Question

我想知道如何在IF语句中执行WHERE语句，具体取决于@FirstName和@LastName的值（如果它是null { {1}} 这是我的代码：

SELECT tblCustomers.CustomerFirstName, tblCustomers.CustomerLastName FROm tblCustomers
    where CustomerFirstName = @FirstName and CustomerLastName = @LastName

Answer 1

我认为你正在寻找这个：

SELECT tblCustomers.CustomerFirstName, tblCustomers.CustomerLastName 
FROM tblCustomers
WHERE CustomerFirstName = COALESCE(@FirstName, CustomerFirstName)
AND CustomerLastName = COALESCE(@LastName, CustomerLastName)

这样，如果参数为null，则where子句将忽略它请注意，它不会返回列为空的任何行。

如果您的列可以为空并且您想要将它们为null的行重新归档，则需要使用Bennjoe Mordeno的答案中建议的where子句。

Answer 2

Use CASE Statement in WHERE Clause :

SELECT tblCustomers.CustomerFirstName, tblCustomers.CustomerLastName 
FROM tblCustomers
WHERE CustomerFirstName = CASE 
      WHEN ISNULL(@FirstName,'') <> '' THEN @FirstName ELSE CustomerFirstName END AND CustomerLastName = WHEN ISNULL(@LastName,'') <> '' THEN @LastName ELSE CustomerLastName END

Answer 3

SELECT tblCustomers.CustomerFirstName, tblCustomers.CustomerLastName FROm tblCustomers
where (CustomerFirstName = @FirstName OR @FirstName IS NULL) and (CustomerLastName = @LastName OR @LastName IS NULL)

如果参数为null，则不必匹配列

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