如何在SQL Server中使用where子句使用if else

Question

CREATE PROCEDURE findlist @comedianname1 nvarchar(30),@comedianname2 nvarchar(30)
AS
SELECT comedian 
FROM Comedian
if @comedianname2!=null
begin
WHERE comedian! = @comedianname1 and comedian! = @comedianname2
end
else
begin
WHERE comedian! = @comedianname1
end
GO

我收到此錯誤：消息156，級別15，狀態1，過程查找列表，第7行關鍵字“ WHERE”附近的語法不正確。

Answer 1

您不能在選擇中使用IF 。 您可以在這種情況下執行以下操作：

SELECT comedian 
FROM Comedian
WHERE
    comedian! = @comedianname1 AND
    comedian! = ISNULL(@comedianname2, comedian!)

它有什么作用？ 如果比較comedian! 到@comedianname1 ，如果@comedianname2不為null，它將比較comedian! 到@comedianname2 。 否則它比較comedian! 來comedian! ，這總是true 。

Answer 2

您需要使用以下查詢

SELECT comedian 
FROM Comedian
WHERE comedian! = @comedianname1 and (comedian! = @comedianname2 OR @comedianname2 IS NULL)

Answer 3

嘗試這個

CREATE PROCEDURE findlist @comedianname1 nvarchar(30),@comedianname2 nvarchar(30)
AS
  SELECT comedian 
  FROM Comedian
  WHERE (comedian! = @comedianname1 and comedian! = @comedianname2) OR (comedian! = @comedianname1)
GO