( last_update ) AS maxJenisinstitusi
       FROM jenisinstitusi

     ) AS maxJenisinstitusiFinder

然后我想让该查询成为一个视图表。所以我添加了

CREATE ALGORITHM=UNDEFINED DEFINER=`root`@`localhost` SQL SECURITY DEFINER VIEW `updateforpelamarmagisterrinci`  AS

一开始。

但是当我尝试创建视图时，出现错误，错误消息就像这样

#1349 - View's SELECT contains a subquery in the FROM clause

我可以做些什么来解决这个问题？提前致谢

Answer 1

由于您使用的是MariaDB 10.1，因此您可能需要考虑升级到MariaDB 10.2。在视图was removed in 10.2.1中使用子查询的限制。截至目前（2017年5月13日），最新的10.2版本为10.2.5-rc。

下一个10.2.6将是GA（a.k.a.稳定版），即将推出。同时，您将有时间测试10.2功能是否适合您，这就是RC的用途。

注意：如果您决定尝试升级，强烈建议您在执行此操作之前创建数据库的备份。如果您因任何原因不喜欢该版本并希望降级，使用备份可能会省力。

Answer 2

根据MySQL的documentation，您在创建FROM时无法在VIEW子句中进行子查询，因此会出错。但是，在您的情况下，您可以更改查询并尝试在SELECT子句中选择这些值，例如

SELECT 
       (SELECT MAX( last_update ) FROM pelamarmhsdoktor) AS maxPelamarmhsdoktorFinder,
       (SELECT MAX( last_update ) FROM akdmst_mayor) AS maxAkdmstmayorFinder,
       (SELECT MAX( last_update ) FROM ipbmst_departemen) AS maxIpbmstdepartemenFinder,
       (SELECT MAX( last_update ) FROM ipbmst_fakultas) AS maxIpbmstfakultasFinder,
       (SELECT MAX( last_update ) FROM ipbref_jeniskelamin) AS maxJeniskelamin,
       generatedTime AS generatedTime,
       tempTable AS tempTable,
       CASE
           WHEN ((generatedTime < maxPelamarmhsdoktor) or (generatedTime < maxAkdmstmayor)
                    or (generatedTime < maxIpbmstdepartemen) or (generatedTime < maxIpbmstfakultas)
                        or (generatedTime < maxIpbrefjeniskelamin) or (generatedTime < maxJenisinstansi)
                            or (generatedTime < maxJenisinstitusi)) THEN
               'Yes'
           ELSE
               'No'
       END AS NeedsToUpdateorNot
FROM generatedtime;

Answer 3

这是一个解决方案，结构合理，但有些工作：

为需要时间列的每个表创建一个视图。您在此视图中所做的只是选择MAX(last_update)。
创建一个视图，其中UNION在步骤1中创建的所有视图，然后再次选择MAX(last_update)，为简单起见，我调用视图vAll。
< / LI>

现在您可以轻松创建您想要的视图：

SELECT
   generatedTime AS generatedTime,
   tempTable AS tempTable,
   CASE WHEN generated_time < last_update THEN 'Yes' ELSE 'No' END AS NeedsToUpdateorNot
FROM generatedtime, vAll;

或者尝试在select子句中执行所有操作：

SELECT
   generatedTime AS generatedTime,
   tempTable AS tempTable,
   CASE WHEN generated_time < (
      SELECT MAX(last_update) AS last_update FROM (
          (SELECT MAX(last_update) AS last_update FROM a) UNION
          (SELECT MAX(last_update) AS last_update FROM b) UNION
          (SELECT MAX(last_update) AS last_update FROM c) UNION
          ...
      )
   ) THEN 'Yes' ELSE 'No' END AS NeedsToUpdateorNot
FROM generatedtime;

Answer 4

将您的子查询移至视图：

CREATE VIEW v_max_pelamarmhsdoktor AS 
    SELECT MAX( last_update ) AS maxPelamarmhsdoktor FROM pelamarmhsdoktor
...

...

您的查询变为：

SELECT 
       generatedTime AS generatedTime,
       tempTable AS tempTable,
       CASE
           WHEN ((generatedTime < maxPelamarmhsdoktor) or (generatedTime < maxAkdmstmayor)
                    or (generatedTime < maxIpbmstdepartemen) or (generatedTime < maxIpbmstfakultas)
                        or (generatedTime < maxIpbrefjeniskelamin) or (generatedTime < maxJenisinstansi)
                            or (generatedTime < maxJenisinstitusi)) THEN
               'Yes'
           ELSE
               'No'
       END AS NeedsToUpdateorNot
FROM generatedtime
JOIN v_max_pelamarmhsdoktor AS maxPelamarmhsdoktorFinder
...

...

为什么我不能在SQL中创建视图表？

4 个答案: