Question

我的表格创建如下：

CREATE TABLE StackFunctionID
(
    m_FunctionID int PRIMARY KEY IDENTITY,
    m_GroupID int DEFAULT 0 NOT NULL,
    m_Function varchar(256) UNIQUE NOT NULL,
);

GO
CREATE TRIGGER INSERT_MakeGroupID ON StackFunctionID AFTER INSERT AS
BEGIN
    SET NOCOUNT ON;

    UPDATE StackFunctionID
    SET StackFunctionID.m_GroupID = INSERTED.m_FunctionID
    FROM StackFunctionID
    INNER JOIN INSERTED ON (StackFunctionID.m_FunctionID = INSERTED.m_FunctionID)
END;

现在我正在尝试编写一个

的Sql Server 2008查询

如果m_Function不存在，请创建它，然后返回m_FunctionID，m_GroupID
如果m_Function存在，请返回m_FunctionID，m_GroupID
原子地执行

经过多次尝试，这是过去几年的成效：

DECLARE @Results TABLE(m_FunctionID INT, m_GroupID INT);  -- trash use
DECLARE @dummy1 int;                                      -- trash use
MERGE INTO StackFunctionID WITH(HOLDLOCK) AS Target       -- WITH(HOLDLOCK) for thread safety
USING (VALUES(null)) AS dummy2(dummy3)                    -- syntax requires USING
ON Target.m_Function = @m_Function
WHEN MATCHED THEN
    UPDATE SET @dummy1 = 0                                -- syntax requires something in 'WHEN MATCHED', which is needed for OUTPUT
WHEN NOT MATCHED THEN
    INSERT(m_Function) VALUES(@m_Function)
OUTPUT inserted.m_FunctionID, inserted.m_GroupID
INTO @Results;                                            -- Having a trigger requires 'INTO'
SELECT * FROM @Results                                    -- Having a trigger requires 'INTO'

然而，有一个错误：当一行被INSERTED时，OUTPUT返回m_GroupID = 0

问题：

我如何始终正确m_GroupID？
是否可以通过更简单的查询来实现目标？（因为现在很难理解所有这些“语法要求”）

Answer 1

依靠UNIQUE m_Function使用TRY CATCH至INSERT然后SELECT。演示

CREATE TABLE StackFunctionID
(
    m_FunctionID int PRIMARY KEY IDENTITY,
    m_GroupID int DEFAULT 0 NOT NULL,
    m_Function varchar(256) UNIQUE NOT NULL,
);
INSERT StackFunctionID(m_Function)
VALUES ('a'), ('b');
SELECT * FROM StackFunctionID;

DECLARE @m_Function varchar(256) = 'a'; 
BEGIN TRY
  INSERT StackFunctionID(m_Function)
  VALUES ( @m_Function);
END TRY
BEGIN CATCH
  PRINT 'Already exists';
END CATCH

SELECT m_FunctionID, m_GroupID 
FROM StackFunctionID
WHERE m_Function = @m_Function;

原子INSERT + SELECT或SELECT行（基于UNIQUE列）

1 个答案: