Question

我有两个具有不同字段的表：

SELECT url, title, description, impact, solution, severitylevel, category
FROM admin_cyber.sss3wn
WHERE severitylevel = "5" 
AND client = "user1" 
UNION
SELECT name, risk, host, protocol, port, pluginoutput, description, solution
FROM admin_cyber.sss1wn
WHERE risk = "Critical" AND client = "myuser1"
AND datescanned IN (SELECT max(datescanned) FROM admin_cyber.sss1wn

常见字段是：客户端，已扫描日期

我只想查询两个表并仅检索最新日期的数据。

两个表是否都需要具有确切的字段才能出现在UNION中？

问题2：如果我知道sss3wn中的“ url”字段和sss1wn中的“ host”字段具有相同的含义，我可以将它们以相同的名称分组吗？

谢谢！娜塔莉（Nathalie）

Answer 1

对于UNION，表是否具有相同的字段无关紧要，因为两个SELECT语句上所选列的数量都匹配。

因此，两个SELECT都必须选择相同数量的列，并且每个SELECT中匹配的列都应具有相同的dataType（如果可以的话，您可以CAST强制使用相同的dataType）。

示例：

SELECT 
  url AS Field1, 
  title AS Field2, 
  description AS Field3, 
  impact AS Field4, 
  solution AS Field5, 
  severitylevel AS Field6, 
  category AS Field7,
  "-" AS Field8
FROM admin_cyber.sss3wn
WHERE severitylevel = "5" 
  AND client = "user1" 
UNION
SELECT 
  name AS Field1, 
  risk AS Field2, 
  host AS Field3, 
  protocol AS Field4, 
  CAST(port AS NVarChar) AS Field5, 
  pluginoutput AS Field6, 
  description AS Field7, 
  solution AS Field8
FROM admin_cyber.sss1wn
WHERE risk = "Critical" AND client = "myuser1"
AND datescanned IN (SELECT max(datescanned) FROM admin_cyber.sss1wn);

我假设所有匹配的字段都具有相同的dataType（除了solution：NvarChar和port：integer用作示例，您可以如何投射某些内容）。在第8个字段中，在第一个语句上选择了一个常量，以强制在SELECT语句之间进行相同数量的选择。

执行此UNION可能没有任何意义（在我看来，匹配的字段与其含义没有任何关系），但这就是UNION的样子。

编辑：如果实际上来自两个SELECT的数据确实不同（含义），但仍需要将它们作为单个结果集列出，则可以执行以下操作：

SELECT 
  "INCIDENT" AS RowType,
  url AS Url_or_Name, 
  title AS Title_or_Risk, 
  description AS Desc_or_Host, 
  impact AS Impct_or_Prot, 
  solution AS Sol_or_Port, 
  severitylevel AS Lvl_or_Output, 
  category AS Cat_or_Desc,
  "-" AS Field8
FROM admin_cyber.sss3wn
WHERE severitylevel = "5" 
  AND client = "user1" 
UNION
SELECT 
  "CONNECTION" AS RowType,
  name AS Url_or_Name, 
  risk AS Title_or_Risk, 
  host AS Desc_or_Host, 
  protocol AS Impct_or_Prot, 
  CAST(port AS NVarChar) AS Sol_or_Port, 
  pluginoutput AS Lvl_or_Output, 
  description AS Cat_or_Desc, 
  solution AS Field8
FROM admin_cyber.sss1wn
WHERE risk = "Critical" AND client = "myuser1"
AND datescanned IN (SELECT max(datescanned) FROM admin_cyber.sss1wn);

或者您可能会发现，最好对选定的列进行重新排序，以使其与联合的结果列上的含义更好地匹配。

MySQL查询具有不同字段的两个表

1 个答案: