如何做一個搜索查詢

Question

我想知道怎麼做取決於@FirstName和@LastName（價值一WHERE語句中的IF聲明，如果它是null 這裏是我的代碼：

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

Answer 1

我以爲你是在尋找這樣的：

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

這樣，如果一個參數是空的where子句會忽略它
請ñ。注意它不會返回列爲空的任何行。

如果您的列可以爲空，並且您想要將它們爲空的行重新渲染，那麼您需要使用Bennjoe Mordeno的答案中的where子句。

Answer 2

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

如果該參數爲null，它沒有什麼需要做的，如果任何一個變量的值是空列

Answer 3

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