調用本地函數'ISNULL'時的錯誤參數計數

Question

我有一個查詢，我試圖從MS SQL Server 2008轉換爲MySQL。它在MSSQL上運行正常， 我得到錯誤 「Incorrect parameter count in the call to native function 'ISNULL'」。

我該如何解決這個問題？

SELECT DISTINCT 
    dbo.`@EIM_PROCESS_DATA`.U_Tax_year, 
    dbo.`@EIM_PROCESS_DATA`.U_Employee_ID, 
    CASE 
     WHEN dbo.`@EIM_PROCESS_DATA`.U_PD_code = 'SYS033' THEN SUM(dbo.`@EIM_PROCESS_DATA`.U_Amount) 
    END AS PAYE, 
    CASE 
     WHEN dbo.`@EIM_PROCESS_DATA`.U_PD_code = 'SYS014' THEN SUM(dbo.`@EIM_PROCESS_DATA`.U_Amount) 
    END AS TOTALTAXABLE, 
    dbo.OADM.CompnyName, 
    dbo.OADM.CompnyAddr, 
    dbo.OADM.TaxIdNum, 
    dbo.OHEM.lastName + ', ' + ISNULL(dbo.OHEM.middleName, '') + '' + ISNULL(dbo.OHEM.firstName, '') AS EmployeeName 
FROM 
    dbo.`@EIM_PROCESS_DATA` 
     INNER JOIN 
    dbo.OHEM ON dbo.`@EIM_PROCESS_DATA`.U_Employee_ID = dbo.OHEM.empID 
     CROSS JOIN 
    dbo.OADM 
GROUP BY dbo.`@EIM_PROCESS_DATA`.U_Tax_year , dbo.`@EIM_PROCESS_DATA`.U_Employee_ID , dbo.OADM.CompnyName , dbo.OADM.CompnyAddr , dbo.OADM.TaxIdNum , dbo.OHEM.lastName , dbo.OHEM.firstName , dbo.OHEM.middleName , dbo.`@EIM_PROCESS_DATA`.U_PD_code 

的MySQL

SELECT DISTINCT 
    processdata.taxYear, processdata.empID, 
    CASE WHEN processdata.edCode = 'SYS033' THEN SUM (processdata.amount) END AS PAYE, 
    CASE WHEN processdata.edCode = 'SYS014' THEN SUM (processdata.amount) END AS TOTALTAXABLE, 
    company.companyName, company.streetAddress, company.companyPIN, employeemaster.lastName + ', ' + IFNULL(employeemaster.middleName, '') 
    + ' ' + IFNULL(employeemaster.firstName, '') AS EmployeeName 
FROM   
    processdata INNER JOIN 
    employeemaster ON processdata.empID = employeemaster.empID 
    CROSS JOIN company 
    GROUP BY processdata.taxYear, processdata.empID, company.companyName, company.streetAddress, company.companyPIN, 
    employeemaster.lastName, employeemaster.firstName, employeemaster.middleName, processdata.edCode 

Answer 1

MySQL的等效的ISNULL的是IFNULL

如果expr1不是NULL，IFNULL（）返回表達式1;否則返回 expr2。

也許還看SQL NULL Functions

The ISNULL from MySQL is used to check if a value is null

如果expr是NULL，ISNULL（）返回1，否則返回0

Answer 2

我建議你切換到ANSI標準功能coalesce()：

(dbo.OHEM.lastName + ', ' + coalesce(dbo.OHEM.middleName, '') + '' + coalesce(dbo.OHEM.firstName, '') 
) AS EmployeeName 

您還可以通過包含表別名來使您的查詢更易於閱讀。

編輯：

作爲一個說明，我似乎已經錯過了轉換的方向。 MySQL查詢將使用concat()：

CONCAT(OHEM.lastName, ', ', coalesce(OHEM.middleName, ''), 
     coalesce(concat(' ', OHEM.firstName), '') 
    ) AS EmployeeName