Question

我想仅从我的用户表中引用第一个结果，但我收到以下错误

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '1 CONCAT_WS(' ',employeeFirstName,employeeLastName) AS courseAdded FROM vwt_user' at line 6

我的SQL如下

CREATE OR REPLACE VIEW vwt_courses AS
SELECT tw_tblcourse.*, tw_tblprovider.providerName, CONCAT_WS(' ',vwt_userse.employeeFirstName,vwt_userse.employeeLastName) AS courseEditor, tw_tblprovider.providerAdd1, tw_tblprovider.providerAdd2, u_tbltowns.townName AS providerTown, tw_tblprovider.providerPostCode
FROM tw_tblcourse
JOIN tw_tblprovider ON tw_tblprovider.providerID = tw_tblcourse.courseProviderID
LEFT JOIN u_tbltowns ON u_tbltowns.townID = tw_tblprovider.providerTownID
JOIN vwt_users AS vwt_usersa ON vwt_usersa.userID = (SELECT TOP 1 CONCAT_WS(' ',employeeFirstName,employeeLastName) AS courseAdded FROM vwt_users WHERE userID=tw_tblcourse.courseAddedID)
LEFT JOIN vwt_users AS vwt_userse ON vwt_userse.userID = tw_tblcourse.courseEditedID

我一直在尝试按SQL Server: How to Join to first row的答案，但它不起作用，否则我做错了：）

我也尝试过： 不适用于MySQL，因此无法正常工作

CREATE OR REPLACE VIEW vwt_courses AS
SELECT tw_tblcourse.*, tw_tblprovider.providerName, CONCAT_WS(' ',vwt_usersa.employeeFirstName,vwt_usersa.employeeLastName) AS courseAdded, CONCAT_WS(' ',vwt_userse.employeeFirstName,vwt_userse.employeeLastName) AS courseEditor, tw_tblprovider.providerAdd1, tw_tblprovider.providerAdd2, u_tbltowns.townName AS providerTown, tw_tblprovider.providerPostCode
FROM tw_tblcourse
JOIN tw_tblprovider ON tw_tblprovider.providerID = tw_tblcourse.courseProviderID
LEFT JOIN u_tbltowns ON u_tbltowns.townID = tw_tblprovider.providerTownID
CROSS APPLY (SELECT  TOP 1 vwt_users.employeeFirstName, vwt_users.employeeLastName FROM vwt_users WHERE vwt_users.userID = tw_tblcourse.courseAddedID) vwt_usersa
LEFT JOIN vwt_users AS vwt_userse ON vwt_userse.userID = tw_tblcourse.courseEditedID

尝试3： 这个被接受但由于某种原因没有限制

CREATE OR REPLACE VIEW vwt_courses AS
SELECT tw_tblcourse.*, tw_tblprovider.providerName, CONCAT_WS(' ',vwt_usersa.employeeFirstName,vwt_usersa.employeeLastName) AS courseAdded, CONCAT_WS(' ',vwt_userse.employeeFirstName,vwt_userse.employeeLastName) AS courseEditor, tw_tblprovider.providerAdd1, tw_tblprovider.providerAdd2, u_tbltowns.townName AS providerTown, tw_tblprovider.providerPostCode
FROM tw_tblcourse
JOIN tw_tblprovider ON tw_tblprovider.providerID = tw_tblcourse.courseProviderID
LEFT JOIN u_tbltowns ON u_tbltowns.townID = tw_tblprovider.providerTownID
JOIN vwt_users AS vwt_usersa ON vwt_usersa.userID = (SELECT userID FROM vwt_users WHERE userID = tw_tblcourse.courseAddedID LIMIT 1)
LEFT JOIN vwt_users AS vwt_userse ON vwt_userse.userID = (SELECT userID FROM vwt_users WHERE userID = tw_tblcourse.courseEditedID LIMIT 1)

vwt_users示例：

╔════╦═══════╦══════╦══════╦══════╗
║ ID ║ FIRST ║ LAST ║ COMP ║ LIVE ║
╠════╬═══════╬══════╣══════╣══════╣
║  1 ║ JOHN  ║  DOE ║  1   ║  1   ║
║  1 ║ JOHN  ║  DOE ║  2   ║  1   ║
╚════╩═══════╩══════╩══════╩══════╝

实际字段包括用户ID，用户名，员工ID，名字，姓氏，电子邮件，用户级别，公司ID，公司名称，用户活动。其中，只有员工（ID，名字和姓氏）和公司（ID和姓名）详细信息发生变化

Answer 1

concat_ws()不是SQL Server函数。这是一个MySQL功能。你可以做你想做的事：

ON vwt_usersa.userID = (SELECT TOP 1 employeeFirstName + ' ' + employeeLastName AS courseAdded
                        FROM vwt_users
                        WHERE userID = tw_tblcourse.courseAddedID)

这可能无法正确处理NULLs。如果这很重要，您需要更多逻辑：

ON vwt_usersa.userID = (SELECT TOP 1 (case when employeeFirstName is NULl then employeeLastName
                                           when employeeLastName is NULL then emplyeeFirstName
                                           else employeeFirstName + ' ' + employeeLastName
                                      end) AS courseAdded
                        FROM vwt_users
                        WHERE userID = tw_tblcourse.courseAddedID)

Answer 2

TOP在MySQL中不可用，您需要使用LIMIT

 SELECT  vwt_users.employeeFirstName, vwt_users.employeeLastName FROM vwt_users WHERE vwt_users.userID = tw_tblcourse.courseAddedID
 order by
 vwt_users.employeeFirstName,     vwt_users.employeeLastName
 Limit 1

当您加入vwt_users时，其中多次具有相同的用户ID，结果将相同，相关子查询为您提供1行限制，但这是来自vwt_users的每个用户ID（此处为重复项）。

一种方法是使用类似于您的尝试2的交叉连接，并使用vwt_users删除连接

SELECT tw_tblcourse.*,
       tw_tblprovider.providerName, 
       CONCAT_WS(' ',vwt_usersa.employeeFirstName,vwt_usersa.employeeLastName) AS courseAdded,   
       CONCAT_WS(' ',vwt_userse.employeeFirstName,vwt_userse.employeeLastName) AS courseEditor 
       tw_tblprovider.providerAdd1, tw_tblprovider.providerAdd2, u_tbltowns.townName AS providerTown,  
       tw_tblprovider.providerPostCode
FROM tw_tblcourse
JOIN tw_tblprovider 
ON tw_tblprovider.providerID = tw_tblcourse.courseProviderID
LEFT JOIN u_tbltowns 
ON u_tbltowns.townID = tw_tblprovider.providerTownID
CROSS JOIN (SELECT vwt_users.employeeFirstName, vwt_users.employeeLastName FROM vwt_users WHERE userID = tw_tblcourse.courseAddedID LIMIT 1) vwt_usersa
CROSS JOIN (SELECT vwt_users.employeeFirstName, vwt_users.employeeLastName  FROM vwt_users WHERE userID = tw_tblcourse.courseEditedID LIMIT 1) vwt_userse

SQL JOIN与CONCAT_WS的第一行

2 个答案: